Experts Suggest Replacing Definition of Kilogram

fenimor writes "The kilogram is the only one of the seven basic units of the international measurement system defined by a physical artifact rather than a natural phenomenon. International team of scientists suggest replacing the kilogram artifact -- a cylinder of platinum-iridium alloy about the size of a plum --with a definition based on one of two unchanging natural phenomena, either a quantity of light or the mass of a fixed number of atoms. They propose to adopt either one of two definitions for the kilogram by selecting a specific value for either the Planck constant or the Avogadro number."

Comments

I suggest

[Anonymous Coward]

They set it to 1000 grams.

Re:I suggest

[tibike77]

Not only that, but it is also the only "basic measuring unit" that's not even a measuring unit, but a multiple of another one that's not considered "basic". At least in name. Kilo-gram. Get it ?

Actually, if they happend to re-define it based on Avogadro's number, they might as well just say the GRAM is the new "basic unit" and the kilogram is just 10^3 grams.
Why ?
Because Avogadro's number is JUST an artifact of the definition of the (kilo)gram, not a fundamental constant - it's (been originally) defined as the number of atoms in 12 grams (or, whatever, 0.012 kilogram) of Carbon-12.
Talk about circular references then...

Now, basing the definition of the kilogram (might I suggest they also change that basic to gram instead of kilogram... please) on Planck's constant somehow would be a MUCH better ideea. However, the value of that constant [i.e. 6.6260693111111 * 10^-34 and so on] makes it pretty wierd to work with unless you multiply it with 9 [to get exactly 5.96346238 * 10^-33 which makes more sense somehow]. And even then it won't satisfy some people, as I'll bet you'll hear that 0.111111 and so on *9 does not equal 1 :p
Not only that, but Planck's costant was ALSO measured "accurately" using the kilogram unit as reference.

Ok, this actually does give me a headache.

Re:I suggest

[Anonymous Coward]

BTW Physorg is stealing and Zonk is in bed with them.

Here is the original article: http://www.nist.gov/public_affairs/newsfromnist_re def_kilogram.htm

Re:I suggest

[PoopJuggler]

They set it equal to 1 pound

Re:I suggest

[FJ]

I suggest they change it to 1 pound.

Think how easy it would make converting between metric & the archaic units of measure we use in the US. It would probably be much easier than getting the US to change to the metric system.

Re:I suggest

[bcrowell]

Not only that, but it is also the only "basic measuring unit" that's not even a measuring unit, but a multiple of another one that's not considered "basic". At least in name. Kilo-gram. Get it ?
There are two common systems of units, mks (meter-kilogam-second) and cgs (centimeter-gram-second). The mks system is now more often referred to as the SI. In the cgs system, the gram is a base unit. In any case, what you're referring to is utterly trivial and/or irrelevant when it comes to the real work of defining the units. Any definition of the gram suffices to define the kilogram, and vice-versa.

Because Avogadro's number is JUST an artifact of the definition of the (kilo)gram, not a fundamental constant - it's (been originally) defined as the number of atoms in 12 grams (or, whatever, 0.012 kilogram) of Carbon-12.
It's happened before that they've changed things around so that something different was considered to be the more fundamental quantity: the speed of light used to be a measured quantity, but now it has a defined value. The whole issue is that as techniques change, you want to base your system of units on the things that can be most accurately measured (and reproduced) with the latest techniques.

Now, basing the definition of the kilogram (might I suggest they also change that basic to gram instead of kilogram... please) on Planck's constant somehow would be a MUCH better ideea. However, the value of that constant [i.e. 6.6260693111111 * 10^-34 and so on] makes it pretty wierd to work with unless you multiply it with 9 [to get exactly 5.96346238 * 10^-33 which makes more sense somehow].
I'm not sure where the <joke> tags belong here. Anyhow, giving h a defined value would be very much like the step they took when they gave c a defined value -- they did it because when techniques changed to the point where c was one of the most accurately measurable things in nature.

Re:I suggest

[Anonymous Coward]

There are two common systems of units, mks (meter-kilogam-second) and cgs (centimeter-gram-second). The mks system is now more often referred to as the SI. In the cgs system, the gram is a base unit. In any case, what you're referring to is utterly trivial and/or irrelevant when it comes to the real work of defining the units. Any definition of the gram suffices to define the kilogram, and vice-versa.

Is there some reason there isn't a meter-gram-second system? I think that would make a little more sense. No using any multipliers/dividers in the names of what are supposed to be the base units.

Re:I suggest

[Rakshasa Taisab]

If you RTFA, you'd notice they were suggesting they'd use the *number* of atoms of a certain type as the definition of KG. The Avogadro constant is currently defined based on the gram, but they are not suggesting that the constant is used, only the technique.

Re:I suggest

[aeve]

To me it seems most logical to base a measurement of mass on amount. Using the earth's gravity for the calculation is short sited and location dependent.

To define the gram as 1/12 of Avogadro's number of Carbon twelve atoms and then fix the value of Avogadro's number is my favorite solution. We can use the closest approximation we have now and then just extend the zeros to convert what was a measured value to a defined value. Something like 50184516583333333333333 atoms of C12 == 1gram.

It might seem a little crazy at first, but it's not without precedent. Something very similar was done when the speed of light was fixed for the newest meter definition. I'm sure practically it's going to be a pain but give me a pair of tweezers, some carbon and a million similarly equipped monkeys and I'll start counting.

Re:I suggest

[brianosaurus]

Makes sense. With a redefined kilogram, Avogadro is really out of a job, since his number will become useless.

Do you think the new constant will retain the name, or will it be "The New Scientist Constant Relating Atoms to Grams brought to you by BASF, the Chemical Company"?

Re:I suggest

[Biogenesis]

Hmm, it sounded big when I ordered it.

Re:I suggest

[logicnazi]

You didn't read the article or know what you are talking about do you?

Right now Avogadro's number is an experimentally determined quantity. It is defined as the number of a certain kind of atoms (carbon 12 perhaps?) needed to make some specific amount of weight. So long as Avogadro's number is so defined it doesn't make sense to define mass on this number.

However, had you read the article you would realize one of the options they are suggesting is to redefine Avagadro's number as a particular amount which will implicitly of course define mass .

Of course since mass is equivalent to energy which is defined through c which is also a fixed constant we can define mass just as easily as fixing the value of a J/s constant.

Re:I suggest

[Jeremiah Cornelius]

Dump it, based on the mass of an Avocado.

Heh heh heh... He said "Dump".

Yeah! The mass of Avogadro's dumps!

Re:I suggest

[cyberfunk2]

Avagadro's # sounds fine to me, as long as they define Avagadro's number independantly.

Like someone else noted, Avagadro's # is based on the # of atoms in 12 grams of C-12.

I suppose they could use some ultra-pure refining method to get a small amount of absolutely pure C12 (perhaps some sort of gas-centrifuge method) to get rid of the C-14 ?), or they could pick an element with only one known stable isotope. (I think there are a couple like this, gold maby?)

Then they get that element in the ultra-refined state via whatever method. Then I suppose they could create a small flat square of this material, measure the atoms 1 by 1 w/ SEM (scanning electron microscopy) and then note the length of this square (which isnt dependant on weight). There's your new unit of mass. Scale it up by whatever mulitplication factor to make it almost exactly what a current Kg is and people wont be too annoyed either (w/ having to change balances everwhere).

This way the obsessive compulsive analytical chemists and the obsessive compulsive standards people can both be happy.

As for me, I'm an organic chemist, and as long as I've got 3 places (or maby 4 in certain situations) past the decimal point, I'm happy.

Re:I suggest

[seminumerical]

There are two common systems of units, mks ... and cgs ... . The mks system is now more often referred to as the SI. ... In any case, what you're referring to is utterly trivial and/or irrelevant ...

To a scientist or engineer it is trivial, however to a (European) cop, or to someone buying butter it is not so trivial. Reporting the perp's weight in grams would not be sound practice. For everyday use the base unit needs to be visualisable/imaginable on a human scale.

Half a kilo of butter, or a pound of butter is a reasonable purchase. Grams just don't cut it. What am I getting if I ask for 80 grams of salami? Well I guess I can visualize it and some Europeans buy it that way, but the average everyday user of a measuring system is nearly innumerate. They want to buy one or two or maybe a half of something.

One of the nice things about the British system of measurement (which pretty nearly only the Americans use officially, though with a few changes) is that the units are exactly the sort of thing you often want about one of. A pint of beer, a gallon of kerosene, a bale of hay, a pint of milk if you live alone or a quart or a gallon depending on the size of your family, half an acre of land, etc. (yes, yes, I don't think a bale is an Imperial measurement).

The metric equivalents never seem to be just right, but we'll just have to live with them

Re:I suggest

[TWX]

Isn't making the unit of mass based on a particular physical thing what they're trying to avoid?

Mind you I can't come up with a better solution either...

Re:I suggest

[Anonymous Coward]

you're thinking around 3 corners

why not just take one c-12 atom and multiply?

Re:I suggest

[hawk]

Either way, as long as we do it quickly, before it's too late.

After all, an ounce of prevention is worth a pound of cure.

hawk

Re:I suggest

[Anonymous Coward]

And our feet are just the right size too.

-- A citizen of the United States of America.

Re:I suggest

[cyberfunk2]

Might be a little hard to isolate and weigh just one.

Re:I suggest

[Esion Modnar]

Better yet, make it 1024 grams. Make it consistent with the kilobyte.

Re:I suggest

[bcrowell]

To a scientist or engineer it is trivial, however to a (European) cop, or to someone buying butter it is not so trivial.
The topic of the article is only relevant to scientists -- to a very, very small set of scientists who do certain types of high-precision work. The redefinition of the kilogram they're talking about would be utterly inconsequential to everybody else.

Re:I suggest

[themuffinking]

Half a kilo of butter, or a pound of butter is a reasonable purchase. Grams just don't cut it.

You can still use kilos... using grams as the base unit does not completely eliminate kilos from the face of the earth.

What am I getting if I ask for 80 grams of salami? Well I guess I can visualize it and some Europeans buy it that way, but the average everyday user of a measuring system is nearly innumerate. They want to buy one or two or maybe a half of something.

Uh... if you need to buy eighty grams, then you'd have to say something like 2/25ths of a kilo. It's actually easier to use grams in that example. Also, if you ever need eighty grams of salami, you could just ask for one medium-thickness slice. Thus, we should use the slice of salami as a SI unit rather than the gram or the kilo. Wait, that wouldn't work...

'The moon wieghs the same as thirty-two billion slices of salami...'

Well, whatever. I say we just use them interchangeably.

Re:I suggest

[ikkonoishi]

A pound is a measurement of weight not mass.

The mass of a pound at sea level != the mass of a pound on a mountain.

Re:I suggest

[Smidge204]

So how many slices of salami are equivalent to one Elephant?

=Smidge=

Re:I suggest

[Zooka]

To a scientist or engineer it is trivial, however to a (European) cop, or to someone buying butter it is not so trivial.

Changing the base unit from kilogram to gram wouldn't render the term "kilogram" obsolete, nor mean that we would have to stop using the expression in everyday life. An 80,000 gram perp would still weigh 80 kilograms, and 500 grams of butter would still be "half a kilo".

Re:I suggest

[lgw]

The furlong-firkin-fortnight system is the one true system. All other systems are silly.

Any fool can see what faction of an acre is a rectangle bounded by a furlong and a chain, or measure speed intuitively in millifurlongs per microfortnigt. This metric system is just unintuitive.

I know just how many furlngs per firkin my car gets, what the heck is that in litres per meter?

Re:I suggest

[lgw]

Pound is used as a measurement of mass as well. Technically, one should measure mass in slugs, but there is a standard for a pound of mass.

Re:I suggest

[sholden]

To a scientist or engineer it is trivial, however to a (European) cop, or to someone buying butter it is not so trivial. Reporting the perp's weight in grams would not be sound practice. For everyday use the base unit needs to be visualisable/imaginable on a human scale.

Half a kilo of butter, or a pound of butter is a reasonable purchase. Grams just don't cut it. What am I getting if I ask for 80 grams of salami? Well I guess I can visualize it and some Europeans buy it that way, but the average everyday user of a measuring system is nearly innumerate. They want to buy one or two or maybe a half of something.


Do you think European cops say "I'm in pursuit, west bound on Main, at 33m/s"? Or do you think they might stuff using base units and say 120km/h?

Do you really say things like "It's a 100000m drive" and "I'll meet you there in 2700 seconds"?

Re:I suggest

[Anonymous Coward]

There is a far more fundamental difference between MKS and CGS units than just a simple scaling. It is that the units of electrical charge are actually quite different in both systems. Maxwell's equations in MKS units contain expermental constants; the so-called permittivity and permeability of free space. In CGS units Maxwell's equations only constant is c, the velocity of light.

Re:I suggest

[NoData]

Yeah, the kg is the basic unit in the m-kg-s SI system. It's silly, but it's true. Waaaay back in college, I remember my intro physics prof giving us this tip: Don't think of kg as a kilogram, think of it as its own unit--the "kug" he called. This way you're not tempted to think of the base units as their metric roots. (Please don't flame me with pedantic points about kilokugs and millikugs being wrong, everything ends up getting written in scientific notation anyway in intro physics, but the units needed to be SI)

Also, as for as the tautology of using Avogadro's number to define the "kug," given that Avogadro's number was itself derived on the basis of the kug...who cares? It's all arbitrary. The mass we've come to know and love as the kg has its own history, but is fundamentally an arbitrary mass. We're just trying to find a natural phenomenon to base this predetermined arbitrary quantity. Avogadro kind of already did the work for us.

What I didn't understand from the article is that the authors claim that the experimental work to establish with necessary precision this arbitrary quantity is not finished, but we should go ahead and convert the standard anyway now. Why? What's the rush? The platinum-iridium bar heading for the smelter sometime soon? Does anyone actually mass this thing for practical purposes ever? Scales and whatnots already have a standard mass programmed that's probably much less precise (but plenty precise enough) than the standard. This is all pro forma. What's the rush?

Re:I suggest

[jericho4.0]

For me, 33m/s is much easier to visualize than 118.8 km/h.

Re:I suggest

[lpenz]

Keep in mind that what is changed is the definition, and not really the actual "value". I mean, 1 kg is going to mean the same amount of mass (at least enought for most purposes). The difference is that 1kg will be based on a known measurable physical CONSTANT, and not in a comparison to some object.

Re:I suggest

[angel'o'sphere]

One of the nice things about the British system of measurement (which pretty nearly only the Americans use officially, though with a few changes) is that the units are exactly the sort of thing you often want about one of. A pint of beer, a gallon of kerosene, a bale of hay, a pint of milk if you live alone or a quart or a gallon depending on the size of your family, half an acre of land, etc. (yes, yes, I don't think a bale is an Imperial measurement).

The metric equivalents never seem to be just right, but we'll just have to live with them


But thats true for the metric system as well :D You only dont learn the "special" units in school I asume.

In german we have "pound" as well, which is just slightly bigger than yours. And ppl in shops still buy "half a pound" of meat or something.

Same for land, we have an "ar" and a "hectar" which is obviously 100 ar, and we have a "morgen" wich is 25 ar and the typical size of a field in older times.

A ar is similar big as an acre (IIRC).

Same for drinks, who cares about your pint? Do you really think we order 350ml Beer?

We order a glass of beer, obviously. And depending on beer brand it is served in a typical size.

The sizes are: 0.2l for Kölsch and Alt. 0.3l for some kins of "Pils" which consider themslelf noble. 0.4 for a standard everywhere pils,a nd your pint is just between 0.3 and 0.4. The enxt size is 0.5l for Weiten.

The same applies for nearly any metric size, no one is buying xyz litres or something except he buys 40l gasoline for his car.

Bottom line we have as many "human" metrics as you but sine the metric system is in use they got rounded to the next best number.

angel'o'sphere

Re:I suggest

[Random832]

why is it then pro-metric americans i talk to deny that anyone in metric countries use anything but kilograms when i try to cite these?

Re:I suggest

[Alexei]

A "pound" in metric countries is the same as a half-kilo. For the convenience of traditionalists, mainly.

Re:I suggest

[Anonymous Coward]

Yeah, a pound is a slug at exactly 1g. Therefore it's a force.

Re:I suggest

[trime]

0.1111 (ad infinitum) * 9 does in fact equal 1. Simply, it's the decimal representation of 1/9. What is (1/9) * 9 if it isn't 1?

Engineers. :-)

Re:I suggest

[lgw]

Actually, a slug is ~32 pounds (whatever accelelration is in ft/s^2). It's because the measurment is awkward (unlinke most imperial measures) that there is a "pound of mass" unit.

Re:I suggest

[seminumerical]

I was proposing one idea of why the kilo makes more sense than the gram as a base unit. The derived units are still needed.

I might suggest another reason why the kilo and not the gram came to be the basic unit. The standard kilo is less variable as a standard than a gram. If a piece of dust lands on the standard kilo it will have proportionately less effect on its weight than if it lands on a gram.

This provokes another idle thought. Why use such a remarkably dense substance as the standard? Perhaps because it has a much smaller surface area than, say, a kilo of aluminum. So there is much less chance of a bit of dust landing on it, or a few thousand atoms being brushed of it.

Anyway, IANAP (physicist).

Re:I suggest

[seminumerical]

I live in a part of the world where meat and cheese is often priced per 100/grams (but nobody says decagram here).

80 grams of salami would make a few sandwiches, as long as you put some tomato, pickle, and some really hot mustard on it.

Re:I suggest

[hobbesmaster]

Uhm, all the other SI units are defined off physical things. A second is defined as so many oscillations of a cesium atom, a meter is defined as 1/299792458 light*second, a kelvin is 1/273 the triple point of water and an ampere is 6.25*10^25 electrons/second passing a given point on a circuit. All of these things are based off a particular physical "thing" - it'd be impossible to create a definition that wasn't!

Re:I suggest

[stanjef1]

Other way around. ~32 slugs is a pound (mass)

Re:I suggest

[lxw56]

Let's replace the platinum-iridium cylinder the size of a plum with a carbon cylinder the size of several plums!
Brilliant!

Re:I suggest

[lgw]

Google knows all!

1 slug = 32.1740486 pounds

See, this is why the furlong/firkin/fortnight system is the best!

1 firkin = 72 pounds (of water)

As everyone knows, of course, since a pint's a pound the world `round. :)

Re:I suggest

[Synbiosis]

I wonder what moron set that to Insightful.

Re:I suggest

[Velox_SwiftFox]

Why not attoparsecs per daytenth?

Re:I suggest

[Silentnite]

So that means, it will no longer be based on Avogadro's constant, But instead be dubbed "The weight of measurement formerly known as Avogadro's base?"

*Sigh*, Its only 1am and already I've made a prince joke. Its time for rehab.

Re:I suggest

[1u3hr]

Half a kilo of butter, or a pound of butter is a reasonable purchase. Grams just don't cut it. What am I getting if I ask for 80 grams of salami? Well I guess I can visualize it and some Europeans buy it that way, but the average everyday user of a measuring system is nearly innumerate. They want to buy one or two or maybe a half of something.

The whole reason we (countries that use rational measurement systems)have standard prefixes is that we can use appropriate units and avoud huge integers or fractions in common usage. I don't know why you think this is difficult. Would you prefer to be using pounds, shillings and pennies instead of dollars and cents -- that was one reform the US did before most other countries. So do you say "80 cents" or "eight-tenths of a dollar" (or 16 shillings)? And unless you're buying in bulk, most food is bought in quantites (or units) less than a pound, let alone a kilo. That's why you use ounces, by the way. Three ounces is about 80 gm. At the deli, most food here is labelled as price/100gm (cheese, ham, etc); a the butcher and green grocer it's mostly by the kilo. It makes things a lot simpler to just multiply weight in kilos by price in dollars/kilo.

The metric equivalents never seem to be just right, but we'll just have to live with them

After a few months you adjust. Australia went metric when I was at primary school.

Re:I suggest

[tehcrazybob]

I think Avogadro's number is based on hydrogen, actually. Because hydrogen has an atomic mass of ~1, and 6.02x10^23 atoms of any type is the atomic mass in grams (carbon's mass is 12, so a mole of carbon is 12 grams) It's logical, therefore, that the system is based on the atom corresponding to 1, and the others were defined using the number derived from hydrogen.

Re:I suggest

[shawn(at)fsu]

I was thinking 2.20462262 pounds

Re:I suggest

[xsupergr0verx]

And how many of those are equal to one Rhode Island or Library of Congress?

Re:I suggest

[FuzzyBad-Mofo]

All I know is, my car gets 10 rods to the hogshead, and that's the way I likes it!

Re:I suggest

[darqchild]

Changing the scale of measurement by a couple of orders of magnitude does not affect the number of constants in an equasion.

This is to say that an object that is 1kg will not magically behave differently if we call it a 1000g object.

Re:I suggest

[Anonymous Coward]

The metric equivalents never seem to be just right, but we'll just have to live with them Yeah - I was thinking that the 2-liter bottle of soda I bought at the grocery store was exactly the wrong size.

Re:I suggest

[Madcapjack]

After all, an ounce of prevention is worth a pound of cure.

I'm sorry, I don't understand. Could you rephrase that in terms of Avagrado's number, please?

Re:I suggest

[Bush Pig]

They could just define it in terms of the number of molecules in a litre of water (or would that be a bit circular?). Of course, you'd have to be pretty careful about excluding heavy water molecules ...

Re:I suggest

[Bush Pig]

Speak for youself, pal. I reckon a litre of beer is the perfect amount. However, I concede that it _may_ go flat before you quite finish it.

And the same goes for a kilo of steak.

Re:I suggest

[novakyu]

Maxwell's equations in MKS units contain expermental constants; the so-called permittivity and permeability of free space.

Eh, permeability of free space isn't an experimental constant anymore---it's been defined to be 4*pi*some power of 10... (don't want to get up and look up), by fudging with the definition of ampere. So, SI units also contain only one measured constant, namely, permittivity of free space.

But, you are right---as far as electromagnetism goes, SI and cgs units are entirely different---even equations look different, and units don't work out unless you use the correct version! I should know---'learned it the hard was the first time.

Re:I suggest

[Bush Pig]

You'd have to decide whether your base salami was pepperoni, or csabai, or ...

Re:I suggest

[novakyu]

Anyhow, giving h a defined value would be very much like the step they took when they gave c a defined value -- they did it because when techniques changed to the point where c was one of the most accurately measurable things in nature.

And that would draw a nice parallel as well. As one of my professors once said, "You can't do relativity without c, and you can't do quantum mechanics without h."

And, now, they will both be defined constants!

Re:I suggest

[Bush Pig]

I'm a few years older than you. I still remember the horror of learning long division of pounds, shillings, pence, and of pounds, ounces (stones, hundredweights, tons, chains, furlongs, yards ... aaaargh!).

The best things we ever did in Australia (well, OK, I'm exaggerating a bit) were swing over to decimal currency and the metric system. (Actually, the _really_ best thing we did in Australia was work out how to keep the beer cold, but that other stuff is still pretty high on the list.)

Re:I suggest

[seminumerical]

that's half a gallon.

Re:I suggest

[Bush Pig]

I think we called them "poundals" when I was a lad. (No, really, I'm not kidding.) Slugs is an engineering thing, isn't it?

Re:I suggest

[utexaspunk]

i think what you're saying (and i agree with you on this) is, for example, why don't we call what we now call a kilogram a gram and what we now call a gram a milligram so that the defined value is the "default", un-modified value. maybe saying it that way will clarifiy it for those who don't understand it.

i think it would be cool if it were defined in terms of a certain number non-isotopic hydrogen atoms. i suck at math and chem though :) anyone know what that number would be?

Re:I suggest

[tibike77]

It pretty much depends on what you understand under "infinite" ;)
Given the fact that you are in bound by the laws of physics which state that on a certain (very low) level you have a certain uncertainty (sic) when you reach into "quantum level", one could argue that, in fact, 0.1111111...1111[something] for as many times you can until you hit that treshold times 9 does indeed NOT equal 1.

Re:I suggest

[Anonymous Coward]

The weight of an atom of Hydrogen-1 is roughly 1/12th the weight Carbon-12. So the number would be about 12 times the current Avogadro's number.

Re:I suggest

[1u3hr]

I'm a few years older than you. I still remember the horror of learning long division of pounds, shillings, pence, and of pounds, ounces (stones, hundredweights, tons, chains, furlongs, yards ... aaaargh!).

Mabe not. I had a few years of Imperial units too. 63360 inches to the mile, 114 pounds to the hundredweight, 21 shillings to the guinea...

Re:I suggest

[RALE007]

A kilogram of non-isotopic hydrogen would be the atomic mass of the substance (1), times the entire mass of the sample in grams (1000), times Avogadro's number (6.02 * 10^23), which would equal 6.02 * 10^26 atoms.

Re:I suggest

[RALE007]

Nope, atomic mass is based off of carbon-12, not hydrogen. Apparently it was a comprise between physicists and chemists. But you're right, for all casual intents and purposes hydrogen has an atomic mass of 1.

Re:I suggest

[Coeurderoy]

Actually, Bavaria is really sensibly Metric. A standard glass of beer is one "Mas" which is of course one litter, except during Oktober Fest (which happens mostly in september as the name, ho foggetit...) so during Oktoberfest the Mas is anything between 1/2 litter and 0.8 litter depending on the tallent of the operator and the general level of inhebriation. Servus :-)

Re:I suggest

[kamapuaa]

We order a glass of beer, obviously. And depending on beer brand it is served in a typical size. The sizes are: 0.2l for Kölsch and Alt. noble.

You buy beer by the .2L??? Germany is a nation of girly-men!

Re:I suggest

[vidarlo]

Avagadro's # sounds fine to me, as long as they define Avagadro's number independantly.

Why? The meter started as a platinium bar, and later we redefined it to something else, that matched this platinium bar. Why can't we do the same with kg? We're only trying to base it on something natural phenomen, not to redefine it. The point is that if it is a common criteria, and nnot a single object, anyone can measure a kg _exactly_

Re:I suggest

[rnash]

I live in a part of the world where meat and cheese is often priced per 100/grams (but nobody says decagram here).

If you meant per hundred grams, you should have used the hectogram (1 hg = 100g) instead of the decagram. (1 dag = 10g)

Re:I suggest

[Zentric]

it makes me thinking of what the practical use for this object actuly is? is it realy that practical to work with any way?.

Re:I suggest

[Anonymous Coward]

Only in cologne. In bavaria its per liter (mass) everywhere else it's per 0.5l.

Re:I suggest

[Anonymous Coward]

What you miss is that they *are* using SI units. A hectar is 100mx100m = 0.01km^2 and so on.

In my neck of the woods, we're metric *exclusively*:
You buy salami in decagramm - works great.
Gasoline in liters - works great.
Potatoes in kilogramm - works great.
Milk in liters - again fantastic.
Beer in big (=0.5l) or small (=0.33l) glasses - perfect.

I can't remember buying anything that was not metric and honestly the english system seems just wrong - the numbers never fit. A pint of milk? WTF?

Re:I suggest

[PedanticSpellingTrol]

I was always taught that a kilogram was the mass of one liter of water, is this merely a coincidence?

Re:I suggest

[Smidge204]

That's like asking how many pounds in a foot... Rhode Islands are units of size and Libraries of Congress are units of data. Elephants are units of mass...

=Smidge=

Re:I suggest

[Nick Harkin]

Not a coincidence, from wikipedia:

"In 1901, at the 3rd CGPM conference, the litre was redefined as the space occupied by 1 kg of pure water at the temperature of its maximum density (3.98 C) under a pressure of 1 atm. This made the litre equal to about 1.000 028 dm (earlier reference works usually put it at 1.000 027 dm)."

So the litre is defined by the kilogram.

Re:I suggest

[m50d]

In any case, what you're referring to is utterly trivial and/or irrelevant when it comes to the real work of defining the units. Any definition of the gram suffices to define the kilogram, and vice-versa.

It does cause real problems though. I've got more than one physics question wrong because I assumed a mass of 6 miligrams meant I could put 6x10^-3 into my equations. To avoid confusion the new base unit should have a different name, let's say (since I can't think of any scientists right now) the Taco. It would be approximately equal to a kilogram, with current grams becoming militacos and the metric Tonne being a kilotaco.

Re:I suggest

[m50d]

Your pint of beer is rarely close to a full pint, it's just sold that way. A litre of milk is right for a couple. A kilo of sugar or flour is exactly the right size, and about all that gets sold. Seconds are the same in either. A metre is far closer to human-sized than a foot, and about the right height for some pieces of furniture. 100m is the length of my road. I know when I've cycled a kilometre. I think you're just seeing your units as more human because you're used to them. If you used the SI units, you'd find a lot of things matched up to them.

Re:I suggest

[Bush Pig]

Yeah, I forgot about guineas.

Weird thing about the maps the army used to make at 1 inch to 1 mile scale. This sounds pretty sensible until you look at the representative fraction (1:63360). OTOH, they were very usable maps. Using a scale of 2cm to 1 km (1:50000) seems much more sensible, and just as usable.

Still, if you were in primary school when we changed to metric you certainly are much younger than I am. I was married with a child by then (just). Still got the kid. We changed to metric money when I was at high school (14 Feb 66). Did you know, some people wanted to call the dollar a Royal?

Re:I suggest

[Random832]

then why is this fact denied by every pro-metric *american* i ever talk to?

Re:I suggest

[Random832]

What you miss is that they *are* using SI units. A hectar is 100mx100m = 0.01km^2 and so on.

100m is not an "SI unit." neither is a centisquarekilometer. they are at least arguably metric though

How are you going to argue that a 500g pound or a 30cm foot are, though? and even if they are, what's the point then of denying them while claiming how great the metric system is?

I can't remember buying anything that was not metric and honestly the english system seems just wrong - the numbers never fit. A pint of milk? WTF?

If a pint isn't enough for you than buy a goddamn quart! at 946ml it should be just about a perfect fit for your liter-buying excessiveness, and it's much more readily available than by the pint.

but, seriously, the only context i've ever heard of milk by the pint is back in the days when it was delivered fresh every day. most americans buy by the quart, half-gallon, or gallon. [well, that and single-serving containers of one american pint]

Re:I suggest

[Anonymous Coward]

HA! That 0.2l easily serves as much booze as an usian pitcher filled with that sissy lemonande you call beer.

</kidding>

Re:I suggest

[squaretorus]

0.2l with an alcohol rating of 8-10% most likely.

These different sizes are there to roughly equate one glass to two units of alcohol. IN the UK we all drink ALL beers by the pint - so some pints hold 5 or 6 units of alcohol.

By reference a standard bottle of Budweiser holds about 1 unit in 250ml if I recall correctly. But then I never drink it - I like to tase my beer!

Re:I suggest

[Anonymous Coward]

Do you think European cops say "I'm in pursuit, west bound on Main, at 33m/s"?

No. European towns and cities don't have Main Streets.

Re:I suggest

[hankwang]

So, SI units also contain only one measured constant, namely, permittivity of free space.

Actually, that one is defined in terms of the speed of light, which isn't considered a measured constant nowadays.

Re:I suggest

[Anonymous Coward]

It seems you are getting ripped off.

Re:I suggest

[Anonymous Coward]

who would order 350ml of beer? the only place you get that in the uk is in bottles. a pint is 570ml thank you very much. not only do the US have near water as their beer, they don't even have proper pints!

Re:I suggest

[mickyflynn]

I had no idea bear came in anything other THAN a pint, except for the 12oz bottles. and whatever the hell it was at the haufrbau (spelling) that i drank 8 of one night when I was 17 on top of 6 shots of something which was apparently made of "fermented mountain flowers" which was not aidelwiese, but the German-Speaking Italians from the South Terolls we were sitting with could not explain further... I was hung over for 2 days.

Re:I suggest

[Anonymous Coward]

Rhode Islands are units of size...

Damn yanks! In the SI system it's football fields. ;)

(And that's real football, played with your feet, you insensitive clod!)

Re:I suggest

[1110110001]

At least in Austria we do order a quarter liter or a half liter of something. I.e. "a viertal wein" or something "aufgspritzt auf a halbe" which means 1/4 l of something mixed with 1/4 l water.

b4n

Re:I suggest

[nyekulturniy]

American, Canadian, or European?

Re:I suggest

[moonbender]

Probably they deny it because they're not aware of it; it's not a very frequent word to use, maybe a bit archaic - I think I personally never use it at all. I don't see why you would claim it, anyway, assuming you are using it as an contra-metric argument. We use pound literally as half a kilo - pound (or "Pfund") is part of the metric system, it's virtually the same concept as grams and tons, just with a different factor. And all the factors that are involved are excessively simple: 2, 100, etc - numbers that even people who are not fond of mathematics easily deal with in their everyday life.

Re:I suggest

[danila]

There is nothing in SI that prevents humans from using it. In Russia the "pollitra" (literally half-a-litre) is a very common unit of volume. So common, in fact, that, when buying vodka, people would often buy two pollitras instead of 1 litre. :) Also, units such as "nol-dva" (zero-two) and "nol-tri" (zero-three) are very usable to refer to 0.2l and 0.3l volumes respectively.

Similarly, the common size of a land plot is "shest sotok" (six hundreds), meaning, of course, 600 square metres. And most people seem to be entirely capable of saying how much meat they want using SI units. You don't need a Ph.D. to ask for "300 grams" or "700 grams" of meat.

Ditto for everything else. There is no rational reason whatsoever not to use SI units and metric system in general. All it takes is a little determination from the government to mandate its use where it matters and people will adapt very soon.

I personally don't give a shit about ignorant Americans or Brits who are/were so intent on using non-metric systems. It's their damn fault and it's their damn problem. They lose productivity, not me.

Re:I suggest

[schmink182]

The reason we shouldn't redefine the gram to be what is now the kilogram is that -- besides massive relabelling issues -- nobody wants to talk about micrograms of salt in their food. Mu is a funny symbol to draw, and it would only cause problems.

Re:I suggest

[maxwell demon]

The Bavarian Mass is written with two s (before the spelling reform, it was one ß, of course).

Re:I suggest

[maxwell demon]

Dont generalize. Only the Northern Germans are drinking beer in such small measures. In Bavaria, the 0.3l size is known as "Preußenhalbe" ("Prussian halve"), as in Bavaria, the smallest size served is usually the "Halbe" (Halbe Mass = 0.5l). Of course, a real Bavarian will drink a Mass = 1l. :-)

Re:I suggest

[Anonymous Coward]

Our pint is 0.568 litres, actually.

Re:I suggest

[BrokenHalo]

Err, according to my periodic table, the atomic mass of hydrogen is 1.00794. Sure, nearly every high-school chemistry teacher rounds it off to 1, but it won't do as a basis for the unit.

Re:I suggest

[BrokenHalo]

Same for drinks, who cares about your pint? Do you really think we order 350ml Beer?

If I were to be offered a 350 mL "pint" of beer, I would return it, as the glass would only be just over half full.

Or just under half empty, depending on how generous my disposition happened to be...

Re:I suggest

[BrokenHalo]

In any case, the numbers don't have to "fit" with the old Imperial system. Designed for an essentially pre-numerate society (or at least one that had no recourse to electronic calculators), it works very well since it is based on a duodecimal system where divisions or multiples are easily expressed in whole numbers or easily managable fractions.

Re:I suggest

[Scarblac]

The funny thing is that that fixed bound on the uncertainty is actually defined in terms of Planck's constant, the number we're talking about... so what's the fixed uncertainty of the fixed uncertainty? :-)

Re:I suggest

[Anonymous Coward]

In related news. The Kansas Board of Education has defined the kilogram as equal to 40 cubits by referring to 12:3 Leviticans for inspiration.

Re:I suggest

[JustKidding]

"I'll meet you there in 2700 seconds"

There is good reason I don't say "I'll meet you there in 2700 seconds".
When you specify a time interval in seconds, you imply a certain degree of accuracy.
2700 has 4 significant digits, whereas 45 minutes only has 2.
When you say 45 minutes, you implicitly have a larger margin for error than when you say 2700 seconds.

Re:I suggest

[TheLink]

I thought in Soviet Russia the System uses you!

And everything is measured in terms of vodka.

I suspect pollitra is probably a euphemism for The Standard Volume of Vodka and thus one litre converts to two vodkas ;).

Seriously though if it's slices of meat like ham. I just ask them for X slices of meat. And ask them to show me the first slice to make sure it's the thickness I want.

Re:I suggest

[Anonymous Coward]

Elephants are units of Elephants.

Re:I suggest

[noldrin]

You order a glass of beer who's size changes from place to place? This isn't like have a measurement system, this is like going back to the days of not having standard weights and measures.

Re:I suggest

[gillbates]

Why not 1024 grams?

Re:I suggest

[Anonymous Coward]

2.24 pounds?

Re:I suggest

[drew]

Because Avogadro's number is JUST an artifact of the definition of the (kilo)gram, not a fundamental constant - it's (been originally) defined as the number of atoms in 12 grams (or, whatever, 0.012 kilogram) of Carbon-12.
Talk about circular references then...

wouldn't be the first time it happened...

how do you think the meter came to be defined as the distance light travels in 1/299 792 458 of a second? they took the original definition of the meter, and defined it in terms of a consistent natural property.

the idea is that they want to define the unit we know as a kilogram in terms of something that never changes. 6.02*10^23 atoms of C-12 will have the same mass in 2000 years as it does now. a lump of platinum-iridium will not- as someone else points out further down, the current prototype has lost 50 micrograms in the last 100 years. it's also a measuer that could be (in theory, at least) reproduced anywhere in the world, as opposed to having your weights calibrated against the one official definition. whether that definition is based of the current definition of the kilogram, (as were the meter and the second before it) is not really relevant.

Re:I suggest

[ghjm]

Okay, then I'll meet you there in 2.7 x 10^3 seconds.

-Graham

Re:I suggest

[novakyu]

Changing the scale of measurement by a couple of orders of magnitude does not affect the number of constants in an equasion.

As far as electromagnetism goes, SI units and cgs units are worlds apart---this is mainly due to different definition of a unit charge in either system. Try searching google for Coulomb's law and cgs---if you happen upon a website that lists Coulomb's law both in SI and cgs, you will see that the equations themselves look different (well, by a constant, but that constant that is missing in cgs happen to be a "fundamental" (at least what was considered to be fundamental long ago) physical constant in SI).

Re:I suggest

[ghjm]

They are based off physical things, but not PARTICULAR physical things. If you define a second in terms of the oscillations of a cesium atom, then in principle anyone in any laboratory can create an accurate atomic clock, because in principle anyone can get ahold of a cesium atom.

The kilogram, on the other hand, is defined in terms of the ONE AND ONLY official reference kilogram. You cannot independently verify the weight of a kilogram, unless you can get your hands on the official one, which is unlikely as a practical matter. On the other hand, if the definition were changed to be 10^3 times Avogadro's number times the atomic weight of hydrogen (for example), then anyone in any laboratory could in principle create a "correct" kilogram.

The key word is "particular." Of course it's impossible to define a measurement without referring to categories of objects in the world. The goal is to avoid referring to SPECIFIC objects in the world.

-Graham

Re:I suggest

[Obfiscator]

2700 only has four significant digits if it's written as "2700." or the final zero has a bar over the top of it. Otherwise, it's two.

Re:I suggest

[hawk]

I think it's time too take me offline. Call me at 602-1023 and I'll explain it to you.

hawk

Re:I suggest

[Anonymous Coward]

Actually, pints of milk are pretty rare. At the grocery store you'll see it in quarts (~1l), half gallons (~2l) and gallons. In school cafeterias they will generally sell you a half-pint, which seemed a bit small to me by high school, but I like a lot of liquid with my meals.

Re:I suggest

[jrumney]

One of the nice things about the British system of measurement (which pretty nearly only the Americans use officially, though with a few changes) is that the units are exactly the sort of thing you often want about one of. A pint of beer, a gallon of kerosene, a bale of hay, a pint of milk if you live alone or a quart or a gallon depending on the size of your family, half an acre of land, etc. (yes, yes, I don't think a bale is an Imperial measurement).

The metric equivalents never seem to be just right, but we'll just have to live with them

A large part of your perception is based on the way SI units are used in countries that have recently changed over from imperial. Instead of selling milk or beer in 560ml multiples, countries where the metric unit is more entrenched will sell in 500ml multiples. Instead of a pound of butter, they'll buy 500g. If you've grown up buying your kerosene by the gallon, it might seem the natural unit to you, but someone who has grown up buying it by the litre will find that similarly natural.

Re:I suggest

[scribblej]

one could argue that, in fact, 0.1111111...1111[something] .111...111[something] * 9 never has eqauled 1. .111... * 9 does, though, and always has, and always will. And you got modded insightful?

They're very different numbers. I'm not even completely sure what .111...111[something] is supposed to represent. A non-terminating decimal that terminates? You need to go back to school.

Re:I suggest

[RALE007]

Your periodic table tells you the average atomic mass of naturally occuring hydrogen. Which includes all naturally occuring variations including isotopes. So er, 1.00794 is definitely not the atomic mass of non-isotopic hydrogen, 1 is a much better estimate, especially for the purposes of our calculations. To avoid trollish responses such as your own you'll also notice I didn't say 1.00000000000000, and if you're going to troll correct numbers considering the sig figs, why not also troll my use of Avogadro's number? You do realize that 6.02*10^23 isn't the most precise representation of it either right? Maybe you didn't have a handy reference telling you that though to let you troll and feel smart. Lets try to cloud the issue for the guy who says he doesn't understand chemistry and math well with irrelevant precision shall we? Now which one of us has at best mastered only high school chem? STFU troll.

Re:I suggest

[virtual_mps]

Uhm, all the other SI units are defined off physical things. A second is defined as so many oscillations of a cesium atom, a meter is defined as 1/299792458 light*second, a kelvin is 1/273 the triple point of water and an ampere is 6.25*10^25 electrons/second passing a given point on a circuit. All of these things are based off a particular physical "thing" - it'd be impossible to create a definition that wasn't!

No, none of those things is based off a particular thing. They are all based off experements that are easily repeated at any reasonably equipped lab in the world. A standard that can be used to easily verify the accuracy of a particular instrument is much more useful than one which can only be verified by checking the mass of a particular bar of iridium kept in a vault in paris.

Re:I suggest

[cannon fodder 0109]

" American, Canadian, or European?"

That's not the only problem:

Soccer pitches can be of variable sizes.

From http://www.thefa.com/TheFA/RulesAndRegulations/FIF ALawsOfTheGame/Postings/2002/05/12112.htmthe FA website

Law 1 - The Field of Play

Dimensions

The field of play must be rectangular. The length of the touch line must be greater than the length of the goal line.

Length Minimum 90 m (100 yds) Maximum 120 m (130 yds)

Width Minimum 45 m (50 yds) Maximum 90 m (100 yds)

Re:I suggest

[mp3phish]

Actually, 2700 only has 2 significant digits..

If you said 2701 then you would be correct.

Re:I suggest

[Sique]

No. No one orders Kölsch as "0.2l of Kölsch". It's rather "Bringen Sie einen Meter!" (Serve a meter!), which refers to a wooden bar of roughly three feets (1 meter) length with holes, where a glass of Kölsch is put in every hole.

Re:I suggest

[RedWizzard]

Half a kilo of butter, or a pound of butter is a reasonable purchase. Grams just don't cut it.

At least in this part of the world (Australia and New Zealand) all packaged food items which are specified by weight are specified in grams. So your half kilo of butter is in fact marked 500g. Non-packaged food items are usually specified in kilograms. I.e. fruit, vegetables, and meat usually have prices listed "per kilo". Sometimes prices are listed "per 100g", e.g. nuts, but I suspect this just to reduce the apparent cost.

Re:I suggest

[Anonymous Coward]

you're probably trolling but anyways: The dutch word for ounce means one tenth of a kilogram. When I buy salami I'll either get me one or two ounces. works just fine, doesn't require me to ask for a specific amount in grams, though that would work too. I'd guess other metric-based countries /cultures /languages have similar conventions

Re:I suggest

[Trejkaz]

I'm not sure I want litter in my beer. :-D

Re:I suggest

[seminumerical]

Same for drinks, who cares about your pint? Do you really think we order 350ml Beer?

There seems to be some misperception. For one thing I grew up with the metric system (I live in Quebec, Canada). I was remarking upon two things. Why the 1000 g Kg, originally a derived unit, became the standard in MKS (partly I say because it is an intuitively useable unit for the innumerate consumer (innumerate partially defined as people who have difficulty estimating amounts, sizes, distances, etc., or "women" as they are sometimes called), and then I mused upon naturally evolved, traditional systems of measurement. I chose as my example the former British/current American system, which is the only other system of measurement I know of. The Japanese of course, have their own traditional system of units, which I know little of, and different regions of Europe evolved conflicting standards over the centuries. Hence the imposition of the metric standard.

Anyway, not being from England, it is not my pint! And I would not only have one of them. I'd more likely have seven. And I'd probably have to drink it in 500 ml glasses not pints, since my preference is Weizenbier and I doubt it comes in pints anywhere. In Quebec we import it from Germany.

p.s., I rather like /., but I don't think I should be posting here. Although I am a computer programmer my background interest is psychology, (hence my suspicion that you will find that the basic units which evolve in any culture are "useable" amounts of something). I was amused to find this uncontroversial idea got me moderated troll! Hehe. I'll have to stick to posting about programming methodology from now on (no wait!, damn, that partially comes under cognitive psych. I had better remain silent).

p.p.s., I have never heard of anyone using the CGS system except astronomers, and that was a while ago. Does anyone know if anyone still uses it?

Re:I suggest

[lgw]

Wow, I've heard of "poundals", but never would have remembered that. I've only heard of "slugs" being used in aerospace, but it's just one more standard unit most people have never heard of, like a rod.

Re:I suggest

[Gleef]

Half a kilo of butter, or a pound of butter is a reasonable purchase. Grams just don't cut it. What am I getting if I ask for 80 grams of salami? Well I guess I can visualize it and some Europeans buy it that way, but the average everyday user of a measuring system is nearly innumerate. They want to buy one or two or maybe a half of something.

When I was visiting Italy, salami (actually most bulk food items) was ordered by the cento, which is 100g (roughly a quarter pound). If you wanted 80g, the man behind the counter would look at you funny, just like the man behind the counter in the US would look at you funny for ordering 3 ounces of salami. It's a meaningful request, but just nobody does it.

It's easy for the most innumerate person to become used to using 100g as a useful measure of food items.

Re:I suggest

[Bush Pig]

I remember rods. I think they are somehow related to a perch. I have absolutely no fucking idea what they are, though. (Give me a break, it's been nearly 50 years. Even though it was beaten into me with a stick at the time. Cold gravel, you know the story.) I suspect it's agricultural.

Re:I suggest

[Urkki]

• For me, 33m/s is much easier to visualize than 118.8 km/h.

Well, let me guess, you don't drive a car? Or if you do, it has miles per hour speedometer? Because anybody with a km/h speedometer pretty much knows how fast is 118.8km/h because they experience that speed often, even daily. But they have no direct idea how much is 33m/s.

All the confusion rises from the fact that time is not base ten. If it were, let's say there were a 1000 "seconds" in an hour, then it'd be easy, 10 meters per second would be 10 kilometers per hour ("kilosecond").

But, alas, it's not so! Our system of units is imperfect still!

Easiest way to change would be to keep the second, but scrap minutes and hours. The inconvenience would be that one day would not be any even number of kiloseconds or anything, but in everyday life that would not be a big problem since usually our days are punctuated by sleeping, which would "reset" the count anyway.

Re:I suggest

[Anonymous Coward]

Same for land, we have an "ar" and a "hectar" which is obviously 100 ar, and we have a "morgen" wich is 25 ar and the typical size of a field in older times.

A ar is similar big as an acre (IIRC).


Angelosphere, you don't know what you're talking about. How ignorant are people, if they modded your post "informative" when it's just plain wrong!

Ar = 10 m * 10 m = 100 m^2.
Hectar = 100 Ar = 100 m * 100 m.
So 100 Hectares would be one square kilometer.

It is also REALLY EASY TO CHECK WITH GOOGLE. Yes, it has a unit converter built-in in the calculator.
Type "acre" in google and it gives... guess what - about 4046 m^2. Clearly you can see that is about 4 Ar or about half a Hectar, so with a little work you would not have needed to post that drivel.

The SI system is the only modern well defined measurement system. Even the english units they use in USA are defined based on the SI units. For example, the inch is defined as 25.4 mm.

And that grams/centimeters - stuff is just obsolete. It's been decided in the seventies to get rid of the competing metric systems and adapt the SI system - where kilogram is the base weight and others are derived.

The SI base units contain such things as meter, kilogram, second. Then there are derived units like newton which is kg*m/s^2, which describes force. Also usually the SI system recognizes units with a base unit multiple of 1000, like millimeter (1/1000 m) or kilometer (1000 m). There are some other exceptions like centimeters (1/100 m) and hours (3600 s) and days (86400 s), but for example engineering drawings are done in millimeters (not centimeters). So in a blueprint, a car's length might be shown as 4200.

The very simple motivating idea behind the whole metric system is that since we use a base of ten for calculating numbers, it would be really really useful if the units were designed with that in mind too.

Re:I suggest

[TheEnglishPatient]

One of the nice things about the British system of measurement (which pretty nearly only the Americans use officially, though with a few changes) is that the units are exactly the sort of thing you often want about one of. A pint of beer, a gallon of kerosene, .......

Since when did any American want only ONE gallon of kerosene?

Re:I suggest

[famebait]

One of the nice things about the British system of measurement (which pretty nearly only the Americans use officially, though with a few changes) is that the units are exactly the sort of thing you often want about one of.

Exactly. Just like 10 is the ideal base number for counting, since we need to divide or multiply by 10 all the time.

Are you sure you're not reversing cause and effect here?

Re:I suggest

[Stephan Schulz]

Half a kilo of butter, or a pound of butter is a reasonable purchase. Grams just don't cut it. What am I getting if I ask for 80 grams of salami? Well I guess I can visualize it and some Europeans buy it that way, but the average everyday user of a measuring system is nearly innumerate. They want to buy one or two or maybe a half of something.

Actually, most people in Germany and Italy (where I have experience) buy Salami by the gramm - 100g is the most common amount for any kind of sliced sausage or meat. Some people still buy "a quarter pound" (125g) if they want a little bit more than 100g. And butter is sold in 250g pieces (only rarely referred to as "a quarter kilo").

Works fine. For cooking, I found it much harder to work with the various kinds of "spoons" in the US.

Re:I suggest

[Stephan Schulz]

Actually, the _really_ best thing we did in Australia was work out how to keep the beer cold, but that other stuff is still pretty high on the list.

No offense, but if the standard Australian beers (XXXX, VB,...) did not suck so much, there would be no need to keep it at just about freezing point. It's just to numb your palate.

Try a Camra compatible ale at one time - it's fine at room temperature.

Re:I suggest

[jericho4.0]

I'm familiar with 118 kmh, from driving a car, correct. In the general sense though, I can visualize 33 meters more easily than 118 klicks, and I can fit a second to it more easily than an hour.

Re:I suggest

[Lars T.]

A nation of people who don't have to drink their beer stale. And certainly not from the get-go.

Re:I suggest

[abb3w]

What am I getting if I ask for 80 grams of salami?

Lunch?

Re:I suggest

[Bush Pig]

I agree about the bulk of our beers, however there are some good ones here. Cooper's Sparkling Ale used to be pretty good (until they moved their brewery and turned it into a factory), Toohey's Old is OK, Chuck Hahn's Malt Shovel Brewery produces an excellent range, Little Creatures do a great Pils (although their Pale Ale sucks, imo, mostly because of an unfortunate choice of hops), and there are a few others as well (mostly small). I don't actually know anyone who drinks XXXX, VB or Foster's by choice.

In our climate, beer is better cold (although 4 degrees C is probably too cold).

Re:I suggest

[lgw]

A furlong is 40 rods, or 10 chains (a rod is 5.5 yards). Rods and chains were physical equipment used in surveying, so the units made good practical sense at one time.

A perch is a square rod: an acre is 10 square chains or 160 squre rods. Since no one does surveying using that equipment any more, the usage isn't current. I think rod and perch were synonyms originally, but perch came to imply area.

I remember the scene in Pink Floyd's "The Wall" where the students are all repeating "an acre is a rectangle bounded by a furlong and a chain" in unison, presumably because it was the most boring subject available. :)

Re:I suggest

[Bush Pig]

I remember the chain (it's the length of a cricket pitch, after all).

It sounds like you had this stuff beaten into you with a stick, too.

Re:I suggest

[tibike77]

I suppose I get moderated "insightful" because some people understand there's a difference between a non-terminating decimal number [i.e. 0.(1) which is 0.1111111... forever] and an actual terminating number that just has lots of "ones" in it.

And the difference comes from the quanta treshold used in measuring/calculating said number from some real-world phenomena, as opposed to the theoretical/mathematical representation of such a number.

Re:I suggest

[Muad'Dave]

My wife came across a reference to a guinea in a book she was reading. I looked it up, and it turns out that a guinea was 21 shillings, where a pound was 20 shillings. Supposedly guineas were a popular unit of measure in auctions where the price to the buyer was measured in guineas and the seller was paid in the same number of pounds with the auctioneer keeping the difference. Interesting.

I find the old English currency system fascinating, but at the same time bewildering.

Re:I suggest

[seminumerical]

You're right. Apart from learning them in high school I've never seen any Canadian use deca, or hecto. Decameter, hecotometer? Nope, just meter and kilometer.

BTW often Canadian newspapers use mysteriously precise estimates in the metric system. Some guy at the scene of the crime will be reported as saying that something "was 4.5 meters away". People here still use feet and miles and pounds in their mental estimates and in daily speech. Then the newspapers change 15 feet to 4.5 meters. A recent, common one was that the tsunami was about 9 meters it height. Wow! very precise estimates from people in fear and running for their lives. What they actually said was that it was about 30 feet high, which is about 9 meters.

Re:I suggest

[seminumerical]

Yah, I know. I often complain about people being too precise in their conversions, when they are just doing informal estimates.

Re:I suggest

[kamapuaa]

A nation of people who don't have to drink their beer stale. And certainly not from the get-go.

Do you speak English?

Re:I suggest

[Lars T.]

Why, do you need help understanding English?

Re:I suggest

[_Sharp'r_]

Well, since one firkin = 34.069 liters and a furlong = 201.168 meters, you'd take your furlongs/firkin number and multiply it by 0.169355961 as the conversion factor to get liters/meter.

So 30 miles/gallon = 2160 furlongs/firkin, or 365.808876 liters/meter or 12754311222.9082 meters^4 (reciprocal of moment of inertia of
area)

Hope that helps. I'm American, so am of course used to making such conversions.

Re:I suggest

[seminumerical]

We had pints of milk delivered to the door in the North of Scotland in the early 70's. That ended pretty soon after. My grandmother would sometimes skim the cream of the top of the pint.

I wonder...

[elid]

...if the change it, what would happen if they would auction off the cylinder on eBay?

Re:I wonder...

[grazzy]

Educated guess: It'd be the most expensive thing the size of a "plum" made of platinum-iridium ever sold on eBay.

Re:I wonder...

[Anonymous Cowpat]

more importantly, what would they list it's shipping weight as?

Re:I wonder...

[wmspringer]

I wonder if they'd call it "The unit formerly known as the kilogram"

Re:I wonder...

[zoloto]

I'd be sure to buy it for £ 10,000

Thank you! I'll be here all week.

Re:I wonder...

[mickyflynn]

Don't you mean GBP 2.20462262?

Re:I wonder...

[einhverfr]

more importantly, what would they list it's shipping weight as?

That's easy....

Formerly 1Kg.....

Re:I wonder...

[geekster]

More like 10K's ;)

Re:I wonder...

[Tyler Eaves]

From what I understand there isn't "A" kilogram, but really something like 80 or 100 of them at various institutions all over the world.

Re:I wonder...

[DavidTC]

It'd just be listed as '1'. Just...'1'.

Re:I wonder...

[StarManta.Mini]

2.2 pounds, of course. :)

Re:I wonder...

[iCEBaLM]

The weight formerly known as kilogram.

Re:I wonder...

[jacksonj04]

No, there is one definitive 'Kilogram' which is kept in Paris, and then copies are made and shipped worldwide to save countires having to go to Paris to check their official weights. The copies are then compared to the one true kilogram every 10 or so years (dependant upon whether it's being used for a quest to save mankind at that point).

Re:I wonder...

[rtz]

Yes, there are quite a few kilograms spread over the world. (at least one in every industrialized country), but there's only _one_ "the" kilogram. All the others are regularly recalibrated against the real thing, in Paris.

Re:I wonder...

[Talez]

Given that the kg prototype has lost 50 micrograms over the last 100 years I'm guessing 0.999995kg?

Re:I wonder...

[Loconut1389]

Weren't there 9 rings and one to rule them all?
err.. nm..

Re:I wonder...

[Anonymous Coward]

$500 per kilogram. And, they swear they aren't gouging on the shipping price!

Re:I wonder...

[Anonymous Coward]

Now there is a terrorist target if there ever was one!

Re:I wonder...

[utexaspunk]

just curious- how do they know that, exactly? what do they compare the prototype to in order to show that it has lost mass instead of whatever they're measuring it with just being off by that much?

Re:I wonder...

[Anonymous Coward]

The kilogram is a unit of mass, not weight.

Re:I wonder...

[LMCBoy]

Not to be overly pedantic (well, this is slashdot, right?), but 1.0 kg - 50 microgram = 0.99999995 kg.

Re:I wonder...

[Cska Sofia]

But since this is The Kilogram, it's still a kilogram. We just have to add 50 micrograms to every other kilogram measure in the world.

Re:I wonder...

[Cska Sofia]

"Puny humans! Guess the weight of this bag of apples to the nearest nanogram or I will destroy your world, a-ha-ha-ha!"

Re:I wonder...

[Zog The Undeniable]

At least working out the postage would be easy.

Re:I wonder...

[Net_Wakker]

Given that the kg prototype has lost 50 micrograms over the last 100 years I'm guessing 0.999995kg?

Since the kilogram is defined as the weight (or mass, I'm always confused by the two) of the platinum cylinder, it still weighs 1 kg. Everything else in the universe however has gotten heavier, 50 micrograms per kilogram to be exact.

Re:I wonder...

[maxwell demon]

And given that E=mc^2 (and c obviously didn't change in the same time), this means that the total Energy in the universe has increased. Now we have disproven Energy conservation!

Re:I wonder...

[ESqVIP]

Nah, personally I don't think it's worth more than £ 2.20462262.

Re:I wonder...

[Fallen_Knight]

mass was expended in suns and by other means to create energy...?

Re:I wonder...

[Loconut1389]

off topic? try +5 Funny

"No, there is one definitive 'Kilogram' which is kept in Paris, and then copies are made" ... "then compared to the one true kilogram"

I read that last part like "The One (true) Ring"

Seen LOTR lately?

Use your mod points for something worthwhile.

Re:I wonder...

[Kjella]

Actually, you have to multiply with the inverse (1/0.99999995) so everything is 50,0000025000001250000063 micrograms heavier per kilo. Rounded up.
</mode>

Kjella

Re:I wonder...

[Alberic]

there is one definitive 'Kilogram' which is kept in Paris

So that's why the USA didn't go metric !

Nice but...

[winterdrake]

This kind of idea pops up every so often, usually doesn't pan out since it's too hard to get everyone to change.

Re:Nice but...

[Anonymous Coward]

well they dont plan to change the use of kilogram, only the definetion of it, so everything should remain the same.

Re:Nice but...

[Anonymous Coward]

Generally when they do this sort of thing they set it up so the new value of a kilogram is identical to the old one (or close enough that no one can measure the difference with current technology), so the only things that have to be changed are the textbooks.

Re:Nice but...

[piquadratCH]

This kind of idea pops up every so often, usually doesn't pan out since it's too hard to get everyone to change.

They only want to change the definition. One kilogram will still be one kilogram, no matter how exactly it is defined.

Re:Nice but...

[northcat]

How the hell is parent Off-Topic? Is everything other than lame-ass, non-funny jokes Off-Topic?

Re:Nice but...

[DavidTC]

Well, yeah, one kilogram will always be one kilogram. They could define a kilogram as 'the weight of the sun', and 'one kilogram' would still be 'one kilogram'.

I think you mean 'things that formerly massed one kilogram would continue to do so'. (Barring any relativitistic changes in mass, of course.)

Re:Nice but...

[Gabrill]

If that was the case, then they would lose all support for the conversion. I'm guessing that some anal retentive board somewhere has fit everytime they can't accurately and repeatedly measure the mass of 1 cm^3 of water (1 gram).

Re:Nice but...

[Weird_one]

A part of the problem is that was the originally proposed definition when they went about re-defining the fundamental measurements of SI unfortunate that quantity varies with temperature and atmospheric pressure.

does this mean

[zerkon]

I'm going to finally lose some weight?

Re:does this mean

[zxnos]

that or put on... :P

Re:does this mean

[veg_all]

no.

How about ...

[canwaf]

1 litre of H2O at ATP?

Re:How about ...

[Anonymous Coward]

is that H2O from the tap, or distilled?

Re:How about ...

[csrjjsmp]

I believe you mean 1 litre of H2O at STP.

Re:How about ...

[Mistlefoot]

But isn't a litre of water 1 kilo of water at ATP?

Circular weight system?

Re:How about ...

[InfiniteWisdom]

The point is to have something that you can define just by counting some phenomenon or natural objects. For example a second is defined as:
"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."

and a metre is defines as:
The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.

Unfortunately, there hasn't been a good way to count the number of atoms with any kind of precision, so that has precluded a good definition of the kilogram so far. Maybe now the physicists can actually count atoms accurately enough.

One could define it as the mass of some number of H2O molecules, but maybe its easier a measure a quantity of light or to count some larger atoms.

Re:How about ...

[csrjjsmp]

Never mind, you clearly don't, as water only has the density 1kg/L at it's densest, 3.98 C.

Re:How about ...

[Pinkfud]

Why not just measure all the mass in the universe and divide it by some constant that gives the current Kg value? Then it would be a true universal value. Heh.

Re:How about ...

[tanguyr]

It's also the amount of water in a 10cm x 10cm x 10 cm cube.

Re:How about ...

[einhverfr]

Why not just measure all the mass in the universe and divide it by some constant that gives the current Kg value? Then it would be a true universal value. Heh.

One problem.

E=mc^2

So you would have to measure all the mass and all the energy in the universe, plug it into that equasion and move it over (maybe E+mc^2?) before you could come up with a universal answer.....

Good luck ;-)

Oh, and then pray we don't find any more (like, say, dark matter).

Re:How about ...

[Qwerty4]

1 litre = 10 cm^3 therefore no circular reference.

Re:How about ...

[Dizzle]

Now, I know those definitions are techincally correct, but who thinks these ideas are easily applicable? I mean, the point of having a definition is to be able to calibrate everything else, right? So how on earth is a watch manufacturer or repair person going to say "alright, the cesium atom vibrated 9,192,631,769... 9,192,631,770 times. That's a second."

Is there actually a method of directly using these definitions?

Re:How about ...

[InfiniteWisdom]

Nobody cares about watchmakers. Having a universal, fundamental definition is important for scientific purposes. Being repeatable, precise and fundamental is far more important than being "easy'. You and I will continue to define the second as "the time the second hand on my wrist watch jumps by one unit" and a kilogram as "the mass that causes my bathroom scale to display 1.00"

Re:How about ...

[Anonymous Coward]

Short answer: yes. That's what an atomic clock *is*.

Re:How about ...

[another_henry]

Actually, yeah - caesium reference frequencies, i.e. "atomic clocks" actually do count the vibrations of caesium atoms. It can even be done by amateurs.

That guy has clocks accurate to better than 1 part in 10^13, which means that the clock will only be wrong in its count of 9,192,631,770 vibrations/second once every thousand seconds.

Re:How about ...

[mattyrobinson69]

no, 1kg is what causes most peoples bathroom scales to display X, where :

0.6>X1.7

Re:How about ...

[stilwebm]

1 litre = 10 cm^3 therefore no circular reference.

10cm^3 of what? Under what conditions? Are 10cm^3 of water at 101.325kPa (1atm) equivalent to 10cm^3 of water at 50kPa? Because pressure affects volume of a given mass, and pressure = force / area and force= mass x acceleration, you have a circular reference still.

Re:How about ...

[matthewp]

Dizzle wrote: Now, I know those definitions are techincally correct, but who thinks these ideas are easily applicable? I mean, the point of having a definition is to be able to calibrate everything else, right? So how on earth is a watch manufacturer or repair person going to say "alright, the cesium atom vibrated 9,192,631,769... 9,192,631,770 times. That's a second."

Is there actually a method of directly using these definitions?

National standards laboratories, like the UK's NPL, use these definitions to calibrate standards for their own use and for that of commercial calibration laboratories. It's a lot of work, but it's reproducible and doesn't depend on any particular set of instruments. The watchmaker's equipment may be another couple steps removed from this process, but ultimately any instruments of any real accuracy can trace their calibration back to a reference standard somewhere.

Re:How about ...

[mattyrobinson69]

crappy slashdot stealing < signs. crappy html for using them.

0.6>X<1.7

Re:How about ...

[tawhaki]

A Litre is a volume unit... Simply 10 cm... Of course, the mass of 1 litre of water will be different depending on the temperature of the water, but yet 1 litre = 10 cm... If you change the temperature of something, its volume will change. So, there's no circular reference...

Re:How about ...

[Anonymous Coward]

> 1 litre of H2O at ATP?

That would only work for a given value of Earth's atmospheric pressure. While it's not likely to change dramatically anytime soon it's certainly not a constant, universal value. Better to find something that wouldn't tie the measurement to our current atmospheric conditions, or even to this planet.

Re:How about ...

[Mycroft_VIII]

Don't you mean:
0.6<x<1.7
?

Mycroft

Re:How about ...

[theEd]

One could define it as the mass of some number of H2O molecules, but maybe its easier a measure a quantity of light or to count some larger atoms.

That would be similar to the original definition of the gram, which is the weight of 1 milliliter (1 cubic centimeter) of water at 4'C.

Re:How about ...

[Waffle Iron]

One could define it as the mass of some number of H2O molecules, but maybe its easier a measure a quantity of light or to count some larger atoms.

It seems to me that just counting atoms runs into problems with relativity. Due to e=mc^2, the mass of some number of H20 molecules will be slightly different depending on what state they're in. By my quick calculation, the difference in energy between water and steam vs. the intrinsic energy of a gram of water is almost 1 in 1 billion. That's not much, but it's still not a rock-solid definition because it depends on external pressure and temperature factors.

Even if constant temperature and pressure were assumed, for water the precise energy is a function of wishy-washy chemistry lab details including what fraction of the molecules disassociate.

It seems if we're counting particles to determine energy/mass, it should be something as simple as possible. The photon idea seems best to me.

Re:How about ...

[Geoffreyerffoeg]

Don't you mean 1 L H2O at STP?

Adenosine triphosphate doesn't have much bearing on the mass of a quantity of water, even though it does provide biochemical energy to the physicists who're measuring it. :-)

Re:How about ...

[lgw]

That's actually very insightful! The mass of an atom isn't constant, only the mass of its matter component. It could be defined at a goven temp, but why not use light?

Of course, we've found that the speed of light depends on the environment ('vacuum' is hard to define these days), which makes the definition of the meter interesting, and the emission of cesium atoms isn't constant, AFAIK, it just averages out quite well.

Re:How about ...

[bleckywelcky]

Well, your watch manufacturer is simply producing watches for the public. To an individual person it really doesn't matter if they are ahead or behind in their day by 15 or 20 seconds ... maybe even +/- 5 or 10 minutes. So to them, a watch that can hold time to within 5 or 10 seconds over the course of a month or so is just fine. I'm not sure how accurate a quartz watch can get, maybe it's even more like 5 or 10 seconds over a year or so?

Anyways, it's one thing for a watch manufacturer to achieve a certain accuracy. It's another thing when you are trying to transfer a satellite from high earth orbit into an elliptical sun orbit to intersect neptune or a KBO. The accuracy requirements for making certain burns to change trajectory, or making a control movement of the momentum wheels is another thing. Or in a particle accelerator, when to activate certain portions of the cyclotron, etc.

These definitions are for the purposes of science and technology. A company can offer a service where they dumb down the definition for the public.

Re:How about ...

[Anonymous Coward]

In all fairness, he didn't actually build the guts of the atomic clocks. I doubt this could be done easily by any single person. Especially the getting of cesium in post 9/11.

Re:How about ...

[fbform]

Ah, that's how you interpreted it is it? I myself was wondering what the Association of Tennis Professionals had to do with the defining the kilogram.

Re:How about ...

[another_henry]

Good point - though I don't see why caesium should be restricted post 9/11, it's completely impractical as an explosive. Would cost crazy money for enough to do any damage to anything, while you can make things like acetone peroxide from off-the-shelf materials (most of the suicide bombs used by the Palestinian terrorists use acetone peroxide as the explosive).

Re:How about ...

[vrt3]

The mass of 1 litre of H20 is *not* 1 kg, despite what many people believe. It's OK to use that definition in everyday informal contexts, since it's close enough to the real value, but it's absolutely not good enough in rigorous scientific contexts.

At standard pressure, the density of water is less than 1 kg/m^3; at 4 C the density is at its maximum: 999.972 kg/m^3. In other words: at standard pressure and 4C, the mass of 1 litre of water is 0.999972 kg; at other temperatures it's less than that.

I think a kilogram in the beginning was meant to be the mass of 1 litre of water, but an error occured somewhere.

Re:How about ...

[Detritus]

The problem with water, actually one of the problems, is that it isn't a uniform substance. You can have two liters of water that have different masses. This is because of hydrogen and oxygen isotopes that are present in varying amounts depending on where you obtain the water.

Re:How about ...

[Anonymous Coward]

Are 10cm^3 of water at 101.325kPa (1atm) equivalent to 10cm^3 of water at 50kPa? Because pressure affects volume of a given mass

Holy shit, I think your brain just dereferenced a null pointer. Recompile that module with -DDEBUG and see if you can repeat the error by asking yourself: What is heavier, 1Kg of water or a 1Kg of lead?

Re:How about ...

[rgmoore]

Now, I know those definitions are techincally correct, but who thinks these ideas are easily applicable?

They're not intended to be easily applicable; they're intended to be as precise as possible. Even if it's very difficult to make the precise measurements so that it's only possible in a few labs, it's better to have the base definition be as tightly nailed down as possible. After making the hyperprecise technical definition, it's possible to make easier to use but less precise derived measurements that most people will use in practice. And, FWIW, in the case of the kilogram the new definition is almost certainly going to be easier to use than the old one, because it will actually be repeatable.

Re:How about ...

[InfiniteWisdom]

No it wouldn't because it depends on the definition of the centimeter, of temperature and would vary depending on the gravitational fields acting on it and so on. X molecules of water, however are X molecules no matter what.

Re:How about ...

[stilwebm]

I agree that the litre is a volume unit, but the grandparent post was trying to define 1 kilogram with a litre of water. Btw, 1 litre is 1000cm3.

Re:How about ...

[dtaczalski]

Don't you mean 1 L H2O at STP?

Why not 1 G of P2P with FTP ?

Re:How about ...

[Geoffreyerffoeg]

Why not 1 G of P2P with FTP ?

IIRC, FTP (TCP 21) isn't P2P. RTFM: RFC 959.

News Why?

[Anonymous Coward]

And this is news why? It obvivously makes sense to have the kilogram based on some universal constant as opposed to a block of metal sitting in some museum.

Re:News Why?

[InfiniteWisdom]

So anytime anyone does anything that "makes sense" is no longer newsworthy? For instance, if congress were to repeal the Patriot act or the DMCA that would not be newsworthy to you?

Re:News Why?

[Anonymous Coward]

Because it is information about a recent event or happening.

Just wait.

[jwcorder]

The next thing you know they will be trying to get the US to switch from imperial units to the metric system....

Re:Just wait.

[Anonymous Coward]

Oh wait..

They've already switched.. at least officially.

Re:Just wait.

[nxtr]

The only countries left that don't use metric are America and Bhutan. Bhutan is a fundamentalist islamic country that doesn't even have any phones yet. I guess we can see what the American technical level is.

Re:Just wait.

[bobscealy]

I have always found it intriguing that the US both celebrates the day of its independance from the British empire and continues to use old British units of measurement.

Re:Just wait.

[ajdavis]

!!

Bhutan is a devout BUDDHIST country, you hoser. And they have TVs now, although when I first read about that (more than 5 years ago), the Bhutanese were quite reasonably shy about appearing on it. Hence they had to cajole some poor sod to read the national news in a pained monologue. If you see some of the recent Bhutanese movies, though, it appears things are changing fast. I have no idea how they weigh their TVs and Buddhas, though.

On topic, I think it's great that they're using Avocado's Number to define the kilo. So let's see, 6.022 x 10^23 avocados would weight ~1.8 x 10^23 kilos, or 28 Earths (this measurement based on the standard platinum-iridium avocado that was shipped to me from Paris, which is significantly larger than a plum, but was free to ship, since any attempt to weigh it would cause fatal recursion).

Re:Just wait.

[KarmaMB84]

We also happen to speak English. Why bother throwing out something like a system of measures? That would just be childish.

Re:Just wait.

[Anonymous Coward]

Even the Brits have changed over to Metric now (except for distances, for some reason...)

Re:Just wait.

[Nogami_Saeko]

Unless something way better was to come along...

N.

Re:Just wait.

[spuzzzzzzz]

I think GP meant Burma, not Bhutan, which IIRC still uses imperial measure. It's also a military dictatorship although I'm not sure what their television penetration levels are.

Re:Just wait.

[TheUglyAmerican]

US Congress adopted the metric system in 1893. What more could anyone want? http://www.unc.edu/~rowlett/units/usmetric.html

Re:Just wait.

[Anonymous Coward]

The difficulty in going from imperial units to the metric system in the US has nothing to do with the educational system. You will find no engineering or science educated persons in the US who do not know how to use the metric system. It has nothing to do with national pride either (though some people try to push that agenda) since there are several laws made to try to switch to the metric system, in particular the Education Amendments of 1974, the Metric Conversion Act of 1975, the Omnibus Trade and Competitiveness Act of 1988, and the Fair Packaging and Labeling Act.

The reason that conversion to the metric system has been so slow is because the government was in turmoil in the 70's when the big push to go metric occurred in the US. Without strong support from the government, particularly in the way contracts with the US government are defined (where the specifications would be metric vice imperial units), industry was not motivated to change. For most industrial or technical companies, the short term gain of not putting down the investment for switching to metric outweighed the questionable gains of dealing with metric-only companies and metric-only government contracts. Since neither of these situations have occured, it seems that they were right, from the economic perspective. Additionally, a greater fraction of the GNP of the US was based on industry during this time period. Switching then would probably cost more than the Y2K fixes.

For those who have experience with technical documentation, it is expensive to revise documents and drawings. You must ensure that you don't make any errors and that you QA the document afterwards. If there is a contract with another entity involved, you will need to renegotiate the contract at a loss. For the most part, it is impossible to update your companies' finished products in this case. Considering that new products, especially in industrial settings, are often evolutionary changes of the current product, if you switched to metric, the new product will have technical specifications in imperial and metric. Having both is even a greater pain than having imperial units.

The only way to solve this is for a very strong government push of metric (including making all government contracts metric only) and for a metric conversion protection act where companies are not required to renegotiate contracts if they switch their documentation and technical specifications to metric.

Re:Just wait.

[Anonymous Coward]

The US also pioneered decimal coinage in 1786. Without this step, the metric system might not have been as popular throughout the world as it is now (where people from many countries marvelled at how easy a decimal currency system was and realized how that would help with other number).

Re:Just wait.

[Grishnakh]

I thought Liberia was the only other country that didn't use metric. Of course, Liberia isn't exactly a economic or technological powerhouse either...

Re:Just wait.

[Anonymous Coward]

Ah freedom. It's great because you can even keep doing things you did before you were free if you want.

Re:Just wait.

[Anonymous Coward]

We also happen to speak English.

...not very well, I'm afraid... 8^)

Re:Just wait.

[bobscealy]

Imperial measurements are kind of like that old pair of underpants. I know they are comfortable and familiar, and in some ways your closest friend, but they are also full of holes and won't survive another wash. It is time to retire them to the garage as a rag and get yourself some new ones - they might feel uncomfortable and foreign at first, but they will grow on you (not literally, of course).

Re:Just wait.

[Guppy06]

Depends how you look at it. We call the things we use "pounds" and "feet," but we abandoned the flawed British standards in the 1890's (their yard shrank, their pound leaked), instead basing them on the SI standards. A pound is defined as 0.45359237 kg and a foot is 0.3048 m.*

Also, we were the only ones sane enough to base our unit of volume/capacity on the cube of our linear standard (1 gal US = 231 in^3, as it's been since the 1800's or so). Both the British gallon and the SI liter both had ugly/cumbersome definitions involving a sample of perfect water at a given temperature, pressure and local gravitational acceleration (the French got the litre right from the first, but then they broke it, and then it was fixed again, meaning the definition of "liter" has changed by tens of microleters over the past century).

* These are actually numbers agreed upon by the foot/pound using world in 1959. Before that, in the US, the number of kilograms in a pound had more digits and a foot was 1200/3937 m.

Re:Just wait.

[Barryke]

And the article reads:

American scientists and engineers have always been among the leaders in improving, extending, and revising the metric system.

Owh dear.
Improve the metric system?
Either that is a multiword-typo, or the author is a real American.

(i mean -- thinking that ABN-Amro, ING Group, Shell or Philips are American)

.. PS, do you know who founded New York?

Re:Just wait.

[neil.pearce]

EU legislation now forces produce to be displayed in metric weights (though you may in addition display in imperial and any made-up system [jedis? groats?] you can think of). This hasn't stopped jobs-worths trying to prosecute whenever they see a lb (pound) sign though...
Interestingly, British school-children have been taught, in mathemetics/physics classes since the late 70's, virtually solely metric. Yet, (myself included) I'd wager most of 'em would have no idea whether 400g of turkey was enough for a single meaty sandwich, or enough to feed a family for 4 for a week.
We weigh ourselves in imperial stone and pounds, but cannot cope with pure US "pounds". Rest of the EU does KG. Living in a cosmopolitan house-hold, the switch on the bathroom scales goes back and forth daily, to the annoyance of everyone...

(excuse bad grammer/spelling == drunk)

Re:Just wait.

[Anonymous Coward]

I have always found it intriguing that the US both celebrates the day of its independance from the British empire and continues to use old British units of measurement.

Christ, you're easily amused. As well be intrigued by the fact that people in the US still speak English, despite celebrating the day of independence from England.

Sorry. Just feeling grouchy today.

Re:Just wait.

[Mycroft_VIII]

That actually depends on how you define 'english'. If you define it simply as the language spoken in England, them by definition anyone there speaks it rather well.
However some mean a specific form of english, and in this particular conext (how well Americans speak it) they're often refering to how closely to the english of the time when Europeans, especially British, first settled the americas in the 1500-1600's. In that case it's my understanding the honors go to a subsection of America (or at least did about a decade ago when I saw this discussed on nova or some such). There are villages and such in the appallation(sp?) mountains that have been sufficiently isolated that thier language use has drifted less than in the rest of the english speaking world.

Mycroft

Re:Just wait.

[tverbeek]

If he meant Burma, he really meant Myanmar (aka the country formerly known as Burma)

Re:Just wait.

[Anonymous Coward]

I have always found it intriguing that the US both celebrates the day of its independance from the British empire and continues to use old British units of measurement.

And it's my understanding that Great Britain doesn't use the "old" British units...

-cmh

Re:Just wait.

[Anonymous Coward]

Especially as Britain uses more metric units than the USA :).

We still have some leftovers - you'll get our pints when you pry them from our cold, dead hands - but mostly we're metric.

Re:Just wait.

[Anonymous Coward]

We also happen to speak English. Why bother throwing out something like a system of measures? That would just be childish.

Childish, eh? How about the fact that virtually the entire world uses the metric system? Outside the U.S. I think only a few small countries in the Caribbean and Asia use imperial units. And with today's shrinking village of a planet every year that the U.S. sticks to the imperial system is costing tons of money in conversions, separate sets of tools and machine parts, errors shipping and replacing the aforementioned items, etc.

And here's a very visible news story from 1999 that shows why it's a bad idea not to switch:
http://www.cnn.com/TECH/space/9909/30/mars.metric. 02/
NASA lost the $125 million Mars Climate Orbiter because of errors in coverting imperial and metric units.

Finally let me give you a simple example of how convenient the metric system is:
One liter of water at sea level and room temperature weighs 1 kilogram. One milliliter of water weighs 1 gram. 1kg of water fits in a cube 10 centimeters per side. Water boils at 100 degrees Celsius at sea level and freezes at 0 degrees. There are 10 millimeters in a centimeter and 100 centimeters in a meter. A kilometer is 1,000 meters.

Now you tell me, quickly, exactly and off the top of your head, how many inches in a foot? How many inches in a yard? How many yards in a mile? How many inches in a mile? How much does an ounce of water weigh? A pint? A quart? A gallon? What size cubes would such quantities of water fill? Not to mention that ounces are used for weight and volume measurements... At what temperature does water freeze and boil in British units? What's the speed of light in yards per second? Inches per second?

Ladies and gentlemen of the jury, the prosecution rests is case.

Re:Just wait.

[Anonymous Brave Guy]

Why bother throwing out something like a system of measures? That would just be childish.

We've been trying to tell you young upstarts the same thing ever since you forgot how to use the letter "u". :-)

Re:Just wait.

[Anonymous Coward]

Yeah, the last thing I want them doing is using metric units on the packaging of my Freedom Fries.

Re:Just wait.

[hawk]

Actually, you've hit the *real* reason we split.

We *don't* have the same units. Those slimey limeys shortchanged us. It takes, for example, six "colonial" gallons to match five "imperial" gallons.

17% off the top of *every* glass of beer.

You'd revolt, too!

hawk

Re:Just wait.

[Jeff DeMaagd]

A lot of units in the US measuring system differ from the Imperial system.

I don't know if it is true, but my understanding about the reason that the US didn't fully adopt SI is that people thought the gas stations were trying to rip them off. So not only does the US start (and finish) wars about oil, misunderstanding and confusion over it had a hand in preventing a metric changeover.

If it is any help, big industry is Metric. US furniture, automakers and any kind of industrial design is largely metric now. US cars have been mostly metric since the mid 80's. Road planning and surveying are mostly done in metric internally, and converted for public information. I've heard about one law that says no speed limit sign may be posted in metric, which is understandable, 60 MPH is about 100kph. Some jerk could just see the 100 and speed on his merry way as if it were MPH.

Re:Just wait.

[mbrewthx]

Yes but the old phrase
"give him an inch and he'll take a mile"
just doesn't cut it as
"give him a centimeter and he'll take a kilometer"

Re:Just wait.

[Fishstick]

>Liberia isn't exactly a economic or technological powerhouse either...

Nope, yet all the cruise ships seem to have Liberian registry...

I've always wondered what the deal was with that

Liberia is the oldest democracy in Africa which was founded in 1847.
In 1948, the Republic of Liberia adopted maritime and associations laws to serve the needs of world commerce.
Liberia was one of the first offshore, zero tax jurisdictions.
Its excellent safety record and low loss ratio are attributed to its mandatory safety inspection program for vessel hull, machinery, safety and communications equipment, crew training and qualifications. Liberia has been an active member in the International Maritime Organization (IMO) since 1959 and has worked to transform IMO policy into effective action.

For more than 50 years, Liberia has operated a premier ship registry with one of the largest fleets of merchant ships in the world. About 1900 ships fly Liberian Flag. Vessel types include tankers, bulk cargo, general cargo, containers, reefers, offshore drilling units, barges, passenger vessels, fishing vessels, yachts and other small crafts.

The soundness of the Liberia Maritime Program, the high quality of the vessels and the professional skills with which they are administered are internationally recognised by lending institutions and shipyards that accept mortgages on vessels as security for payment.

Re:Just wait.

[Anonymous Coward]

If you've ever looked at the back of a large ocean going ship, you may have noticed that more often than not, the ship says either "Panama" or "Monrovia" on it. (those being the capitals of the Republic of Panama and Liberia respectively). The ship will also fly the flag of it's country of registry even though the crew and owner are probably not from there. Here's a list (there are other popular countries too, but you don't see them as much).

http://www.marad.dot.gov/Marad_Statistics/MFW-01-0 3.htm

The reason is that it's legally advantageous to register your vessel in certain countries, even if it's owned elsewhere.

I can understand stable countries like Panama or the Bahamas as places of registry, but how can a country as messed up as Liberia make this happen? Is there actually a functional Liberian shipping bureaucracy? Or is it just a bunch of people in Switzerland with "Liberia" on the office door? (the Liberian pitch) Then again, if you really want to avoid taxes, perhaps an unstable registry is to your advantage...

Re:Just wait.

[Zemran]

I had always been wondering what the United States, Liberia and Myanmar had in common. I can now be the most boring fart at a party when I ask 'do you realise what the United States, Liberia and Myanmar have in common?'.

Re:Just wait.

[mark-t]

But the irony in what you just said is that the Brits use the metric system now.

Re:Just wait.

[Anonymous Coward]

Thats idiotic.
I grew in Canada when the conversion to metric was under way and never have I heard anything so....
oh wait, the US you say?

Never mind. I'm a regular on Fark so I totally believe that.

Actually its funny to still see how the old anglophones here in Canada still hold to their F system for weather instead of celsius. I asked once someone who worked at the only english tv station why this was the case. He said he didnt know since he once did a poll in the studio and asked people to tell them what freezing point is in F and one out of 15 knew.
Most of the staff was under 35 and didnt know any system but the metric.
Of course, he says many of the old listener supposedly went insane when the Queen's picture was taken off during the sign-off. Dont laugh, the hockey arena in Winnipeg when it used to have a NHL team had a H-U-G-E picture of the Queen on one end of the rink, so I guess the old farts who are nostalgic for the queen still have a lot of sway..

Between them and the hillbilly with 12 toes, I wouldnt want any to drive a car.

tt

Re:Just wait.

[ocelotbob]

How's it way better? The imperial system is broken up so that the units are resonably scaled as it is. For distance, you've got inches, feet, and miles. Small stuff, you measure it in inches, or fractions thereof. Larger things you measure in feet, and for distances, you use miles. Fluids, you use ounces for small, cups, pints and quarts for medium, and gallons for large measurements. Converting to metric would cost billions of dollars for not much real benefit.

Re:Just wait.

[FatTux]

A little OT, but curious. In the 70's, Nestle distributed powder milk in Brazil in cans with precisely net 454 grams (Brazil uses the metric system for more years than I can tell, perhaps more than a century). I was a kid then, and found to be strange that a product was shipped with such a "broken" number for its quantity.

It took years to me to realize this mass is exactly one pound.

The catch here is that this product was not imported, it was manufactured in Brazil. I can't tell when this has been changed, but today the same product is shipped in 400 grams and 1,000 grams cans.

Re:Just wait.

[uberdave]

The real kicker of the thing is that all American weights and measures are metric already. Most of them don't know it though.

Re:Just wait.

[Anonymous Coward]

Reefer madness!

Re:Just wait.

[iroll]

They're only referred to as the "British" or "Imperial" units by tradition; really the modern units used in the US diverged from their counterpart Imperial units in (or before) the 19th century and are more properly called "US Customary" units.

Re:Just wait.

[Abcd1234]

Well, here in Canada, we have all kinds of odd measurements in metric that happen to be conversions of Imperial measurements, the most obvious being pop/soda cans and bottles. This is mainly because it's cheaper to print a new label than to make a new container with a volume that's nice, round number of SI units.

Re:Just wait.

[Anonymous Coward]

Sounds like British VAT :(

Re:Just wait.

[fbform]

foot is 0.3048 m
foot was (1200/3937) m.

Minor addition - the first definition comes from the fact that an inch is defined to be 25.4 millimeters. The second definition arose from the older definition of an inch, which was (1/39.37) of a meter. This foot is now called a Survey Foot, and is still used by the USGS (and just about nobody else).

The discrepancy between the two feet is about 2 parts per million.

Re:Just wait.

[Anonymous Coward]

Bhutan is a fundamentalist islamic country

Buthan is a small, beautiful country somewhere in the Himalaya Mountains between Nothern India and Tibet. Buthan isn't an Islamic country at all. The main religion is Buddhism. Don't they teach you anything in your country?

Re:Just wait.

[Anonymous Coward]

Don't make it too difficult, just give them the answer. The Dutch of course, and those companies are all Dutch, except for Shell which is Dutch/British.

PS Guess who inspired the American declaration of independence? Correct...The Dutch. The declaration of independence is based on the document in which the Republic of the Seven United Netherlands declared their independence form Spain in 1581. Some parts were copied word for word...

Re:Just wait.

[kamapuaa]

tons of money in conversion

Is "tons of money" some kind of metric unit of wealth?

Re:Just wait.

[illuvata]

the SI liter both had ugly/cumbersome definitions involving a sample of perfect water at a given temperature, pressure and local gravitational acceleration
As far as I know, one litre is 1000 cm^3. How did you think it is defined? Perhaps you are thinking of the old definition of a kilogram?

Re:Just wait.

[Anonymous Coward]

Both the British gallon and the SI liter both had ugly/cumbersome definitions involving a sample of perfect water at a given temperature, pressure and local gravitational acceleration
Wrong, since 1964, a SI liter is:

* 0.001 cubic metres,
* 1 cubic decimetre,
* 1000 cubic centimetres
* the volume of a cube of side 10 centimetres.

I would say it makes more sense than a random 231 quantity, but that would be a troll :-)

Re:Just wait.

[Anonymous Coward]

Sure, 1ton = 1000kg
Why do you ask?

Re:Just wait.

[m50d]

I think it's getting there. As a product of this schooling, I'm mentally fluent in both systems of weight, and that's only because of cooking with my mother. Ask me how long something is and I'll tell you in metres. To me 70 degrees is the temperature of a cup of tea. It will take time, sure. But the switch is happening. Half of my class didn't know how many pounds there were to a stone.

Re:Just wait.

[Guppy06]

"As far as I know, one litre is 1000 cm^3. How did you think it is defined? Perhaps you are thinking of the old definition of a kilogram?"

Originally, the liter was defined, as you said, as 1 dm^3 ("one cubic decimeter"), and the kilogram was defined as 1 L of water at X, Y, Z temperature, pressure and gravitational acceleration. Then, things were swapped: when the current iridium-platinum kilogram definition was introduced, the definition of the liter changed to "1 kg of water at X, Y, Z temperature, pressure and gravitational acceleration." This worked out to be around 1 L = 1.000028 dm^3 or so. It was only in the Twentieth Century that it was changed back to 1 L = 1 dm^3.

Re:Just wait.

[bash_finger]

from 'Machinery,s Handbook Revised 21st Edition'
Library of Congress Catalog Card Number: 72-622276

Page 2408

"Standard of Length. In 1866 the United States, by act of Congress, passed a law making legal the meter, the only measure of length that has been legalized by the United States Government. The United States yard is defined by the relation: 1 yard = 3600/3937 meter."

Re:Just wait.

[Guppy06]

"Wrong, since 1964, a SI liter is:"

You missed the "over the past century" part. From 1901 to 1964, the liter was defined as "1 kg of water at X, Y temperature and pressure" During this time, 1 L was about 1.000028 dm^3 (where dm = 10 cm = 0.1 m). Before 1901, it was, as you said, 1 L = 1 dm^3 exactly.

"I would say it makes more sense than a random 231 quantity,"

It was originally defined by the volume of a cylinder of given dimentions, but Congress decided to round off to the nearest cubic inch in the 1800's or so. It may be a relatively arbitrary number, but it is far simpler to realize (if not more realistic) than trying to recreate a sample of water of acceptable purity while trying to juggle the related qualities of temperature and pressure while trying to account for differences in gravitational acceleration on an inconsisten, spinning globe*, which is what both the liter (1 kg H2O) and the UK gallon (10 lb H2O) used to be defined as. There are reasons why that idea was dropped like the bad habit it was, and both are now defined with respect to the meter, just like the US gallon has been since the 1890's.

The only real change to the US gallon came when the US inch itself was changed, from 100/3937 m to 0.0254 m. Cube the difference between those two numbers and you'll see that the change in the US gallon is downright negligible, especially when compared to the change in the liter from 1 dm^3 to 1.000028 dm^3 and back. With the liter, in a technical capacity, you need to worry about what year the measurement was taken. There's no such problem with the US gallon.

* The atmosphere is a fluid. If you're not comparing your sample of water to your metal mass definition in a complete vacuum (which, since we're talking liquid water, would be more or less impossible), you have to take into account that the water is more buoyant (weighs less) in the atmosphere than X/Y ratio platinum-iridium alloy. Not to mention, buoyancy is affected by weight while pressure is affected by mass, so you need to worry about differences in local gravitational acceleration. This episode of Sesame Street is brought to you by the numbers 101.325, 277.13 and 9.80665.

(BTW, because I have absolutely no life, I sat down once with some steam tables and played with the original definition of the UK gallon before they, too, went metric and pegged it to the meter. At the temperature and pressure the water was supposed to be measured at, the volume they came up with is just flat-out wrong. There are reasons why the US was among the first to jump ship from UK standards, and the only problem it caused is that, because we were the first to abandon the shrinking yard, our yards/feet/inches were a little longer than the yards/feet/inches everybody used until we all standardized on a metric yard in 1959.)

Re:Just wait.

[Luchio]

Road planning and surveying are mostly done in metric internally, and converted for public information. I've heard about one law that says no speed limit sign may be posted in metric, which is understandable, 60 MPH is about 100kph. Some jerk could just see the 100 and speed on his merry way as if it were MPH.

When we changed from the British system to the metric system here in Canada, my father used this to his advantage during the first few years after the change. He always told police that he thought the sign was in MPH so he wouldn't get a ticket!

That's been over 20 years that Canada adopted the IS, so now he has to pay for the tickets...

Re:Just wait.

[surprise_audit]

I always though that was a scam worked on the American public by various supply companies. A US gallon is 3 imperial quarts, so for every 3 imperial gallons imported, they get to sell 4 US gallons.

Re:Just wait.

[AndrewJ-NYC]

I'm reminded of the (apycryphyal?) story I heard about why they continute to drive on the left in India. Apparently they wanted to switch to driving on the right when they became an independent country, as part of ditching the colonial legacy--only to realize that the tens of millions of bulls and horses used to haul wagons were so stubborn as to make it impossible to retrain them to use the other side of the road. Sometimes, the most mundane of practical considerations can carry the day.

Re:Just wait.

[jerde]

> If he meant Burma, he really meant Myanmar (aka the country formerly known as Burma)

Not so much.

The United States officially does not recognize "Myanmar" as the name of that country, instead continuing to use the official name of "Repulic of Burma" adopted by their former, democraticly elected, government.

(see wikipedia article)

- Peter

Re:Just wait.

[Guppy06]

"How about the fact that virtually the entire world uses the metric system?"

A lot of people around the world speak English. Does this mean governments should work to actively suppress indigneous langauges in favor of it?

"And with today's shrinking village of a planet every year that the U.S. sticks to the imperial system is costing tons of money in conversions, separate sets of tools and machine parts,"

The same can be said for instruction manuals in six or seven different languages, if not more so; the relationship between inches and milimeters is defined and exact, unlike the vagrancies of language. The fact that the relationship between the two units is exact means there is little problem in finding tools in both sets of units. Metric-only China has no problem manufacturing inch wrenches and sockets once you give them the CAD/CAM file.

And as for the people that use those tools you mentioned, can't find a 1/2 in socket? Try the 13 mm. Anybody in the US that actually uses those tools on a daily basis knows things like that, and finding a mechanic that speaks both inches and milimeters is a lot easier than, say, finding a mechanic that speaks both English and Spanish.

"Finally let me give you a simple example of how convenient the metric system is:"

What you describe isn't "the metric system" and it sure as heck ain't SI. It is, instead, metric(ation) mythology which is, to be blunt, flat-out wrong.

"One liter of water at sea level and room temperature weighs 1 kilogram."

Using the current definition of 1 L = 1 dm^3, you cannot, in any way, shape or form, get pure, liquid water to be 1 kg/L at 101.325 kPa (CGPM's definition of "1 atmosphere"), ever. It is physically impossible. At it's absolute densest at around 277.1 K, you can get it to 0.999972 kg/L, but that's it. Under an older definition of 1 kg, you could get 1 kg/L, but that hasn't been true since 1901.

On the other hand, at approximately 372.8 K (a few dK shy of boiling), you can get liquid water to be 1 ounce per US fluid ounce. Meanwhile, the only people who win on the whole 1/1 ratio for the density of liquid water at anywhere near room temperature are the British, who get 1 oz/(fl oz) at around 294.2 K, while the generally accepted number for "room temperature" is 298.15 K.

"Water boils at 100 degrees Celsius"

At 101.325 kPa, water boils at 373.124 K, which, while close, is not the same as 373.15 K.

The degrees Celsius temperature scale is closely related to the degrees centigrade scale, but they are not the same. The boiling point of water at 101.325 kPa "just happens" to be near 373.15 K, just as the freezing point "just happens" to be near 273.15 K, but those numbers are not incorporated in the definition of the modern degrees Celsius temperature scale. The only property of pure H2O set in stone is the triple point, defined to be 273.16 K (or 0.01 degrees Cellsius, if you will). Everything else is a series of arbitrary decisions to try to make the measurements fit the model.

"Now you tell me, quickly, exactly and off the top of your head, how many inches in a foot? How many inches in a yard? How many yards in a mile?"

12, 36 and 1760. Also, off the top of my head, I can tell you that there are 220 yards in a furlong. Moving on to what I'd have to use math for...

"How many inches in a mile?"

Of what possible utility is that conversion? My car's odometer may measure in miles and there may be an exact integer number of inches in a mile, but that doesn't mean my odometer will tell me how many inches (or feet or yards) my car has driven to any meaningful accuracy, just as a metric odometer won't tell you if your car has moved 1 m since you last read it. Measurement isn't about conversions, it's about accuracy and signifigant digits, and decimal conversion rules is a substitute for neither; it can actually be a problem if it gives you the illusion of ha

Re:Just wait.

[Anonymous Coward]

Actually, we don't use British/Imperial measures. We use English measures.

All U.S. units either date back to before the permanent dissolution of the English Parliament (the Queen Anne gallon, which became the U.S. gallon, was one of the last acts of that Parliament before the 1707 Act of Union), or were established by the government of the U.S. We never used the British Parliament's Imperial System, which didn't come into effect in the British Empire until 1826, fifty years after we'd declared independence from the British.

Similarly, our colonies were created by the English, not the British; our spelling is perfectly acceptable by the standards of pre-British English; and the part of the world with an accent closest to that of the London of Shakespeare and Elizabeth is, believe it or not, New Jersey. (The "Shakespearean accent" is a wholly British invention.)

Oh, and the U.S. Bill of Rights? Derived from the English Bill of Rights. Which the British ignore; what does the British parliament care that the English Parliament secured the people of England the right to have arms for their defense? Why, no more than they cared for the rights of the people of the colonies, China, India, or Africa.

So it's no wonder that, as the true heirs of the free English, the U.S. continues to use English measures. It is merely a tragedy that England allowed itself to forget its heritage and became part of the rights-abusing imperialist Britain of the Intolerable Acts, Opium War, and conquests of India and Africa. It is that imperialist people that invented the Imperial System, long after the United States won its independence.

Re:Just wait.

[Anonymous Coward]

Moving away from 'golden samples' to physical-constant based measurements (you might have noticed the topic of this very discussion) is what they mean by "improving, extending and revising."

So apparently the author is a "real American," and now I can't tell if you were trying to insult or compliment the US.

Re:Just wait.

[Mad Marlin]

That is actually one of the weirdest road signs I have ever seen: On I-44 Eastbound on the way from Rolla (home of a good engineering school and not much else), there is a mileage sign saying St. Louis ??MI 100KM (can't remember how many miles, if I remembered my basic engineering stuff I could figure it out). That is the only time I have seen metric on a US road sign, only that one sign. It's still there.

Re:Just wait.

[tverbeek]

Sorry, Steve*, but the U.S. State Department isn't actually the final authority on what other countries are named. That's generally up to the governments of the countries in question (legitimately elected or not). Furthermore, the one external body that might be considered a legitimate arbiter of the question - the U.N. - accepts "Myanmar".

*That's what I've decided your name should be.

Re:Just wait.

[njh]

Here in .au a pint of beer is defined as 600mL I think. We still call them pints, pots, schooners, yards, carafs etc. :)

Re:Just wait.

[28481k]

400 grams of turkey is of course more than enough for a meaty sandwich, but should be less than enough to feed a family for a week. We used to have turkey sandwich for breakfast, and we bought them by pounds, in a family of 4 we finished them in 5 days at most.

Incidentially, in Hong Kong, we essentially got three measures:Imperial system, metric system and Chinese system. We use metric totally for volumes and distances, but not for weights. We normally weigh ourselves in pure pounds (as in US usage) and measure our height in feet and inches (though the teenagers do use metric). We bought food in pounds or catties (a Chinese unit which is based on Imperial pound, 1 1/3 pound equals a catty), and bought flats/apartments in square feets. Petrols are sold in litres (and it's extremely expensive, second to the UK!). Jewellers use Chinese weight system as well. That's a whole lot of confusion and makes the metric law almost impossible to enforce. Hence, the government didn't bother at all, and even supermarkets sold fresh produce in Imperial system!

In China they use metric, but they still got their odd inches (1/30 of a metre) and there's a convient measure of catty in half a kg, so when we go across the border to shop we have to be vigilant about the measures!

Re:Just wait.

[28481k]

Haha, you reminded me, when we get a temperature, we always measure them in Fahrenheit, and recorded as such in medical records, though normally we use Celcius for other intended functions with an exception of oven of course.

OT: I think 70F is a bit too low for a unmilked cup of tea, for me, a cup of tea needs to stay at least 30C/86F to be good to drink...

Re:Just wait.

[jazman]

Dead right. What kind of break from the past was that? They should have stopped speaking English as well (no, pronouncing all vowels as "a" or "aya" doesn't count, as in the disaster movie phrase "Aah maah Gayad, waah ganah daaaaaaaah"). In fact why stop there? I see Americans' body chemistry is still derived from the English, so not only should they rewrite their DNA they should also stop using DNA completely!

Re:Just wait.

[TheEnglishPatient]

And our language, although you have bastardised it considerably

Re:Just wait.

[m50d]

Well, my oven works in celsius, I could tell you to cook cakes at 170 (fan oven, 180 for a normal one) and wouldn't have a clue in fahrenheit. But I think temperature is one place where the metric version is obviously far more logical, wheras that isn't so much the case for other units, so switching wrt temperature is easier.

Re:Just wait.

[28481k]

Well, my oven works in celsius, I could tell you to cook cakes at 170 (fan oven, 180 for a normal one)...

Sorry, m50d but I think I made a mistake just now because I always thought oven runs at a lower temperature than things like 170C so I thought it was in Fahrenheit. However, I did a little research for oven temperature details, and I can solemnly tell you that most oven do run in Celcius. (grumble... :P)

http://www.hintsandthings.co.uk/kitchen/oventemp.h tm

artifact

[whathappenedtomonday]

is the only one of the seven basic units of the international measurement system defined by a physical artifact

hm, don't think so:
what about the meter?

Re:artifact

[rokzy]

the 'meter' isn't a unit. perhaps you're thinking of 'metre'?

Re:artifact

[thebes]

Wrong: On October 20, the meter was redefined again. The definition states that the meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. The speed of light is

c = 299,792,458 m/s

This

It's true that it was once defined that way, however, it has been redefined.

Re:artifact

[damian cosmas]

how, exactly, is the speed of light in a vacuum a physical artifact?

If you're referring to the 133Cs, it obviously decays with time, making it a rather poor physical artifact.

Re:artifact

[Anonymous Coward]

In 1960 the meter was redefined as 1,650,763.73 wavelengths of orange-red light, in a vacuum, produced by burning the element krypton (Kr-86). More recently (1984), the Geneva Conference on Weights and Measures has defined the meter as the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock which emits pulses of radiation at very rapid, regular intervals.

Maybe you should read the pages you link to?

Re:artifact

[FooWho]

From the article you linked...

More recently (1984), the Geneva Conference on Weights and Measures has defined the meter as the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock which emits pulses of radiation at very rapid, regular intervals

Re:artifact

[Anonymous Coward]

In 1960 the meter was redefined as 1,650,763.73 wavelengths of orange-red light, in a vacuum, produced by burning the element krypton (Kr-86). More recently (1984), the Geneva Conference on Weights and Measures has defined the meter as the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock which emits pulses of radiation at very rapid, regular intervals.

They mean there isn't a stick of wood in a case somewhere labeled "meter" like the kilogram. A meter can be determined exactly over and over with the experiment.

Re:artifact

[lobotomy]

Did you actually read all of the article that you link to? The meter is currently defined (according to your link) as:

More recently (1984), the Geneva Conference on Weights and Measures has defined the meter as the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock which emits pulses of radiation at very rapid, regular intervals.

Thus, the meter is not defined by a physical artifact.

Re:artifact

[whathappenedtomonday]

no I'm not, I'm thinking of the standard meter which was the original "master" for all measuring back then. just click the link, I know you can do it.

Re:artifact

[JaxWeb]

Just in case people care, here are the 7 base units:

Metre for Length
Kilogram (what this article is about) for Mass
Second for time
Ampere for current
Kelvin for temperature
Mole for amount
Candela for "Luminous intensity" ... or something.

All the others are built up and defined from these, so these must be well defined. Change what exactly a Kg is changed more than just mass - it changes everything dependant upon it. Hence, these things must be got right.

The definition of second changes every now and then though, and I think the metre has changed a few times, too. I wrote a bit about the second here, in my AS-Level Physics coursework, if anyone want s a simplifed read.

(Wiki)

I don't see how this topics is maths, by the way.

Re:artifact

[bunnyman]

You forgot the CmdrTaco, the basic unit of redundancy.

Re:artifact

[Anonymous Coward]

The definition of meter, as well that of second
have been changed quite some time ago and they do not involve any human artifact:
http://physics.nist.gov/cuu/Units/curre nt.html
This has been done because the speed of light is constant. So, instead of measuring a constant in terms of units that were somewhat fuzzy (m and s), it is convenient to set the value of the speed of light and define the meter in terms of the second and the second in terms of a timescale associated to some nuclear decays (another constant).
Today the same problem arises with the Plank constant: why should we define it in terms of a fuzzy quantity like the kg? We know the Plank constant is constant, so let's set its value ad define the kg from it.
Notice that is very different than setting pi=3.
Constants like pi are the results of a computation and we do not have any freedom in changing their value. The speed of light, the plank scale and the gravitational constant are constants but their value is a human convention that is equivalent to choosing units of measure.

Re:artifact

[bunnyman]

Did you actually read that web page? It says the meter is defined as the distance light travels in a certain amount of time.

Re:artifact

[Yartrebo]

There are only 3 - maybe 4 - basic units - the metre, kilogram, and second.

Candela essentially measures the same things as watts.
Mole is just an number. It might be used in the definition of the kilogram, but in itself, it just relates the mass of a gram with 1/12 the rest mass of a carbon-12 atom.
Kelvin is just a unit derived from mass, momentum, and kinetic energy. It is not a base unit.

Ampere might or might not be a base unit, I'm not sure about that one.

Re:artifact

[Tomfrh]

The metre was once defined from a physical artifact, but it is now defined in terms of light.

Re:artifact

[JaxWeb]

It is well known there are 7 base units.

"Candela essentially measures the same things as watts."

But watts are not a base unit. A watt is the same "Joules per second", and Joules is also not a base unit, but is defined as a Newton Metre. But a Newton isn't a base unit, it is defined as a Kilogram Metre per second per second. So:

Newton = kg.m.s^-2
Joule = Nm = kg.m.s^-2.m = kg.m^2.s^-2
So a watt is in-fact a kg.m^2.s^-3 , or "Kilogram metre squared per second per second per second" - hence changed the kilogram will change the watt, despite them seeming unrelated!

A mole isn't the same as mass at all. It is more to do with things on an atomic level. It's really used in chemistry - I've personally never used it outside of a chemistry exam (or coursework). It is sort of just a number, but it actually isn't.

Kelvin is a fundamental base unit too. Momentum is defined as "Newton Seconds", and so (remembering the definition of a Newton) kg.m.s^-1. Kelvin's measures temperature, which is a measure of kinetic energy, so I can see where you are coming from. You're just wrong.

Ampere is too. Helpfully, from it you can define other helpful things like volts. A volt, for your interest, is defined as kg m^2 s^-3 A^-1 , or "Kilogram metre squared per second per second per second per amp". And so yet another thing this change would affect.

It's all very interesting.

Re:artifact

[Anonymous Coward]

In normal English (not American English), "metre" is the measurement, and "meter" is something which measures.

So there! =)

Re:artifact

[Yartrebo]

You just proved me right.

You just showed the candela is based on metres, seconds, and kilograms. Therefore it is not a base unit of its own.

Same goes with the mole (based on nothing - it's a scaler) and kelvin (based on metres, kilograms, and seconds).

A unit is only a base unit if it cannot be described using scalers and other base units.

Re:artifact

[Anonymous Coward]

"how, exactly, is the speed of light in a vacuum a physical artifact?"

It's not, it *defines* a physical artifact, abstractly.

Re:artifact

[Anonymous Coward]

I agree with you. The number of base units is a somewhat arbitrary choice of a unit system. Candela and Amperes are SI base units. If SI were defined differently, then there could be a smaller number of base units.

e.g., Define mu_0 as 4*pi * 1e-7 in units of "X".

Since 1948, the unit of current is defined as the amount of current which causes two parallel conductors one meter apart to exert a force of 2e-7 N per meter of length on each other.

To calculate the value of this current, using Ampere's law and the Lorentz force law, you only need to know the value of mu_0.

In the SI system, mu_0 is defined such that its units ("X") are Newtons / Ampere^2. So the units of current are Amperes.

But you could just as well take mu_0 to have some other dimensions. If you define mu_0 to be 4pi *1e-7 in units of Newtons * seconds^2, then electric charge will be dimensionless, and electric current will have dimensions of 1 / time.

Some unit systems even take mu_0 (among other fundamental constants) to be dimensionless and equal to 1. This is more convenient for manipulating equations, since you don't have to write so many conversion constants. But it is not as convenient for some everyday calculations, because you lose the error-correcting check of "has my answer got the right dimensions?".

Re:artifact

[Anonymous Coward]

A unit is only a base unit if it cannot be described using scalers and other base units.

No, you are wrong.

You agree that a second is a base unit in SI.

But a meter is defined as the distance travelled by light in vacuum during 1 / 299792458 seconds.

If your statement were true, then a meter could not be a base unit.

Re:artifact

[Anonymous Coward]

Candela and Watt are different though. They aren't the same as you think they are. I realise they are related, however. The Lux is defined in terms of the Candela (Being candela's per second). The Mole isn't quite a unitless. When they tell you that, they are lying. It is actually something, albeit something very arbitrary. That's why things are measured in moles. All base units are scalar. Also, a unit cannot be based on nothing. Being based on nothing does not mean it is scalar - that is not what scalar means.

Kelvin cannot actually be defined as you think it can. I'm can see where your logic is coming from, but given the length, mass and time you cannot easily come up with the Kelvin. The relationship is more complex than is allowed.

A unit is only a SI Base unit if SI said it is, so even if you were right, which your not, it is stupid, because this is just the way it is. Possibly if you designed the unit system, you could come up with something better. But you didn't so you haven't.

Posted anon (since it is unlikely to get modded up), but this is the parent.

- Jax.

Re:artifact

[barawn]

What you're talking about are "fundamental" units versus SI base units.

In a fundamental system of units, there are three base units: charge, mass, and angular momentum. (Gee, those sound suspiciously like the three properties that a black hole can possess - I wonder why). Everything else can be derived from those units (for the most part - we'll ignore stuff like baryon number, lepton number, etc. because those theories aren't complete yet. For instance, we now know that only global lepton number is conserved, not mu, e, and tau lepton number separately. I won't even touch color, as color is completely hidden anyway).

In fact, the existence of those units can be derived from the fact that space is invariant under the Poincare group, and has gauge symmetry.

However, those base units come because you've defined other constants to 1.

The problem is that several of those constants are imprecise and difficult to measure. It is easier to define a kilogram, for instance, then it is to somehow base it on the gravitational attraction of two objects, because G is horribly imprecise.

Similarly, it is easier to treat Kelvin as fundamental rather than derived from other units *if* Boltzmann's constant has poor precision.

So while it's *possible* to use fundamental-based units, it's often *impractical* and less precise. The base units in SI are those that can generate all other units with no loss in precision.

To give a very practical example, the mass of a proton is typically given in atomic mass units (amu) as ~1.007 amu. You might think that it should be given in grams, as "amu" isn't a fundamental unit of mass. But the conversion from "amu" to "grams" is less precise than the mass of the proton in atomic mass units. So in this case, "amu" would be appropriate as a base unit, as well as mass, even though the two can be directly converted.

The benefit is that you can compare the mass of a proton and the mass of a neutron in "amu", for instance, to better precision than you could in grams. It's similar (or was similar when SI was developed) with the other units.

Re:artifact

[Alsee]

A volt, for your interest, is defined as kg m^2 s^-3 A^-1 , or "Kilogram metre squared per second per second per second per amp".

It's all very interesting.

The truth of that statement is inversely proportional to the square of the distance from Slashdot.

-

Re:artifact

[barawn]

Candela essentially measures the same things as watts.
Mole is just an number. It might be used in the definition of the kilogram, but in itself, it just relates the mass of a gram with 1/12 the rest mass of a carbon-12 atom.
Kelvin is just a unit derived from mass, momentum, and kinetic energy. It is not a base unit.

Ampere might or might not be a base unit, I'm not sure about that one.

You are talking about base units of physics (and you're still very wrong there), not base units of measurement.

Take Kelvin, for instance. We'll ignore the fact that temperature really relates both energy and *fundamental statistics* (the temperature of a gas of fermions at a given temperature is different than a gas of bosons at a given temperature). But even if it didn't, and it was just "average kinetic energy over Boltzmann's constant", you could say that Kelvin is just inverse joules...

if you set Boltzmann's constant to 1, and have it be unitless. The problem is that you've now shifted any imprecision of measuring Boltzmann's constant into *all measurements of temperature*, rather than just keeping it in the connection between energy and temperature. So when you calibrate your new temperature scale in "inverse joules", you now face the same precision problems that you would face in measuring Boltzmann's constant. That is, you have to measure the average kinetic energy of an ideal gas, and label that on your "inverse joule" thermometer.

This is dumb. Of course, what you do is use Kelvin as a base unit, and *define* the scale using other processes (the triple point of water, if memory serves) and now you've got a perfectly calibrated scale to huge precision, and the only imprecision from measuring the Boltzmann constant comes when you want to convert to energy.

So, again - base units of measurement are not the same as base units of physics. The base units of physics are the fundamental quantum numbers of a particle, mass, charge, spin (and color). The base units of measurement are the SI units.

Re:artifact

[Anonymous Coward]

you can derive the kinetic energy of a atom or molecule of gas, given basic assumptions about momentum etc.. then you make some wild ass assumption that its energy is going to eqi-partition between all its modes of vibration and rotation etc ... cause of the statistics of a large number of particles (valid for gas) Now the temperature is related to the PV=nrt and PV^gamma = const for adiabatic processes. so yeah for sure you can relate the temperature and energy of a particle of gas. also doesnt the 'gibbs energy' and entropy come in about here.

Q to the sl4shb0ts >>> w0t is the units of entropy.. chew on that one will yah !!

Re:artifact

[Anonymous Coward]

You're being a bit sketchy - read this post - he said it better than I could.

Entropy, as you know, is Joule's per Kelvin. I defined what a Joule is a couple of posts ago - it ended up to be kg m^2 s^-2. Thus Entropy is kg . m^2 . s^-2 . K-1, or "Kilogram metre-squareds per second per second per kelvin".

- Jax (A/C)

Re:artifact

[hankwang]

Candela essentially measures the same things as watts.

The candela is a weird unit, but it is not equivalent to watts. There are three units related to light:

• lumen -- comparable to watts, but weighted with a defined sensitivity curve that is supposed to represent the response of an average human eye;
• lux -- lumens per square meter
• candela -- lumens per steradian (unit of solid angle). It represents brightness, i.e. how bright the light source looks if you look into it from a specified distance.

For some reason the candela was chosen to be the base unit, rather than the lumen; probably because it is easier to calibrate for. The sensitivity curve is rather arbitrary. It is fundamentally impossible to measure this curve with high precision since individual humans are different and it requires test persons to judge subjectively whether, say, a red and a green light source are equally bright.

Since these units are defined to some hard-to-measure property of the human body, I think they shouldn't have a status as an SI base unit. Inches and feet don't have that status either, after all.

Re:artifact

[Anonymous Coward]

So you're saying that the big woman buying all the twinkies at the store yesterday was a high voltage device? And she was simply trying to increase her voltage further?

A volt, for your interest, is defined as kg m^2 s^-3 A^-1 , or "Kilogram metre squared per second per second per second per amp". And so yet another thing this change would affect.

Re:artifact

[Anonymous Coward]

Your definition of normal is off. More than 3/4s of English speakers are American. The Commonwealth is cute and all, but you guys need to get to fucking if you think your shitty spelling needs to be spread around some more.

Or will you try to justify spelling it nothing like it sounds?

Re:artifact

[Jamu]

It's not: It's based on the second. 1 meter = 1/299792458 seconds

Re:artifact

[jazman]

Shorly yoo meen "Or wil yoo tri tu justifie speling it nuthing like it sownds"

that does it

[WormholeFiend]

I'm going back to pounds and stones.

Re:that does it

[zxnos]

yeah, My car gets 40 rods to the hogshead and that's the way I likes it!" -Abe Simpson

(504 gallons per mile)

Re:that does it

[tehshen]

Sadly, both pounds and stones (and all masses thanks to the SI system) are based off kilograms.

1 pound is 453.59 grams
1 stone is 6.35 kilograms

Something like those, anyway. So going back to pounds and stones won't help you, I'm afraid.

Re:that does it

[thebes]

How could a stone, which was around before the kilogram, be based off the kilogram?

Re:that does it

[tehshen]

Of course they were not based off the kilogram *originally* but if you look anywhere, you'll find their value in kilograms. I couldn't find how their original value came about.

Re:that does it

[Gabrill]

that's because the original definitions were converged from many similar measurements, like the yard was. If memory serves, the yard was the distance from your nose to the tip of your outstreched finger. If you needed more accuracy, it was the distance from the King's nose to the tip of His finger. The actual physical measurements weren't standardized until relatively recently, but the rough measurements were good enough for trading, most of the time.

Re:that does it

[Dwonis]

You mean 504 miles per gallon...

Re:that does it

[ZeLonewolf]

No, you moron, it's gallons per mile. That's why the quote is so ridiculous. A hogshead is a large volume...essentially it's a large wine cask. So, imagine only going 30 rods on a LARGE cask of gasoline. A rod also happens to be an impossibly short distance, at least in the sense of automobiles.

Now, it so turns out that the hogshead is a different volume depending on whether it's a wine hogshead or a beer hogshead. Further elaboration on this, as well as a calculation of the other possible conversion of 30 rods/hogshead, is left as an excersize to the reader.

Re:that does it

[Anonymous Coward]

boo google calculator doesn't have a hogshead conversion.

Re:that does it

[rob_squared]

I *really* don't want to explain how much I weigh in slugs though.

Re:that does it

[Anonymous Coward]

Strangely enough, Australia uses metric units almost everywhere, but weights are still often measured in stones (particularly for people's weight).

I guess "10 stone" sounds better than "63 kilos", and it takes an awful lot of food to put on a stone, so people can claim that they haven't put on weight because they are still "10 stone".

International = 60% US scientists

[Anonymous Coward]

outnumbering the other members 2 to 1
good to see things "fair and balanced(TM)"

Re:International = 60% US scientists

[TheKidWho]

Hrmm interesting... Maybe this will be one of those situations where the US started off ahead with the imperial system, then the Europeans got their more advanced and scientific metric system but the US was slow to adopt the standard. And then the US switches over to a new even more scientific system but the EU stays with its backwards "metric" system.

Re:International = 60% US scientists

[TheKidWho]

Of course I hadn't RTFA article yet, so what I just said above is idiotic...

Re:International = 60% US scientists

[Anonymous Coward]

what you said was idiot regardless of whether you'd read the article or not.

Re:International = 60% US scientists

[Anonymous Coward]

Well surely you understand that it is indeed the metric system that is to be updated, not totally replaced by something else.

And in other news...

[rollingrock]

Pi is exactly equal to 3!

Re:And in other news...

[bobscealy]

Pi is exactly equal to 3!

You're an engineer, right..?

Re:And in other news...

[Anonymous Coward]

For very large values of 3?

Re:And in other news...

[Anonymous Coward]

In 1897 the General Assembly of Indiana, USA enacted in Bill No. 246 stating that Pi was de jure 4.

Re:And in other news...

[Gabrill]

No, only moderately large values of 3.

Re:And in other news...

[Talez]

<Frink> PI IS EXACTLY 3!
*Gasp from scientific community and silence*
<Frink> Sorry it had to come to that people.

Re:And in other news...

[rob_squared]

That's about right, give or take .1415926...

Re:And in other news...

[ScytheBlade1]

Informative? What are you smoking?

Can you say "Hello Simpsons quote"?

Re:And in other news...

[stormi]

i thought it was the square root of ten

Re:And in other news...

[KristoferP]

And suddenly all circles became spirals

Re:And in other news...

[sql*kitten]

Pi is exactly equal to 3!

My brother is a scientist. I had just gotten a new phone, so he didn't have the number, and I texted him to say "Pi is exactly 3". He send back several long messages explaining why this wasn't true, as far as he knew to a complete stranger. So either scientists are incredibly helpful people or they have way too much time on their hands...

Re:And in other news...

[line.at.infinity]

Well if you take a diameter of about 3844 km (30% of Earth's diameter) on the curved surface of Earth, then the ratio of circumference to diameter would be about 3 (according to my calculations).

Re:And in other news...

[btlzu2]

AH HA!!! You're still around. Cool. Was looking for new JEs! :)

Glad to know you're ok.

The last time this was mentioned

[tepples]

You might find some additional background information about this effort in an earlier Slashdot article about this topic, posted in May 2003.

How about

[TheKidWho]

Replacing the second while your at it, and the meter! Units based off of the earth.

Re:How about

[be-fan]

The second and the meter have long since been based off of more fundemental measures. The second is defined as how long it takes for 9,192,631,770 cycles of microwave light to be emitted by the hyperfne transition of cesium-133 atoms. The meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.

Re:How about

[Anonymous Coward]

Not any more.

Re:How about

[Anonymous Coward]

I don't mean to sound like an idiot, but since the meter is based on a second, how is it still a fundamental unit?

Re:How about

[Anonymous Coward]

Because you can still regenerate it from physical principles without relying on some arbitrary object (ie the random platinum rod that used to define a meter).

Re:How about

[Anonymous Coward]

Because he's wrong. The modern definition is "1650763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the krypton-86 atom".

Re:How about

[rob_squared]

I think he meant how it is only useful for earth, how many planets on star trek have 24 hours in a day, or 365 days in a year? That's the kind of "arbitrary" he's talking about.

Re:How about

[be-fan]

You sure? The NIST still has the definition in terms of the distance traveled by light: basic units.

Re:How about

[Anonymous Coward]

Also, the cesium atom is understood to be at 0 K to eliminate interference.

oh well...

[tverbeek]

So I guess this means that my suggestion to have the kilogram redefined as (my body mass/90) has been rejected?

Re:oh well...

[Anonymous Coward]

Yeah, it was rejected, but after seeing the picture attached to your application, they are considering redefining the metric ton to be your body mass/90.

Re:oh well...

[rob_squared]

about 200 lbs? that's about average i guess

Redundant definition?

[Resound]

I thought one cc of water weighs one gram. Thus one litre of water weighs one kg. Am I wrong? This would certainly satisfy the criteria of natural phenomena vs. artifact, although I suppose that definition gets a trifle fuzzy when we start talking about measurements like picograms.

Re:Redundant definition?

[Anonymous Coward]

That what I was taught in grade school and university. This is the first time that I've heard a kilogram being linked to iridium plates

Re:Redundant definition?

[be-fan]

There are a couple of issues here. First, one liter of water at what temperature? Water does expand slightly as temperature increases. Second, how accurately can you measure one liter? Lastly, one litre of water doesn't weight exactly a kilo, it's like 0.99998 kilos.

Re:Redundant definition?

[WormholeFiend]

although I suppose that definition gets a trifle fuzzy when we start talking about measurements like picograms

Picograms are important when you mesure LSD doses.

Re:Redundant definition?

[darkmeridian]

Sure, a gram is defined by a volume of water at a certain pressure and temperature. However, this is impracticable in many settings. Water changes density very readily. It is much simpler to define a gram in other terms that is close enough to the 1.0 g/1.0 ml H20 yet still is stable enough to use in experiments. From the article:

For instance, it would improve the precision of certain electrical measurements 50-fold and would enable physicists to make more precise calculations in studying the fundamental quantum properties of atoms and other basic particles. The paper outlines how this could be accomplished without impairing the current international system of mass measurements.

Re:Redundant definition?

[the eric conspiracy]

I thought one cc of water weighs one gram.

This is so wrong on so many levels.

- A gram is a unit of mass, not weight.
- One cc of water can contain any number of water molecules depending on temperature and pressure, so who can say what its mass is without this information.
- How much something weighs depends on the local gravitational constant which is different from one place to another.

So I think I can say that it is very unlikely that one cc of water weighs one gram.

Re:Redundant definition?

[Elgreco1]

Amm ... 1cc of water depends on temperature
The the weight depends on atmospheric pressure
given water can evaporate. Not a very accurate base.
In fact you are saying nothing diferent to x number of water molecules. Water waould be a bad choice

Re:Redundant definition?

[LDoggg_]

1 newton atmospheric pressure.
4 degrees centigrade.

AKA STP(standard temperature and pressure)

High school physics.

Re:Redundant definition?

[Fnkmaster]

We generally use the verb "weigh" to express units of mass, because there is no commonly used verbal form for mass. There is nothing inherently wrong with this, it's just a vagueness in the meaning of the word "weigh".

See NIST Special Publication 811 (1995 ed.), _Guide for the Use of the International System of Units (SI)_ by Barry N. Taylor (NIST is the National Institute of Standards and Technology, the successor agency to the National Bureau of Standards):

In commercial and everyday use, and especially in common parlance, weight is usually used as a synonym for mass. Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of".

Examples: the child's weight is 23 kg the briefcase weighs 6 kg Net wt. 227 g

Re:Redundant definition?

[Resound]

The temp and pressure issues are what I was thinking of when I said that it's a fuzzy value, these would need to be rigidly defined. I realise that tricky with pressure if you're to avoid a circular definition. Weight vs. mass is nit-picking, at least in this instance. If something weighs "a gram" in common parlance then it masses a gram.

Re:Redundant definition?

[kryptkpr]

Standard Temperature and Pressure?

273.15 K (or 0 C) and 1 atmosphere (or 101.325 Pa, or 760 mmHg)

Re:Redundant definition?

[nate nice]

"Picograms are important when you mesure LSD doses."

Nah, just add room temperature water to your volume of LSD creating a 25/1 ratio of water to LSD. Make sure it's stirred well and then apply to whatever medium you want (paper, sugar, gum, etc).

Now you can just dip your medium into your solution and viola! :P

Re:Redundant definition?

[ptarjan]

This is true but at what pressure? Under less pressure, water will expand and take up more room but still weight the same. The current model uses STP (if I remember corretly) which is an arbitry definition based on normal conditions at sea level on earth.

Re:Redundant definition?

[LDoggg_]

err.. 1 atmosphere, not 1 netwon.
Its been a while since high school :)

Re:Redundant definition?

[desenz]

I think STP is actually 1ATM, and 0 degrees centigrade. 4 degrees is where water is most dense, I think.

Re:Redundant definition?

[Anonymous Coward]

The difference between a Kg and a Newton is not nitpicky, in this instance, or ever.

Re:Redundant definition?

[iamlucky13]

To add to what others have said (it depends on temperature and pressure), it also depends on purity, and I'm almost positive, ever so slightly on ionization.

Re:Redundant definition?

[Jeremy Erwin]

No, STP is 1 atm at 273.15 Kelvins. Water is densest at about 4 degrees Centigrade.

I have always pitied you physicists, working in your frigid labs. We chemists prefered to keep our labs pressurized to 101 KPa and heated to 298.15 Kelvins.

Re:Redundant definition?

[the eric conspiracy]

because there is no commonly used verbal form for mass

There are at least two perfectly good ways of expressing this without incurring the incorrectness and ambiguity of 'weighs a gram'.

1. The mass of 1 cc of water is 1 gram.

2. 1 cc of water masses 1 gram.

As far as what the NIST says, that is baloney and an erosion of the precision of the meaning of words. That is extemely bad in this context.

Re:Redundant definition?

[Dun Malg]

Standard Temperature and Pressure? 273.15 K (or 0 C) and 1 atmosphere (or 101.325 Pa, or 760 mmHg)

Except that, as others have noted, one of the terms used to define "pressure" is mass. You must be able to substitute the formula for a kilogram in place of the kg term in any equation. A kg defined in terms of a kg then becomes recursive...

Re:Redundant definition?

[BigusDickus]

So how come if you go to Europe and step on a scale, it tells you you weight in kilograms. Why not in newtons?

Re:Redundant definition?

[dont_think_twice]

As far as what the NIST says, that is baloney

I had been wondering if NIST was just pulling these so-called standards from their ass. I am glad you confirmed it. From now on, a kilo is the amount of coke a mexican hooker can snort in one week. Or course, that is under STP.

Re:Redundant definition?

[Grishnakh]

There are a couple of issues here. First, one liter of water at what temperature? Water does expand slightly as temperature increases.

Huh? Yes, water does change in volume with temperature, but mass stays the same (as long as you prevent any water from vaporizing). A specific number of atoms will always have the same mass, regardless of temperature. However, because of the vaporization problem, using water to define the Kilogram probably isn't a very practical thing to do.

Re:Redundant definition?

[arodland]

and 1 atmosphere equals what? 101325 kg / m s^2, of course.

Re:Redundant definition?

[Fnkmaster]

I nominate you for post of the week. Seriously, I just snarfed my dinner.

Re:Redundant definition?

[Grishnakh]

As far as what the NIST says, that is baloney and an erosion of the precision of the meaning of words. That is extemely bad in this context.

It's not an erosion in the precision of words, simply because there never was any precision there to start with. The English language never had a verb for finding the mass of something until recently, when people started measuring masses instead of forces (weights) (except in the USA, where we stubbornly stick to pounds).

Even worse, "weighs" is actually more accurate in practical terms. Suppose you're in a lab (where you're actually using SI units), and you have a sample that you need to find the mass of. What do you do? You put it on a scale, which gives you a reading in grams. Did you just "mass" that sample? NO. You weighed it. This is because you didn't even measure its mass; you measured its weight: the force that it presses downwards onto the scale with because of gravity. The scale only reads in grams because it's been calibrated to translate the force (weight) measurement into mass, by assuming a fixed value for gravitational force. Of course, if you take that scale to a different place on the planet, or especially to a different altitude, it will read mass incorrectly until it has been recalibrated for that place. A scale that simply measures weight would not need any recalibration, because a pound (or a Newton) is the same no matter where you go.

This lack of precision in words is similar to the Free software movement's complaints about the word "free". When you say "free", do you mean "libre" or "gratis"? They're entirely different things, but our crappy language doesn't differentiate. But you can't say that anyone is "eroding the precision of the meaning of words" by saying "free", because our language was imprecise to begin with.

Re:Redundant definition?

[drinkypoo]

P = F / A

Re:Redundant definition?

[drinkypoo]

Yes, and a liter is a measurement of volume...

Re:Redundant definition?

[the eric conspiracy]

You put it on a scale, which gives you a reading in grams. Did you just "mass" that sample? NO. You weighed it. This is because you didn't even measure its mass; you measured its weight: the force that it presses downwards onto the scale with because of gravity. The scale only reads in grams because it's been calibrated to translate the force (weight) measurement into mass, by assuming a fixed value for gravitational force.

Poppycock. F=mg. The calibration establishes the value of g because the scale determines F and you inform the scale what m is by setting the calibration controls to that mass. Adjustment of the calibration sets the value of g at the location of the scale. When you then place another sample on the scale the computation based on the calibration returns the value of the mass using F=mg. Yes, internally the scale uses gravitational pull to detect the mass, however that is only PART of the measurement process. The entire process includes the determination of g so that you actually measure the mass. This is why the display on the scale says grams and not Newtons.

Re:Redundant definition?

[Anonymous Coward]

Yes, water does change in volume with temperature,

Which means that one liter of it (the liter is a measure of volume) will change in mass.

Re:Redundant definition?

[Grishnakh]

Yes, as I already pointed out, you have to calibrate the scale for your specific location. As soon as you move it somewhere else, or the continents move, or the gravitational force changes for some unknown reason, the scale is no longer accurate.

While the scale is giving you a reading in grams, the scale in reality is measuring force. It is only calculating the mass from this measurement. It is not measuring the mass directly. So if you place a sample on a mass scale, you are, in actuality, weighing (finding the weight of) it, which was my whole point. So, using the term "weighing" is actually correct.

As far as I know, there is no known way to directly measure mass, so even now we don't really need a verb for it.

Re:Redundant definition?

[Anonymous Coward]

And how do we define force? F=MA. Notice the M.....

Re:Redundant definition?

[Anonymous Coward]

How bout doing this in vacuum at 0 C?

Re:Redundant definition?

[Anonymous Coward]

Yes but we want to define 1 KG as the mass of 1 L (i.e 1 dm^3) of water. I.e volume is an issue

Re:Redundant definition?

[Alsee]

Or course, that is under STP

Won't work, your refference subject is going to be far higher than sea level.

-

Re:Redundant definition?

[drxray]

In zero gravity conditions, you measure the mass of* something by attaching it to a spring and measuring the frequency of oscillation. This measures mass directly, not weight. You can obviously do it under gravity as well (watch fat people bungee...), it's just less convenient than using scales.

*ironically, given the discussion, I wrote "weigh" here when I first wrote this...

Re:Redundant definition?

[dont_think_twice]

Okay, at STHAAK (Standard Temperature, High As a Kite) then.

Re:Redundant definition?

[magefile]

We generally use the verb "weigh" to express units of mass, because there is no commonly used verbal form for mass.

While you are correct that the verb "weigh" is often used that way, the *proper* verbal form for mass is mass, as in, "Go mass that platinum-iridium sphere for me".

Re:Redundant definition?

[be-fan]

That's exactly my point. If you define a kilogram to be a liter of water, you have to define it to be a liter of water at a certain temperature. A 1 liter container holds more water at 1-degree C than at 25-degrees C.

Re:Redundant definition?

[be-fan]

You should have paid more attention in high-school. STP is 101.325 KPa and 0C. Beyond that, KPa is a defined unit that uses mass in its definition.

Re:Redundant definition?

[LDoggg_]

yeah... well at least I got the term STP right :)

Re:Redundant definition?

[Anonymous Coward]

One cc of water can contain any number of water molecules depending on temperature and pressure, So I think I can say that it is very unlikely that one cc of water weighs one gram.

One gram of was first defined as one cm^3 of water. A standard of distance that converts directly to a standard of volume that converts directly to a standard of mass was the whole intent of the French. Sure water 20c and 1 atm has a density of .99821g/ml but when it was defined in the first place no one gave a shit. It wass accurate with in about .2% at tempratures where water is water and not ice or steam.

Re:Redundant definition?

[Cska Sofia]

Sadly, despite placing said artefact inside three of the strongest vacuum cylinders, the measure rapidly decayed to zero.

Re:Redundant definition?

[vidarh]

Because most of us are unlikely to use those scales somewhere with a different gravitational constant, seeing as the personal spaceships we've been promised by scifi writers still haven't materialised, so nobody really cares that they're really measuring something else that just happens to be equivalent in all the places they're likely to measure it.

Re:Redundant definition?

[Anonymous Coward]

The definition might be redundant, but you're certainly retarded.

Re:Redundant definition?

[Jim Starx]

That doesn't measure mass directly. It measures frequency directly. Then you use the constant of your spring to calculate mass.

Re:Redundant definition?

[blengino]

A specific number of atoms will always have the same mass, regardless of temperature.

No, it doesn't, as a mather of fact temperature is proportional to the kinetic energy (for instance the media of v^2, and since e = m c^2 if you heat a water container it will have more mass. If the people in the 1700's-1800's could measure mass as we can we might still have the theorie of heat as a fluid (in Spanish is called "calorico", I don't know the word in English).

Re:Redundant definition?

[stanmann]

so water at 25 to 1 of LSD applied to paper produces a moderately sized stringed instrument played with a bow?

Re:Redundant definition?

[Grishnakh]

WTF?? Either you better have some good support for this assertion, or you're totally full of it. I'll admit I'm not a physicist, but as a EE I've had enough science courses to understand the basics. Energy and mass are two different things. Heating stuff does not change the mass. It changes the kinetic energy, of course, as you're adding (thermal) energy to the system. (I'm assuming we don't lose mass to vaporization, etc.: a closed system not exposed to the atmosphere.)

Yes, E=mc^2, but that's only if you're causing a nuclear reaction. As far as I know, nuclear reactions and radiation are the only ways to convert mass to energy or vice versa. Heating some water doesn't cause fission or fusion, and I'm also assuming pure H20, so we can neglect any effects of any radiation from other isotopes that are normally present in regular water.

Re:Redundant definition?

[BigusDickus]

Exactly my point.

Re:Redundant definition?

[blengino]

Well lets take it by parts as Jack says ;)

I'm a physicist, not a very good one, but still ;)

The relation E = mc^2 doesn't asume anithing about the system, and it is the relationship between energy and resting mass (if you are traveling the mass may vary, the Lorentz factor strikes again).

The reason why it's used on nuclear reactions and other stuff like that is that there you can see a relativelly big change, on the every day things you can't. It's more o less like the use of the Lorentz relations to change the reference system betwen your car and the police oficer to see if you are speeding or not, its accurate, but useless.

I remember that the first example of the E = mc^2 thing was something like if I have a closed box with a resting ball and another closed box with a moving ball (providing that everything else is the same) the box with the moving ball would have a higher mass. I think that my teachers know about that better than you and me (I'm not making research on the relativity field, at least on of them where)

But again, I'm might be wrong, would be great to see a post from someone who is researching on the fiels

Re:Redundant definition?

[Grishnakh]

I think I remember this now... as an object's velocity increases toward lightspeed, its mass also increases. At lightspeed, its mass would become infinite.

But for most real-world things, isn't the mass change insignificant? i.e., heating up a cup of water

Re:Redundant definition?

[blengino]

Do you want a precise definition or do you not?

That's the problem. For everyday use the current definition is OK

Oh No...

[Anonymous Coward]

Please, don't tell us that it'll become 1024 grams!

Re:Oh No...

[Anonymous Coward]

No one's talking about a kibigram.

Re:Anyone Else?

[TheEternalVortex]

The SI unit of mass is the kilogram, not the gram.

Kilogram Scmilogram

[bigtallmofo]

I'm a little embarrassed that I still measure things in pounds, ounces, feet, inches, yards, etc.

I'd take the gram, kilogram, meter, centimeter, etc. over that any day, regardless of how it's calibrated!

It really is fascinating though how much thought 18th and 19th century scientists put in to accurate weights and measures.

Re:Kilogram Scmilogram

[fr2asbury]

Why embarrassed? Does it work for you? If so, what's the problem? As much flack as Americans take around here for using those units, it's important to remember a couple things. Where it really matters, American industries ARE using the metric system. Also, I'm of the opinion that our inches, feet, yards, miles, ounces, pounds and farenheit degrees are more practical for day to day use for the average person.
This is just an example but there is no way to divide metric units of mass or distance in thirds.
The inch is conveniently larger than the centimeter and the foot is just right. You can tell instantly if a person is short if they're less than five feet and tall if they're more than six feet tall. With the exception of very tall people, nearly all adults are 1 meter-something.
With temperature, in celcius less than 10 degrees is fairly chilly but by 30 degrees it's hot. For me it's not hot till it gets over 80F. Celcius degrees being bigger allow for a lower level of subtlety in the weather temperature.
Anyway the metric system is great and has it's places, but don't feel embarrassed that you buy a gallon of milk or a pound of butter.
Oddly enough, in America we've really taken to the 2 liter bottle for our carbonated drinks.

Re:Kilogram Scmilogram

[amliebsch]

I agree that the imperial system is slightly more practical in base units. But it's real utility comes from something unrelated - the fact that it is a largely base-12, not base-10 system. This makes it much simpler to use, because as humans we most often tend to need to divide things by 2, 3, or 4 (or multiples thereof), which base-12 units divide evenly into (and six as a bonus). Icky base-10 units only divide evenly by 2 and 5. Much less useful.

Of course, there's nothing that says the SI system has to be base-10, or that the imperial system must be base-12. But it is, and the imperial system is largely base-12.

Personally, I strongly favor switching all everyday numbering from base-10 to base-12.

Re:Kilogram Scmilogram

[Anonymous Coward]

the fact that it is a largely base-12, not base-10 system

It's far from largely base-12. The imperial system has 12 inches per foot and 12 Troy ounces per pound, but that's only two conversion factors out of the whole system. In general, there's no consistency.

• 12 inches in a foot
• 3 feet in a yard
• 5.5 yards in a rod
• 4 rods in a chain
• 10 chains in a furlong
• 8 furlongs in a mile

Furthermore, having 12 inches in a foot is only convenient if the thing you're dividing is a whole number of feet. If, for example, you're dividing an 8.5-inch wide sheet of paper into columns, it doesn't help at all.

Re:Kilogram Scmilogram

[Anonymous Coward]

Icky base-10 units only divide evenly by 2 and 5. Much less useful.

That's why in the civilized parts of the world we learn (*gasp*) fractions and decimal numbers.

A third of 1m is 333mm, easy as pie.

Re:Kilogram Scmilogram

[vidarh]

Funny. I'm of the exact same opinion about the practicality of metric over imperial. Do you perhaps think it has to do with the fact that we've been immersed by these systems since birth?

As for the silly example of division: I've never come across it as a problem. First of all, I do know how to use fractions. Secondly, approximations are usually good enough, and "everyone" knows that a third is roughly .33 and 2/3's are approximately .67. If you need to state it precisely, you give the fraction: a third of a kilometre, two thirds of a kilo. It's no harder for me to do that than it is for you to divide up your units. Furthermore, I don't have the faintest idea HOW your units relate to eachother. With the SI units you at least only need to learn the prefixes and you can tell any relation between units of the same type.

As for knowing if people are short, that depends entirely on your point of reference again. To me, at 6'2", people around 5'6" are "short" to me, and I don't consider myself tall anymore - I have lots of taller family members and I see taller people around me wherever I go.

As for temperature, I can't feel the difference between temperatures one degree apart, so it really doesn't matter. Though I've always found it more logical to have 0 as a rough measure of the freezing point of water, and 100 as a rough measure of the boiling point of water (both obviously dependant on pressure, but for daily use it hardly matters)

You can try to rationalise it as much as you want, but it all boils down to one thing: You're used to imperial based units, just as I am used to SI units.

The one advantage of the SI system is the uniform naming and conversion ratios, and the fact that they're the same everywhere.

Even the US government recognises those advantages - the US was one of the original signatories to the treaty of the metre, and all imperial based units in use in the US have been defined in terms of the metric units a century or so. It's just a matter of time before metric takes over in the US as well - in particular as government organisations are now required to use metric.

Hmm...

[ProudClod]

Planck's constant would be a very elegant solution - it being the smallest possible quantity of energy, and of course, energy == mass * c^2

Re:Hmm...

[Anonymous Coward]

As my physics teacher would say "Units, units, units!". (Much better than "Developers, developers, developers,...")

Planck's constant has units of Js , so cannot possibly be "the smallest possible quantity of energy"...

Re:Hmm...

[Anonymous Coward]

Planck's constant would be a very elegant solution - it being the smallest possible quantity of energy, and of course, energy == mass * c^2

Replacing the metric system with scaled Planck units would be even better. The rest of the world might not want to go to the effort of changing to a new system, but if Americans have to change from the current system anyway, might as well have units related to the speed of light, the gravitational constant, Planck's constant, and (for electrical units) the charge of the electron.

Re:Hmm...

[ProudClod]

Plank's constant is a single Quanta of energy. If you subscribe to Quantum Theory (and most people do), then energy only comes in blocks of "Planck's Constant" joules, and thus it's the smallest possible quantity of energy.

Re:Hmm...

[rangek]

Planck's constant would be a very elegant solution - it being the smallest possible quantity of energy

Huh? The units of Planck's constant are energy times time (eg., J s).

Re:Hmm...

[Anonymous Coward]

This is irrelavent to Americans.

Re:Hmm...

[MarkRose]

Yes, but how precisely do we know the value of Planck's constant compared to a relatively large volume of water at a specific temperature? Planck's constant would indeed be very elegant, but would it be as accurate?

Re:Hmm...

[ProudClod]

That was the problem that sprung to my mind the first time I read the post - as I misread it as Hubble Constant. Now, the Hubble constant has changed a hell of a lot over the last 100 years, so I was going to moan about inaccuracy.

However, for Planck's constant I'm going to have to defer - I haven't got a clue :)

Re:Hmm...

[ProudClod]

I point you in the direction of the excellent Physics 2000, which is horribly patronising, but informative.
http://www.colorado.edu/physics/2000 /quantumzone/p hotoelectric2.html

They even go on to do a bit of wave/particle duality at the end :)

Js is the unit of impulse, by the way.

Re:Hmm...

[darco]

It is also largely irrelevant to everyone else in the world. The only people that this would affect is scientists who are doing very, very precise measurements--virtually all of whom use the metric system, american or not.

Re:Hmm...

[iamlucky13]

Presumably this method would take into account somehow the actual gravitational force, since it varies pretty significantly depending on where you are?

Re:Hmm...

[Pseudonym]

Plank's constant is a single Quanta of energy.

No. Planck's constant gives the amount of energy carried by (and hence gives a meaning to the momentum of) a photon of a certain frequency. Its units are Joule-seconds, which is not a unit of energy. Since the frequency of a photon can be arbitrarily low, so can its energy.

Re:Hmm...

[slonik]

First of all, Plank constant is a unit of a quantity called "action" and is measured in Energy x Time (like JxS).
Secondly, in high energy physics one is accustomed to so called natural units where velocity is measured as fractions of speed_of_light and Planck's constant value is chosen to be 1 (unit). This gives rise to a nice relations between units of time, length and mass. To cut it short if one can accurately measure time (with some nuclear clock) such measurements can be converted into measurements of mass or/and length.

Re:Hmm...

[Anonymous Coward]

So is the proper spelling of english words :)

Re:Hmm...

[fermion]

The issue is not really manipulating variable to solve for the desired quantity, but rather developing an elegant process to allow a well trained individual to derive the unit independently. What we are trying to do is not have a small group of people copy the artifact, and then make copies of the copy for everyone else to use as a standard. the copying introduces uncertainty. Alllowing everyone to create an original solves that problem.

Secondly, there is really only one quantity that we take as certain: the speed of light in a vacuum. It is defined as a certain exact number. The meter, the second, the Lunin, and to some degree the ampere, are known and reproducible units because they are defined in terms of light, and the process of deriving them is a simple matter of counting collisions. The kelvin is reltively well defined because it using a unique physical quantity.

But the mass, and by extension the mole and really the ampere, is basically a measured by a big hunk of metal, and we hope that hunk is not shedding or gaining atoms. 12/1000 of the mass of that hunk of carbon is a mole.

So, we are not going to convert mass to energy to measure mass. With an AFM we might one day count atoms of a certain substance and know that is a gram. For instance a carbon nanotube with 5018333333333333333333 or a a monolayer of gold with 305685279188... atoms. Of course you would have to purify your sample to make sure all the atoms have the same number of nuetrons. Likewise, we may one day have an STM that move the correct number of atoms onto a substrate.

In siencefiction times, we may one day use a matter/energy translator to convert a certain amount of energy to mass standard. However, you then have that pesky 1 part in 10^-15 uncertainty in planks constant, which means that it is hard to design an experiment that has less uncertainty. Planks constant is among those about which we are the least certain(the gavitational constant is the only one that is really worse).

Re:Hmm...

[tverbeek]

If you subscribe to Quantum Theory (and most people do)

I used to, but stopped once I discovered I could get it on the web for free.

Re:Hmm...

[rangek]

point you in the direction of the excellent Physics 2000, which is horribly patronising, but informative.

"Horribly patronizing" does not even begin to describe that site...

Any way, there is nothing there that says h has anything to do with the smallest amount of energy. It just says photons have E=hv. What stops me from picking v as small as I want?

Re:Hmm...

[ph43drus]

I like it when you define hbar = c = 1 (Plank's Constant over 2*pi, instead of being in energy/Hz, it's in energy*sec/radian). Once you've done this, because of E = mc^2, mass has units of energy, and then time and distance both have units of 1/energy. Neat, eh? It's the natural unit system of the universe. It's pretty inconvenient unless you do particle physics, however.

Basically, the idea is once you've got c, hbar, and the three basic unit types (mass, length, time), you've got a complete system of units. c and hbar then turn into conversion factors which can be set arbitrarily to get a system of units--this is what actually makes the Plank's constant elegant, by nailing it down as an exact number, we've completely defined our system of units (c is already a defined quantity). Then, more accurate measurements of hbar are not measurements, so much as refinements of the definitions of kilograms, seconds and meters.

Jeff

Re:Hmm...

[barawn]

First of all, Plank constant is a unit of a quantity called "action" and is measured in Energy x Time (like JxS).

Or, more typically, a quantity called "angular momentum" (in "momentum * distance", or "kgm/s * m", which works out to be J*s as well). Planck's constant (well, hbar) is the smallest amount of angular momentum, not the smallest amount of energy.

There is, in fact, no 'smallest unit of energy' in current physics. To get that, you'd have to construct the Planck mass, which requires assuming that spacetime itself is quantized.

Re:Hmm...

[barawn]

Basically, the idea is once you've got c, hbar, and the three basic unit types (mass, length, time), you've got a complete system of units.

Nope. You're still missing charge, and possibly something like baryon number or color or something bizarro like that.

For charge you have to measure the charge of the electron, and set it to 1. Then, as you said, more accurate measurements of e are refinements of the definition of a coloumb.

Re:Hmm...

[Anonymous Coward]

Before this you should prove that there is a mass gap in Yang-Mills theory: http://www.claymath.org/millennium/Yang-Mills_Theo ry/ (and in the process earn a million dollars)

Picture of the Kilogram Prototype

[pboyum]

Picture of the International prototype kilogram:

http://www1.bipm.org/utils/common/img/mass/prototy pe.jpg

Re:Picture of the Kilogram Prototype

[cerberus4696]

I feel like I should know this, but why is it in a vacuum jar? Is it to prevent decay?

Re:Picture of the Kilogram Prototype

[SnowZero]

Here is the article linking to the above picture. Anyone know why they chose platinum-iridium?

Re:Picture of the Kilogram Prototype

[spectasaurus]

Better question. Why is it in 3 vacuum jars?

Re:Picture of the Kilogram Prototype

[chiph]

It's to prevent it from collecting dust, which would change the weight.. err, mass. Corrosion prevention might be a goal, too (yes, the alloy is corrosion resistant, but not entirely corrosion proof.) I don't think they're worried about evaporation, though (all substances outgas to a certain degree, some more slowly than others)

It's nested in several jars for redundancy.

Chip H.

Re:Picture of the Kilogram Prototype

[Anonymous Coward]

This is probably a stupid question, but the glass isn't included in the mass of the kilogram, is it?

Re:Picture of the Kilogram Prototype

[MoonChildCY]

Dont miss the followiing FAQ about the kilogram from the same site

http://www1.bipm.org/en/scientific/mass/faqs_mass. html.

Answers all types of questions people asked here, like why they chose that composition, why the shape, etc.

Re:Picture of the Kilogram Prototype

[Anonymous Coward]

Wild guess: decays slowly?

Re:Picture of the Kilogram Prototype

[ink_13]

To keep its mass from changing. You may notice the calipers for handling it in the picture, too. Stray moisture, direct sublimation into the atmosphere, anything that could possibly affect it has to be kept away,

This is the definition of the kilogram. A kilogram is not 1L of H2O at STP (as mentioned elsewhere, pressure depends on mass), it's this little lump of metal. Changes in the mass of it are extraordinarily bad. They make copies of it for reference purposes, and then check the copies agains the original every 10 years. If there's a disagreement, the copy gets adjusted, not the original. The reference lump has actually lost about 50 micrograms in the last 100 years (and no one knows why). That's a lot (well, speaking at the level that micrograms get used at... 1 microgram = 0.000000001 kg), and the really highlights the need for an immutable reference point.

Readers may find the pertinent Wikipedia article interesting.

Re:Picture of the Kilogram Prototype

[Anonymous Coward]

However would'nt a deep vacuum actually increase metal sublimation ?

Re:Picture of the Kilogram Prototype

[ozbird]

To prevent contamination (moisture, hydrocarbons etc.) that may affect its mass. Even so, the Kilogram Prototype has lost some mass (50 micrograms as of 2003) for reasons unknown.

There is an international effort to come up with a new standard extremely precise silicon spheres - the cool thing about them is it is apparently impossible to tell if it is stationary or spinning unless you have a reference point on the surface (e.g. a speck of dust.)

Re:Picture of the Kilogram Prototype

[meringuoid]

The reference lump has actually lost about 50 micrograms in the last 100 years

Just out of interest - how did anyone find out?

Re:Picture of the Kilogram Prototype

[rxmd]

There is an international effort to come up with a new standard extremely precise silicon spheres - the cool thing about them is it is apparently impossible to tell if it is stationary or spinning unless you have a reference point on the surface (e.g. a speck of dust.)

Should be reasonably easy. Just tilt the container. If there's precession, the sphere is spinning.

Re:Picture of the Kilogram Prototype

[Clueless Moron]

The reference lump has actually lost about 50 micrograms in the last 100 years

Is that 50 micrograms of current grams or grams 100 years ago? Ok, small difference I admit...

After all, the thing is still exactly 1kg by definition, so technically it has lost 0 grams.

This sort of thing really underlines why we need a better definition of mass...

Re:Picture of the Kilogram Prototype

[inject_hotmail.com]

Picture of the International prototype kilogram

They are using Russian dolls to demonstrate the new standard? What the!

Perhaps it is a neo-commie plot! Run AWAY!

Inject.
In mother Russia, single kilogram cylinder measures YOU! (sorry, had to)

Re:Picture of the Kilogram Prototype

[Crouchy]

Bellow link suggests that when the kilogram was devised it was based on 1 litre of Pure water. As a side note, when I bake I simply change ml to grams when weighing water (close enough for cooking).

http://www.answers.com/main/ntquery?method=4&dsid= 2040&dekey=kilogram&gwp=8&curtab=2040_1

Re:Picture of the Kilogram Prototype

[jasonjacks0n]

This is the definition of the kilogram. [...] If there's a disagreement, the copy gets adjusted, not the original. The reference lump has actually lost about 50 micrograms in the last 100 years (and no one knows why).

Ok, maybe this is a silly question, but if that's the definition of a Kg, how do they know it's lost mass? Especially if they don't know why?

Are they comparing it to copies of itself, and finding that m of n copies agree with each other, but not the original? Or what exactly?

Re:Anyone Else?

[rollingrock]

The SI unit of mass is the kg, not the gram. So in fact a gram is defined in terms of a kg not vice versa.

Woo-Hoo!

[Anonymous Coward]

Time to redo all the science texts.

Re:Anyone Else?

[Anonymous Coward]

No, it's just you (that's the stupid one).

Re:Anyone Else?

[wmspringer]

Which surprised me, too, when I first learned it.. Is that just because the kilogram finds more use?

Pressure

[XanC]

That would work fine, and I believe was the original definition. Unfortunately, pressure has a mass component, so your definition is circular.

Re:Pressure

[thedustbustr]

Could you please explain why that matters?

Re:Pressure

[XanC]

Unfortunately, pressure has a mass component, so your definition is circular.

Could you please explain why that matters?

Recursive (adj): See recursive

Re:Pressure

[rgmoore]

So define it as a different volume of liquid water at water's triple point. The triple point specifies a temperature and pressure based on the physical properties of water, which eliminates your objection. The Kelvin temperature scale is already defined using the triple point of water, so there shouldn't be any problem using it in another basic definition. A more practical problem is that we simply don't have the technology to build a container whose volume is as precise as we'd like the standard for the kilogram to be.

Re:Pressure

[Anonymous Coward]

If you say that 1kg is 1 liter of water at STP then how do you define pressure? Right now STP is 0C and 101325 Pa. But a pascal is 1 kg/m*s^2, and if you don't have kilogram defined then that would be a pretty meaningless definition.

Re:Pressure

[XanC]

You could do that, but then you've got pressure as one of the fundamental units, and kilograms defined in terms of that. (Quite disruptive.) And then you would have the same trouble defining pressure that we're having defining mass.

Re:Pressure

[dspeyer]

Doesn't strike me as much trouble.

If the pressure which causes the triple point of water were appled to a square meter, a kilogram will be accelerated at x meters/seconds^2 where x is something we can measure very accurately. We can use this to define a kilogram. Admittedly, it's a little convoluted, but I suspect we can do the measurements much better than we can for Planks constant or Avagadro's number. There's also a smaller risk of discovering some twist in physical law that makes what we've done ill-defined.

Some what would this disrupt?

Re:Pressure

[logicnazi]

Yes, you are clearly right that we could define mass in terms of 1 litre of water at its triple point (though ATP wouldn't work well). The question simply comes down to the question of whether this will be as useful and give us as accurate results.

First of all I don't think this would be as useful a definition. One of the benefits of fixing things like Avagadro's constant of Plank's constant is that they allow us to eliminate sources of error in other important physical measurements. I simply don't think we have any important measurements about water or pressure which need anywhere near as much precision as quantum measurements which rely on plank's constant or the mass of an atom (which is fixed by fixing av's constant).

The second issue is whether this definition which have the desired accuracy. Quite frankly I think it will be *very* difficult to measure 1 liter of water at its triple point. For instance where exactly is its triple point, how can you be sure you aren't .01 degrees above the triple point? I suspect that while we can measure length quite accurately between free floating objects measuring the volume in some kind of container would be very difficult. In particular getting an accurate volume measurement would require creating a perfect geometric box and even the slightest imperfections in the containers walls would deystroy the volume measurement.

Besides, in general I doubt if the statistical behavior of molecules as guaranteed by thermodynamics is exact enough to serve future needs. Ultimately where the triple point of water happens is a statistically property of many atoms and it probably doesn't happen at a perfectly sharp point but over some vague range. The definition of the other two quantities alows much greater preciscion.

Re:Pressure

[logicnazi]

No, he doesn't. The triple point is a purely observational phenomenon (do all three states coexist) and does not rely on a definition of pressure.

I still don't think it is a good definition and I posted a long reply to this effect.

Re:Pressure

[XanC]

I stand corrected! You don't need to know anything about pressure to measure volume at the triple point.

It's still not a good way to go about it, as you say in your other post, but not for the reason I was stating.

Re:Pressure

[fbform]

You could do that, but then you've got pressure as one of the fundamental units, and kilograms defined in terms of that.

Why? As your parent noted, the current definition for Kelvin is "1/273.16 of the absolute temperature at the triple point of water", and that does not run into any difficulty with pressure. We could redefine the kilogram to be "the mass of X cubic meters of water at its triple point". Measuring the pressure is irrelevant - just tweak the temperature and pressure until you see all three phases coexist, and measure out X cubic meters of that and call its mass "one kilogram".

I would however prefer a name other than the "kilogram" - it's very embarassing to have a "kilo" prefix in a base unit.

Re:Anyone Else?

[Tomfrh]

Defining the kilogram DOES define the gram.

Obligatory Simpsons Metric Quote

[shiafu]

Lisa: Principal Skinner, how's your transportation project coming?

Skinner: Not only are the trains now running on time, they're running on metric time! Remember this time people, 80 past 2 on April 47th. It's the dawn of a new enlightenment!

Re:Obligatory Simpsons Metric Quote

[Anonymous Coward]

"The metric system is the tool of the devil! My car gets forty rods to the hogshead and that's the way I likes it."

-- Abe Simpson

Re:Obligatory Simpsons Metric Quote

[tehshen]

My friend and I tried to use metric time once. It is a lot harder than it looks (7.50 o'clock news anyone? Church mass at 3.75?) Metric time is useless if not enough numbers divide into ten.
Attempts of a JavaScript clock are here if anyone is interested.

Re:Obligatory Simpsons Metric Quote

[Angstroem]

So why is it the seconds are leaving out certain numbers? The last time I checked, the metric system didn't have any holes in it.

Re:Obligatory Simpsons Metric Quote

[tehshen]

I made the day equal in both systems, as I can't change how long the Earth takes to rotate. There are 100000 metric seconds compared to 86400 usual seconds, so the metric seconds are slightly shorter (more in a day). The missing seconds are there, just not being shown due to the limitations of JavaScript.

Re:Obligatory Simpsons Metric Quote

[amliebsch]

"metric" != "base-10"

hmm not really math is this?

[qleak]

I'm not sure how this slipped by in slashdot but this has nothing to do with the academic area of mathematics :-P Sounds a lot more like science or physics to be specific. C'mon people lets try to give things a realistic category. Anyway why the hell is math a subcategory of science?? Just my 2 kilos, flame me if you like.

"or the mass of a fixed number of atoms"

[physicsphairy]

Well, count the number of atoms in the platinum-iridium alloy, and voila! You have your new definition! (without having to fuss with the traditionalists)

Why the motivation for the change? The mass of subatomic particles have been given in kg for over a century. What exactly needs a more precisely reference of measurement? Physicists use their own units when it's convenient anyway. . . .

Re:"or the mass of a fixed number of atoms"

[geekyMD]

count the number of atoms in the platinum-iridium alloy

And how do you propose we do that? That's exactly why the article was talking about using x-ray crystallography, but you just can't do that on a 1kg block of iridium-platinum alloy.

Why the motivation for the change? The mass of subatomic particles have been given in kg for over a century. What exactly needs a more precisely reference of measurement? Physicists use their own units when it's convenient anyway. . . .

Lets say someone disputes the mass of a kilogram at the 10^-8 digit: In order to verify this cylinder has to be re-weighed. Not only is this inconvenient, but if someone has polished it or even 1 pg of dust has fallen on it, the precise weight is no longer repeatable, and is a ludicrous basis for measuring the mass of subatomic particles.

But more importantly, there are many standard units in SI that have an uncertainty of 0, the speed of light, and the second among them. The kilogram however, has non-zero uncertainty, which keeps us from refining other measurements that are based on the kilogram. So if we can measure the kilogram exactly, based of a physical constant in the universe and not a block of fickle matter, then we can measure other units either exactly or with higher precision.

The whole point is that the kilogram is not defined precisely enough, and its current referent is variable, which makes other measurements variable and imprecise.

Re:"or the mass of a fixed number of atoms"

[BigusDickus]

Okay, but what do you do about the isotope forms of platinum and iridium? Different atomic weights. If would only work if you could get them only in mono-isotopic form.

Re:"or the mass of a fixed number of atoms"

[physicsphairy]

And how do you propose we do that? That's exactly why the article was talking about using x-ray crystallography, but you just can't do that on a 1kg block of iridium-platinum alloy.

Why use its known mass, of course! Then divide by 0.198078 (if it were pure platinum)/6.022E23 and take the nearest integer.

It doesn't really matter that there might plausibly be more or less atoms. Just find a number, suitably truncate it, and declare all subsequent decimal places to be zeros.

Isn't this exactly what happened with regards to the meter? "Hmm... speed of light is about 299,792,458 meters per second... well, instead of measuring this funky rod anymore, let's just say that it's 1 second of light movement long."

I'm proposing we do the same thing with this block that we did with the rod.

Lets say someone disputes the mass of a kilogram at the 10^-8 digit:

I presume you mean decimal place. Well, that's easy. A kilogram weighs 1.00000000kg. There you go, 1kg to the eight decimal place.

Not only is this inconvenient, but if someone has polished it or even 1 pg of dust has fallen on it, the precise weight is no longer repeatable, and is a ludicrous basis for measuring the mass of subatomic particles.

That's just silly. We've never weighed out the block to the precision of picograms. Yet, somehow we still relate measurements on the picogram scale, don't we? The weight of the actual block is only definite to about 2 micrograms.

All that's really important is to have a defined conversion from whatever more useful units you're using.

In the same way, I can give you an accurate description of the length of a cesium nucleus in furlongs. Furlongs, obviously, were not in their origination a very precise unit of length at all. But since there is a standard conversion (1 furlong = 201.168 meters) any measurement I give you in furlongs is as good as a measurement given in meters--as long as we agree on the conversion factor.

Here's the crux of it all: pretty much all measurements of particle mass are computed in energy (electric volts), chemistry is done in atomic mass units, and there are various other specialized units that are always cropping up. When you see a particle mass or some such given in kg, it is infallibly a conversion from these other units. As long as we agree on the conversion factor we are going to use between kg and some mass unit dependent on c, it is as good as defining kg on c in the first place.

I might go so far as to say that, even if we don't agree, it doesn't particularly matter. Honestly, the only reason we ever give the mass of an electron in kilos is because Joe Schmoe wants to know how much an electron weighs compared with how much he weighs.

Re:"or the mass of a fixed number of atoms"

[jerde]

You're missing the important point here: We need a definition that others can reliably reproduce, to whatever precision they need.

It's not about just writing down a number and truncating it... it's being able to arrive at that number TO THAT PRECISION again in the future.

>It doesn't really matter that there might plausibly be more or less atoms.

YES IT DOES! If you're _defining_ something to be a certain number of atoms, you'd better be pretty damn sure it's the right number of atoms.

We didn't just fudge the definition of the meter: it's now defined in such a way that you can get yourself a meter of however much precision your equipment is capable of, and ANYBODY can recreate that equipment and come up with the same meter. It's based on physical constants in such a way that it doesn't matter what physical objects you use to measure it.

(Well, you have to have some Cesium and some photons. With those two, and any equipment to measure some their properties, you get the second and the meter.)

>All that's really important is to have a defined conversion from whatever more useful units you're using.

You can have a defined conversion specified to a hundred decimal places, if you want... but it's useless if the unit you're comparing it to can only be measured accurately to 6 places. (and has the possibility of CHANGING because it could gain or lose mass, being a physical artifact)

There is NO limit to the precision we can measure time or distance in, now, except the fundamental limits of the universe itself. (quantum effects) We need the ability to do that with mass, now, too.

- Peter

May I be the first to ask...

[Murphy Murph]

Could someone please explain to me "a quantity of light" having mass?
I am honestly confused. (and ignorant)

Re:May I be the first to ask...

[Anonymous Coward]

How do you think solar arrays work then? The particles have a small enough mass to make electrons move when they strike the shells of other atoms.

Quite elementary really. We learned this in third grade.

Re:May I be the first to ask...

[ProudClod]

The elementary particle of light, or photon, has energy of hf - that is, planck's constant multiplied by the frequency of the light. As we can use Einstein's equation E=mc^2 to link energy and mass, thus a quantity of light has mass.

I'll attempt to derive an equation for m now, it's probably wrong - I'm not a grand physicist, and I'm very tired:

E=hf
v=f(lambda)
E=mc^2

thus mc^2=h(v/(lambda))
the v and c cancel (as the velocity of light is c)
mc= h/(lambda)
m=h/(lambda)c

Re:May I be the first to ask...

[celeritas_2]

while photons are by definition massless, each one represents an exact amount of energy. Einstein gave us e=mc^2 (energy and mass are the same thing) so a photon sort of has mass

Re:May I be the first to ask...

[Thingummywut]

Light does NOT have mass. Photons have momentum but not mass. And since they don't have mass, they're traveling at exactly the speed of light.

Re:May I be the first to ask...

[CRepetski]

No quantity of light has mass. Period.

Light consists of photons, which are massless. They do have energy (E=momentum * speed of light = Planck's constant * frequency) and momentum (p = planck's constant / wavelength).

Perhaps some people in this subthread are getting confused with the DeBroglie wavelengths, which is a property all particles, having mass or otherwise. The DeBroglie wavelength is equal to Planck's constant / momentum, so for a photon this is the same as its actual wavelength.

Re:May I be the first to ask...

[CRepetski]

Sorry to respond to my own post.

E = m*c^2 refers to the amount of energy contained in the rest mass of a particle. This is applicable for particles of mass, such as electrons, protons, etc. It is NOT a valid formula in the case of photons, since photons travel at the speed of light, they have no rest mass.

Note, E = m*c^2 isn't the formula for the entire energy of a particle, only for its rest energy. To find the total energy you need to multiply m*c^2 by gamma, where gamma = (1 - v^2 / c^2)^(-1/2). If you expand this you see that for non-relativistic particles the kinetic energy formula E=m*v^2/2 is a pretty good approximation.

Re:May I be the first to ask...

[DavidTC]

To clarify, all particles have mass, and this mass turns into energy as they go faster, turning completely to energy at the speed of light. Mass is measured at 'rest'. (That is, in the same frame of reference as the particle.)

Since photons, by defination, cannot go slower than the speed of light, the amount of mass they have is the amount of mass they would have if stopped. Or, to put it another way, it's the amount of mass they would have if you could measure their mass while traveling at the speed of light.

Which is why it's called 'virtual mass', as you can't actually do either of those. All you can do is calculate the mass from the energy of the photon. (Which, as another post pointed out, is set by the frequency.)

Re:May I be the first to ask...

[ltbarcly]

I'm sorry, but this is just false.

A thing has mass. The thing is measured in a frame that is at rest relative to it. Now you measure it in a frame moving quickly relative to the thing. The thing weighs more because the energy of the movement is equivelent to mass by E=mc^2. Thus when something moves it weighs more, and the faster it moves the more it weighs.

You can figure out the weight by using an equation (I don't remember exactly, it may have constants) like m/(1-V^2/C^2). Where V is the velocity and m is the rest mass. As you can see, when V = C, the equation is m/0. That is why you say that something has infinite mass when it is moving at the speed of light.

Now, photons have mass because they are a form of energy. Since energy and mass are the same thing, you just figure out how much energy a quanta of light has at some frequency, and convert it to mass using E=mc^2, or rather m=E/c^2.

There is no such thing as 'virtual mass' as you speak of it.

Finally, photons cannot go slower than the speed of light as a result of special relativity. This is not by definition, but rather it is an astounding fact, that regardless of reference frame c remains constant.

Re:May I be the first to ask...

[Milhouse_ph]

I don't think you've quite nailed it either.

Objects that travel at the speed of light have no rest mass. And therefore no "real" mass to speak of. Using the E=mc^2 and using algebra to derive the mass is not really the correct way to do things. See this post and it's reply which has a bit more info. Now if you want the truth I don't know much about the Higgs mechanism which is theorized to be what actually gives rise to mass, but AFAIK mass and energy aren't the same thing. You can turn one into the other and vice versa, pair production or particle/anti-particle reactions, but they have to be converted first by these reactions.

This seems to be a good overview of a photon's mass and why it needs to be zero for certain phenomenon to exist (such as gauge invariance and inverse square law):

http://math.ucr.edu/home/baez/physics/ParticleAndN uclear/photon_mass.html

Re:May I be the first to ask...

[Pseudonym]

The elementary particle of light, or photon, has energy of hf - that is, planck's constant multiplied by the frequency of the light. As we can use Einstein's equation E=mc^2 to link energy and mass, thus a quantity of light has mass.

The famous equation should be more correctly written E = m_0 c^2, where m_0 is the rest mass. A photon is never at rest, and hence has no rest mass.

The relativistic equation for the kinetic energy of an object is E^2 = m^2 c^4 + p^2 c^2. Since a photon has zero mass, all of its kinetic energy is in its momentum.

Re:May I be the first to ask...

[Anonymous Coward]

Don't you feel like an idiot getting it so wrong?

Re:Anyone Else?

[Otter]

Explanation...

In summary, the kilogram is the basic metric unit of weight, not the gram. The gram will be defined by the kg standard.

How is the US pound measured?

[Anonymous Coward]

If the Kilogram is measured by a cylindrical object, how is the Pound accuratly measured? Is it a mesurement of force, or a natural scale, object?

Re:How is the US pound measured?

[XanC]

The pound (mass) is defined as a certain number of kilograms. Just like the inch is defined as a certain number of centimeters.

Re:How is the US pound measured?

[AtillaTheKilla]

Pounds measure weight, my friend. As in the effect of a gravitational field on a certain mass.

Re:How is the US pound measured?

[XanC]

From Wikipedia:

The pound (avoirdupois) or international pound, abbreviation "lb" or sometimes # in the United States, is the mass unit defined as exactly 0.45359237 kilograms

When a pound is called a "unit of weight", it is often the unit of mass.

But pounds are also used for the force definitions of weight, in which the pound force is a unit of force equal to 4.448 newtons. That is the force due to gravity of a pound (avoirdupois) where the acceleration of gravity is 32.17405 ft/s2

Re:How is the US pound measured?

[takeya]

I believe it's the other way around. A kilogram is 2.20462262 pounds, and 1cm is 0.393700787 in.

I'm joking of course, but seriously imperial measurements have been around longer than the metric system.

Re:How is the US pound measured?

[spaceyhackerlady]

Pounds measure weight, my friend. As in the effect of a gravitational field on a certain mass.

Those who use pounds as force use slugs as the unit of mass. Same relationship as mass in kilograms and weight in newtons (i.e. Newton's 2nd Law), except for the weird-ass numbers.

Just how many hogsheads are there in a fortnight, anyway?

...laura

Density

[XanC]

Originally, yes. But the density of water varies based on temperature and pressure, so that really doesn't work for any kind of precision.

The pressure part really kills using water as a definition, because it has a mass component. Circular definitions are a no-no.

Bah

[jlechem]

"My car gets forty rods to the hogshead, and that's the way I likes it!"

A little offtopic but still revelant ;-)

Re:Bah

[Tomfrh]

I was waiting for that one!

Re:Bah

[the eric conspiracy]

That's pretty crappy gas roddage.

I get at least 450,000 rods per hogshead highway.

Re:Bah

[Anonymous Coward]

"-This car can go forty hectares on a single tank of kerosene!
-What country is this car from?
-Well, it no longer exists"

Re:Bah

[rob_squared]

"My car gets forty rods to the hogshead, and that's the way I likes it!"

These are actual units of measurement:

40 rods = 1 furlong (fur) = 660 feet

Re:Bah

[johnw]

Given the tendency to measure fuel consumption in litres/100k, I can cancel down and say that my car's fuel consumption is about 0.05 square millimetres.

If you prefer the imperial measure of miles/gallon, you could similarly reduce it to inverse acres.

John

That'll really help...

[teutonic_leech]

... adoption of the metric system over here in the U.S. - LOL. For the unitiated: the metric system was supposed to become the 'standard' in the U.S., but as usual, everyone's been dragging their feet. I think it's a good idea theoretically, but in the rest of the world it would require to replace all scales in circulation. Actually, come to think of it, since the metric system is rarely used over here in the U.S., it might actually make sense to make that change (whichever standard will be adopted) and start pushing it on the American continent. Since there's not much of a pre-existing 'metric' infrastructure, it should be easy to introduce a modded kilogram.

Re:That'll really help...

[XanC]

The "standard" in the US really is the metric system. All the units that people actually used are defined in terms of their metric counterparts.

So a change in the kilogram automatically affects the pound.

However, when they do make this change, it will not be a "modded" kilogram. It will be the same mass as before; it's just that it will be possible (ultimately) to measure it much more precisly and time-invariantly (as the standard is losing mass over time).

Re:That'll really help...

[jsoderba]

Whatever measure might be selected to replace the standard weight, it will certainly be chosen to be as close to the mass of the current kg as humanly possible.

Re:That'll really help...

[Anonymous Coward]

> it might actually make sense to make that change [...] and start pushing it on the American continent

The American continent is already using the metric system since quite a while, just like the rest of the world. Only a part of northern America doesn't. But why would they, when they have the backing of countries like Burma and Liberia -- the only other countries measuring in lengths of body parts. :-]

Re:That'll really help...

[Anonymous Coward]

Err... it's probably far too late to mass-force an introduction of the metric system into the US. It will have to be very gradual.

I mean, can you imagine how many trillions of dollars are invested in infrastructure, tools, and equipment that use the old imperial system? Stuff like that doesn't just get replaced (and work!) overnight.

Re:That'll really help...

[CRepetski]

For the unitiated: the metric system was supposed to become the 'standard' in the U.S., but as usual, everyone's been dragging their feet.

Hah! Dragging their feet! Get it?

Re:That'll really help...

[Anonymous Coward]

The American continent?

Thanks, but us residents of the Soviet Republic of Canuckistan are already quite happy with our metric system

Re:That'll really help...

[Random Hacker]

Actually, the metric system is in wide use here in the U.S., to the point where the continued use of the imperial system is annoying. The only sockets, allen wrenches, etc. I need for my bicycle or my car are metric. But carpentry is still stuck in those English units that not even the English use anymore.

Also, any redefinition of the kilogram will have no practical effect on everyday measurements, as the difference will be in the parts per million. Nobody except a few metrologists will have to buy a new set of scales.

mnb Re:Pressure

[Anonymous Coward]

Ahh - good point.
Make's me feel stupid, but good point.

(I'm not the grandparent poster - but I thought the same thing.)

Finally...

[Jon Abbott]

I can rest at night, not thinking about plum-sized cylinders of platinum-iridium alloy.

because....

[spdt]

..it has been a "block of metal" for some time, and now we're realising that we need for it to be a universal constant. It's actually being changed, which is the news.

Good idea.

[jnkt]

The idea is sound I think. If we ever hope to get the back waters of society ( US, UK? ;-) to tag along with a common set of units, then we should try to fix the last outstanding defects of our own system first. Sure, it will be expensive as hell, but what is the current yearly cost of having two competing measurement systems today? Would be interesting if some one had some figures to do a quick ROI. The result might show if this is just another insane idea, or actually economically feasable.

Re:Good idea.

[fr2asbury]

Well seeing as how the imperial system is really only used inside the US for the US consumer and all our industry uses metric internally, I suspect the cost of maintaining two systems that don't really compete is fairly low.

Re:Good idea.

[jnkt]

Last I checked, most applications or libraries which have to deal with units implement support for both the metric as well as imperial. For ex. Last week, I had to do some stuff with the JText library and the first step was to implement a conversion utility from and to metricimperical, since the library was written by americans, only supporting imperical units.

Imperial measurements are certainly not only affecting american users, as well as SI/metric units are not only affecting "ROW"-users so my question still remains.

Nope, sorry

[mrchaotica]

You'd lose mass instead.

Re:Nope, sorry

[MagicDude]

Presuming that he's never going to leave the surface of the earth, the two can be pretty much interchangable, hence the commonplace conversion of 2.2 pounds to a kilogram.

Re:Nope, sorry

[Canadian_Daemon]

Except that weight is measured in Newtons (kg*m/s^2).

Re:Nope, sorry

[damiam]

Since Newtons are based on kilograms, any change in the kilogram would also impact weight.

Re:Nope, sorry

[MagicDude]

What I'm getting at is since weight is always going to be a directly proportional to mass by the same constant through his entire life, it's fair enough to say that losing mass = losing weight and vice versa in a vernacular sense.

Re:Nope, sorry

[Anonymous Coward]

But then the mass=weight person grows up to be a space probe scientist and misses a Mars shot because he confuses mass and weight.

Re:Nope, sorry

[Anonymous Coward]

With less mass, and the same gravity, you will in fact loose weight. F=ma.

Re:Nope, sorry

[izomiac]

Well, what if he lives on the top of a very tall mountain and wants to know his weight/mass to several decimal places?

Re:Nope, sorry

[Anonymous Coward]

Isn't that acceleration?

Re:Nope, sorry

[dnoyeb]

instead? Can one loose mass without loosing weight?

Re:Nope, sorry

[ockegheim]

Yes, if the unit of measurement becomes slightly larger, your mass (as measured in kilograms) will decrease.

Re:Nope, sorry

[Anonymous Coward]

But then the mass=weight person grows up to be a space probe scientist and misses a Mars shot because he confuses mass and weight.

But before that, hopefully he will miss his graduate school oral exam and flunk out of school---seriously, anyone with enough of a brain to be in physical sciences shouldn't confuse mass with weight (or centrifugal force with centripedal force).

I'm in favour, the kg doesn't work for me

[confused philosopher]

Being Canadian, I still use pounds to describe my weight as a human being, and a kilogram just doesn't do it for me. I'd be happier if they made it a number that more closely represents the American pound.

But I think what they should do is simply find some natural occurance, that defines the current weight, and so even though the basis of the system would change, the product packagings, and my kg weight on earth wouldn't be changed.

Re:I'm in favour, the kg doesn't work for me

[stevejobsjr]

That's how they do it. The fundamental units have been redefined several times, but to those who aren't scientists, the changes go unnoticed.

Re:I'm in favour, the kg doesn't work for me

[Anonymous Coward]

...then you're not a girl looking for a rapid weight loss... I lost 50% of my weight when I started to use kG instead for pounds... ;-)
70 kG sounds a lot less than 140 pounds...

Re:I'm in favour, the kg doesn't work for me

[nuggz]

Interesting, 70kg sounds like quite a bit more than 140 pounds to me.

(70kg is about 154lbs)

Rather 1kg of C2H5OH ...

[Anonymous Coward]

Yeah, I would rather use C2H5OH ...

Re:Rather 1kg of C2H5OH ...

[Necr0maN]

I believe it's mostly used to define amounts of C17H21NO4 or 3beta-hydroxy-1alphaH, 5alphaH-tropane-2beta-carboxylic acid methyl ester benzoate, also known as your everyday cocaine.

Re:Rather 1kg of C2H5OH ...

[Necr0maN]

and since it has a molecular mass of 303.36u you need about 1985791266331147374307356 molecules of that to get to 1 kg

Re:Anyone Else?

[Anonymous Coward]

Or is this just typical /. editor stupidity?

I was going to be nice to you up until this sentence - if you want to suggest that someone is stupid, can you at least be sure that you're not wrong? Many posts have replied with the appropriate info (not to mention that you *did* pass grade school, did you not - if so, how can you *not* know that the gram is defined in terms of the kilogram?)

In any case, is this just typical Wes Janson stupidity?

Note to self.........

[CSMastermind]

Steal the artifact they use to measure the kilogram right now. That way they'll have to change!!!!

Re:Not really...

[Tomfrh]

There is no precise definition for a litre of water.

1L of water == 1kg?

[ZeroExistenZ]

Even though the kilogram cylinder is housed in a special vault under controlled conditions at the BIPM, its mass can drift slightly over the years and it is subject to changes in mass because of contamination, material loss from surface cleaning, or other effects.

I always thought, that the mass of 1 Liter of water could fill a cube of 1dm, being 1kg. Or am I wrong with assuming that?

Or rather, would changing the globally agreed "Kilo" change as well what we consider as a "Liter"?

Re:1L of water == 1kg?

[emurphy42]

From the Wikipedia article on "kilogram":

The kilogram was originally defined as the mass of one litre of pure water at a temperature of 4 degrees Celsius and standard atmospheric pressure. This definition was hard to realize accurately, partially because the density of water depends ever-so-slightly on the pressure, and pressure units include mass as a factor, introducing a circular dependency in the definition of the kilogram.

Re:1L of water == 1kg?

[Anonymous Coward]

Yes, you're totally wrong. I guess a result of the US-educational system. :(

Re:1L of water == 1kg?

[Teancum]

In addition to the pressure and temperature requirements that are very difficult to maintain, one other huge issue that revolves around water is isotopic purity. The definition says nothing about the makeup of the water, the purity of the water (it might as well be seawater as far as the definition is concerned).

Even assuming super distilled water (it has gone through a distillation process multiple times to reduce mineral content to a near minimum possible with current technology), you still have variations in weight based on the elemental composition of the water itself. If the hydrogen in the water is made up of deuterium or tritium, or the oxygen is something other than the standard O-16, you will begin to have some variations in the density of the water, and an imprecise definition. BTW, water that is made up of heavier isotopes than simple hydrogen and ordinary stable O-16 is called "heavy water", and for a reason.... the water is measureably heavier than ordinary water, even though chemically it is totally identical in composition.

So do you define a kilogram as a liter of heavy water?

Just a block of metal?!

[bildungsroman_yorick]

ITS NOT JUST A BLOCK OF METAL! It represents everything to us metric scientists!

Come with us quietly, Slashdotters. Don't argue or make a scene. Because if you say anything more about changing kilograms or debunking metric systems, we're gonna be forced to take you to a mental hospital. You don't want that, do you?

Gram is dead, Hail Kilo!

Speed of light changes

[alw53]

What happens when the speed of light changes?.

Re:Speed of light changes

[corblix]

What happens when the speed of light changes?

The meter is already defined in terms of the speed of light (the distance light travels in the vacuum in a certain number of seconds), so your question comes a little late.

The real question is how they express changes in the speed of light, now that it has been fixed in terms of meters per second.

Re:Speed of light changes

[rob_squared]

" What happens when the speed of light changes?" "...as recently as 2 billion years ago."

Ahh, the good old days. What are you, frigging nuts?

Re:Speed of light changes

[alw53]

See this for some more contemporary measurements.

Re:Anyone Else?

[Steinar]

The definition is a kilogram because the abovementioned lump of metal is one kilogram. A redefinition may ofcourse change this.

Re:Not really...

[rcamans]

one litre at a specific temperature.
In case you were not aware of it, the density of water varies with temperature. A lot.
Especially at 32 F and 212 F, but plenty in between.

Interest without knowledge?

[Eunuch]

So this is what happens when you have a group of people with such interest in science but little knowledge? When asked to explain why Spears married and divorced that guy so quick, nobody here knows--yet nobody would comment? Yet when asked to explain why we need a new kilogram standard, we get lots of crap and jokes. Just pick up watching sports.

Meh ... how 'bout

[hot_Karls_bad_cavern]

Meh, how about changing the size of a pint!? Huh? Yeah, who's with me on this one? i could certainly go for pints being larger ... 'specially around lunch time :)

Re:Meh ... how 'bout

[Anonymous Coward]

Just don't go to the US -- their pints are 20% smaller. Though when you're drinking American "beer", that's not such a bad thing.

Re:Meh ... how 'bout

[Anonymous Coward]

hur hur hur

Re:Meh ... how 'bout

[vidarh]

You could always change to metric, and insist on rounding up to the closest SI base unit. A pint is 0.568 litres, so that would give you a nice increase.

Each Time?

[OverflowingBitBucket]

So, do we change the definition each time we get a slightly more accurate measure of true weight of some unobservable entity (atom)? Or perhaps keep the definition the same, but just adjust the specification of weight of said entities when we discover new information, rather than saying, oh crap, let's change the definition again? Or worse, let's declare the weight of everything to be invalid and start afresh each time?

I can't believe it

[Anonymous Coward]

I really and honestly cannot believe that all of you morons would argue over the dumbest shit.

You people are in dire need of a life.

They told me that morons hang out here and I just had to see it for myself.

Re:I can't believe it

[BigusDickus]

"You people are in dire need of a life."

Or someplace to go on a Saturday night.

What happens? I'll tell you what happens...

[bildungsroman_yorick]

Fire and brimstone coming down from the skies. Rivers and seas boilin. Forty years of darkness. Earthquakes, volcanoes. The dead rising from the grave. Human sacrifice, dogs and cats living together - mass hysteria.

Still Kg?

[ShadowFlair]

As opposed to what people seem to be suggesting, I don't think they are trying to replace kilogram with a brand-new unit, but just changing the definition. You would still say the brick is 1Kg; however, that will no longer mean that your brick is equivalent to the platinum-iridium cylinder, but a constant as defined by a unchanging natural phenomenon as suggested by the scientists...

Re:Still Kg?

[Dausha]

But, first thing you do is change the definition to something easier to manipulate. Then, over time, you slowly change that value until you arrive at a new one.

Happened when the US went off the Gold Standard.

Re:Still Kg?

[vidarh]

Are you saying that a physical artifact is harder to manipulate than a well defined value? If someone started shaving or adding stuff to the international kilogram artifact it would be easy to afterwards claim that it wasn't the kilogram artifact that changed, but whatever it was compared to. If a kilogram is defined to be a value that is independently measurable by anyone with the appropriate tools that possibility goes away. And this is important because today the kilogram DOES change

Am I Missing Something...?

[Anonymous Coward]

1 gram: the weight of 1 cubic cetimeter of water at 3.98 degrees Celsius.
1 centimeter: distance light travels in 1 / 299 792 458 000 second

1 kg: 1000 grams
The kilogram is already defined purely in terms of natural phenomeon.

Re:Am I Missing Something...?

[emurphy42]

(copy of a reply given to a similar question)

From the Wikipedia article on "kilogram":

The kilogram was originally defined as the mass of one litre of pure water at a temperature of 4 degrees Celsius and standard atmospheric pressure. This definition was hard to realize accurately, partially because the density of water depends ever-so-slightly on the pressure, and pressure units include mass as a factor, introducing a circular dependency in the definition of the kilogram.

Do we actually know atoms have fixed mass?

[Anonymous Coward]

Just wondering... They're saying that we could replace the kilogram with "the mass of a fixed number of atoms". Does every atom have the same mass? How do we know this?

Dupe

[Tab is on Slashdot]

This is a dupe!

What?

[Noose For A Neck]

There is no mass component in pressure. It is force over area - no mass involved.

Re:What?

[TuballoyThunder]

F = m a
(N = kg m s^-2)

Re:What?

[Anonymous Coward]

Force = mass x acceleration. Pressure units are Pascals (kg/(m*s^2))

Obligatory Grandpa quote...

[MagicDude]

My car gets forty rods to the hogshead, and thats the way I likes it!!

I suppose a more appropriate quote would be:

"My car weights 175 stones, and that's the way I likes it!"

Re:Obligatory Grandpa quote...

[Anonymous Coward]

maybe a kilo should be a hogs head of water. That way we can all like it ( except the hog )

Messing up the drug cartel...

[__aaclcg7560]

This is going to have serious implications for the drug cartel. If the drug lords can't agree on what a kilo means for powder, and someone feels shorted, things are going to get really ulgy really fast. The world-wide economy will collapse for the want of a redefined measurement.

Or, in other words, some people just don't know how to leave something good alone.

Force

[XanC]

Force is nothing but mass * distance / time^2. 1 Newton = 1 kg*m/s^2

Re:You mean 6 right? 3! = 3x2 = 6

[Anonymous Coward]

You can distinguish a factorial operator from an exclamation mark by carefully looking for a period at the end of the sentence.

Pi is exactly equal to 3!
vs
Pi is exactly equal to 3!.

Re:Not really...

[Anonymous Coward]

Silly, it is exactly 0.2642 gallons. If you perfer the old Russian system (as I do), a liter is 1.626 vodkabottle (a practical people, the Russians).

Think you mean Planck Mass,,,,

[Anonymous Coward]

...where Planck Mass = sqrt (h-bar*c/G) = 2.176 x 10^-8 kg

Or, 1kg = approx 45.95 million Planck masses

Source: http://en.wikipedia.org/wiki/Planck_mass

Too Vague

[Anonymous Coward]

The current defintion "a cylinder of platinum-iridium alloy about the size of a plum" is too vague.

Re:Anyone Else?

[Anonymous Coward]

defining the kilogram would just be taking the gram and multiplying by one thousand.

Yeah, unless you're weighing something digitally, then you would multiply by 1024.

Mod parent up

[Anonymous Coward]

mod parent up insightful

Re:Mod Parent Up

[Anonymous Coward]

Arthur C. Clarke.

Re:Mod Parent Up

[Gabrill]

Thanks.

Re:Mod Parent Up

[thePjunisher]

Any technology distinguishable from magic is insufficiently advanced.

Re:Mod Parent Up

[arose]

Now we only how to find some magic to compare to...

Re:Mod Parent Up

[vidarlo]

Someone smart famous once said "Any technology, sufficiently advanced, is indistinguishable from magic."

Said by Arthur C. Clarke

My thoughts

[Raul654]

This actually came up in my high school physics class a few years back. Since then, I've given it some thought, and my best guess was to define a kilogram in terms of the deflection of a beam of light under the influence of gravity over a given distance. In other words, define it in terms of the deflect of a beam of light passing a kilogram point charge at a certain distance.

Re:My thoughts

[geekyMD]

Unfortunately, the deflection of a beam of light from a 1kg mass would be so infinitesimally small, that it would be nearly impossible to measure except over stellar or perhaps galactic distances, and how far from the center of the mass should the light be? This will influence the measurement also. They key is not to pick another arbitrary unit, but to explicitly define an existing constant, Avocado's [sic] constant, or Planck's constant.

Re:My thoughts

[Ashe Tyrael]

Aside from the fact that it's impossible to generate a perfect point mass. You can get almost there, or effectively there, but a point mass is impossible to generate in real terms. Zero-dimensional structures are by definition physical ideals.

Re:My thoughts

[geekyMD]

But a point mass should not be neccicary, the mass just needs to be perfectly sperical. So long as the distance from the center of the mass is greater than the radius of the mass + a few wavelengths to eleminate defraction, there should be no difference how the gravity field is generated. It simply needs to be uniformly constant for all points in every concentric shell larger than the mass. Am I right?

Re:My thoughts

[toddestan]

Aside from the fact that it's impossible to generate a perfect point mass.

Unless some discoveries have been made recently in particle physics, to the best that anyone can tell, the electron is a point mass (and a point charge too).

Re:My thoughts

[Hollins]

Yet check out the definition of an ampere, which involves "parallel conductors of infinite length, of negligible circular cross-section, ...".

This would seem to constitute a physical reference that is impossible to generate.

Re:My thoughts

[marcosdumay]

Thanks, but force has alread been define in terms of distance and current, we don't need another definition.
But if you can define the strongness of a gravitational field, we are done with the definition of mass.

Oh now...

[kwench]

... this will again take us into a century of nonunderstanding and confusion. Today, there are still some big nations that refuse to use kilogramm, litre, meter or celsius and prefer pounds, gallons, inch and fahrenheit.

How many rockets or other devices have disappeared or crashed somewhere just because scientists from one of these strange nations were involved in doing the programming?

Remeber, you heard it hear first: The end of the world is near...

Re:Oh now...

[Anonymous Coward]

Today, there are still some big nations that refuse to use kilogramm [sic], litre, meter or celsius and prefer pounds, gallons, inch and fahrenheit.

Only one, actually. Everybody uses SI except the USA.

I got your natural phenomena right here!

[BigusDickus]

"The kilogram is the only one of the seven basic units of the international measurement system defined by a physical artifact rather than a natural phenomenon."

Not entirely true.

The metric system originally was developed in France around the time of the French Revolution. The idea was that measurements used at the time had "royalist" origins. The foot was the length of some king's foot, the yard was the length from some kings nose to his outstretched thumb, and so on. The metric system was meant to purge these and replace them with measurements derived from nature.

The meter was originally defined as 1/10,000,000 of the distance from the equator to the north pole along the Paris meridian. The liter was defined as the volume of a cube 10 centimeters on each side (1 liter = 1000 cubic cm). Finally, the kilogram was defined as the weight of 1 liter of water.

Due to inaccuracies creeping in under various circumstances and the development of better measuring equipment, the current definitions were substituted for these original ones.

The metric clock they also came up with (10 hours per day, 100 minutes per hour, 100 seconds per minute) obviously never caught on.

Re:Not really...

[Anonymous Coward]

There is no precise definition for a litre of water.

WARNING: You'll have to pull your head out of your ass/arse to follow along.

1 m = distance light travels in 1/299,792,458 s
1 cm = 1/100 m
1 mL = cm^3
1 L = 1000 mL

I'm American. This isn't my native measurement system. You used the spelling "litre", implying that you're European. This should be your native system, and you don't even know what the hell a liter/litre really is?

Recursion to a limit

[tepples]

Recursive (adj): See recursive

You forget that Scheme gets along just fine with tail recursion as its primary looping construct, and a lot of things in mathematics are defined recursively.

A lot of things are defined as the limit of a recursive process. Start with Pa[0] being 1/600 of the pressure of the triple point of water. Then perform the following steps repeatedly, for n increasing without bound:

1. kg[n] is the mass of 0.001 m^3 of water at 101325 Pa[n] at the appropriate temperature.
2. Pa[n + 1] is 1 kg[n] m^-1 s^-2.

The limit of this recursion kg[n] as n tends toward +oo would be the kilogram.

experiment

[Anonymous Coward]

in what type of experiment is the *quantity* of the mass important?

I always thought that the m is variable in the equations, so specification on your definition of m does not matter. That's the trick physics always plays!

Atomic clocks use it

[poszi]

So how on earth is a watch manufacturer or repair person going to say "alright, the cesium atom vibrated 9,192,631,769... 9,192,631,770 times. That's a second."

The original definition of second was much much more difficult to measure (1/86400 of a mean solar day). Can you imagine a watch manufacturer making astronomical observations throughout the year to get the mean solar day? Now it is quite easy. The atomic clocks use caesium atoms for getting the accurate resonance frequency. Just get the atomic clock (or a clock synchronized with an atomic clock) and you get accurate time measurement.

At what pressure?

[tepples]

Liquid water is slightly compressible. Which pressure are you talking about? Pressure is defined in terms of force, which is defined in terms of mass, so unless you're willing to use some sort of recursive algorithm to define the kilogram...

Re:At what pressure?

[Jim Starx]

You would probably assume the pressure of an open container at sea level. Just my guess....

Re:At what pressure?

[tepples]

You would probably assume the pressure of an open container at sea level.

So how do you define sea level? Isn't that subject to change with global warming?

Re:At what pressure?

[Jim Starx]

Well, the water already needs to be at a defined temperature. So why not define sea level as the sea level at a point in the world who's current average temperature over a period of time (say the last year), is equal to that temperature at which your water will be fixed at.

Of course... this is all getting rather complicated... I like the idea of just defining planks constant to be a particular value.

But I thought

[ACNiel]

The metric system was the most fundamentally correct system of measurement ever concieved by man, beast or God.

You'd certainly think that reading all the hype on this bbs.

Remeber this article the next time a English/metric debate comes about. There is nothing inherently better about either system. That argument being nullified, should we switch based on the rest of the world? That is the only valid argument.

Don't start your argument, thought process, or comment with the mistaken common wisdom of "Everyone knows metric is better...."

And while I am ranting, but not quite as obvious, I don't want to hear 'I know what a kilometer is, I don't know what a mile is...' If you can pace off one, you can pace off the other. You certainly don't have an inborn sense of what a kilometer is anymore than you have an inborn sense of the mass of a plum sized chunk of some alloy.

Neither system is anymore natural than the other, get off your high horse and make a rational comment (unlike this rant ;).

Re:But I thought

[Anonymous Coward]

First off, think about the fact that the imperial system is actually based on the metric system. For example, the definition of an inch is 2.54 cm.

Remeber this article the next time a English/metric debate comes about. There is nothing inherently better about either system.

Yes there is. One system uses the same base for all units, and is made for easy conversions and calculations.

And while I am ranting, but not quite as obvious, I don't want to hear 'I know what a kilometer is, I don't know what a mile is...' If you can pace off one, you can pace off the other. You certainly don't have an inborn sense of what a kilometer is anymore than you have an inborn sense of the mass of a plum sized chunk of some alloy.

All the more reason to switch to the logical one. How many yards are 350 inches? How many gallons does a 3x3x3 feet cube hold? How many pounds are 234 ounces?
(the answers are 9.72222222, 201.974025 and 14.625, respectively)

Now let's try the same in metric:
How may meters are 350 centimeters? 3.5. How many liters does a 3x3x3 m cube hold? 27000 (or, preferred, 27 cubic meters). How many kg are 234 g? 0.234.

Re:But I thought

[thephydes]

There is no such thing as a fundamentally correct system of units. The only advantage of the metric system is that it uses base 10 rather than a mixture of bases, and hence is so much easier to use, and imo better. In Australia we changed over to metric in 1966. I stilll remember the old conversion figures ( as well as calculating ridiculously difficult problems either by hand or with my trusty slide rule). Belive me, the metric system is MUCH easier to use, although I still find some primal force in me doing conversions from L/100km to mpg - or maybe thats just to relieve the boredom of long car trips. I must say I find it quite amusing that a technologically advanced nation such as the US is still embracing a clearly inferior unit system, with sometimes expensive and embarrasing consequences. Or maybe there really are extra terrestrials out there that cause billion dollar space explorations to go crashing out of control into far away planets.

Re:But I thought

[Anonymous Coward]

Reason why SI rule:

How many gallons is a cubic foot?

Re:But I thought

[the pickle]

OK, YOU try converting a gallon into teaspoons without using Google. :-p

Dividing and multiplying by ten make a lot of sense. That said, I have no idea how tall "178 centimeters" is, or if weighing "70 kilograms" is anorexic, average, or fat for a person "178 centimeters" in height.

My favourite aspect of the metric system is conversions. It really *does* make conversions a whole lot easier.

p

Re:But I thought

[John Meacham]

The correct solution is to switch to base 12. Then we get easy conversions with the english system plus a more convienient base.

How often do you have to take 5ths of something compared to takeing thirds, fourths, sixths or halfs?

Re:But I thought

[Ashtead]

I hardly ever need to take 3rds, 4ths or 6th any more often than 5ths or 7ths or 13ths... or any other such accurate fractions of any numbers at all. As far as I am concerned, if we absolutely must change numeric base at all, base 16 would be better. We will still have 10 fingers no matter what, and dividing a pie has always been easiest by subsequent halving.

For the purpose of head reckoning, I find it vastly more useful to remember the decimal periods of the simple fractions for denominators up to about 16, and then further approximations for such things as a year being pi * 10^7 seconds, pi^2 is approximately 10, yet 100/pi = 32; the square root of 2 in terms of the fractions 1/7, 1/14 and their expansions, and so forth.

Similarly, the metric system carries with it the useful and expandable realizations such as a ton of snow will eventually melt into a cubic meter of water, or that a 1mm rainfall means that there is one liter of water per square meter of land. These prove useful and easy not just to remember, but to derive and expand on.

Re:But I thought

[vidarh]

The US officially switched to metric a century or so ago, though. It's just that they've taken a much slower approach to switching, by first redefining all the imperial units based on the equivalent metric units and then gradually requiring or allowing metric more places.

I think the Australian approach made more sense, personally.

Re:But I thought

[Laxitive]

The metric system isn't something groundbreakingly new, but an evolutionary improvement on older measurement systems. The argument is not nullified because one of the big advantages of the metric system is that a large portion of the world HAS switched to it. So as far as being a standard goes, it does better than the english system. And standards are useful. The only thing stopping the change is inertia, and some silly, misguided sense of measurement system nationalism.

-Laxitive

Just to state the obvious

[tod_miller]

They are cleaning the definition, not the value.

A new kilogram with equal an old kilogram. This will only make a difference to the history books and those who actually want to make thier own 'kilogram'.

I can imagine how many 'net savvy drug runners are looking at this and thinking, 'shit, I have snorted too much coke, does this affect my business? whats a planck? oh man, Avocado constant? [sic]

I say since the kilogram was an arbitrary measurement (in any definition) then why try and make it more formalised? I realised that celcius fit nicely with pure water at sea level freezing and boiling, and other measures have thier own basis (has the definitions have changed). Take my friend the meter. I always use the old skool definitions for rules of thumb.

Year Definition
1793 1 / 10 000 000 of the distance from the pole to the equator.
1795 Provisional meter bar constructed in brass.
1799 Definitive prototype meter bars constructed in platinum.
1889 International prototype meter bar in platinum-iridium, cross-section X.
1906 1 000 000 / 0.643 846 96 wavelengths in air of the red line of the cadmium spectrum.
1960 1 650 763.73 wavelengths in vacuum of the radiation corresponding to the transition between levels 2p10 and 5d5 of the krypton-86 atom.
1983 Length traveled by light in vacuum during 1 / 299 792 458 of a second.

So you see, a meter was the same in all these cases, but they just wanted to act clever.

The thing is, after world war 3, which measure will be easiest to revert to for a meter? trying to find scientist who can measure "Length traveled by light in vacuum during 1 / 299 792 458 of a second." or just comparing a brass stick with a length of wood while trying to build something using pre-existing specs (that you are relying on to build a post WW3 bridge). ;-)

Re:Just to state the obvious

[Jeff DeMaagd]

The definitions are done for scientific accuracy as the ability to measure improves.

Celcius is trickier than just temperatures of boiling and melting, because I think it must also declare the pressure too. The temperatures that water boils and freezes depends on air pressure. Kelvins are defined as divisions such that the range from absolute zero to the triple point of water is 273.16 kelvin. At least that doesn't depend on a the standard for pressure.

The problem with a meter standard depending on a physical object is that the length of that object changes with temperature. A temperature independent standard is needed. Standards that can be measured independently without having to refer to a specific single object are necessary for maximum accuracy.

Re:Just to state the obvious

[Anonymous Coward]

Was that a joke, or are you fucking dumb? Honestly, who teaches you such shit? Are you a sad result of the US-educational system?

Re:Just to state the obvious

[m50d]

It matters for precise physics. The reason it should be cleaned up is simply to stop it becoming 5E-6% smaller every year. People who don't need precision can still use artefacts, but some of us do need it.

Mod Parent Up

[Gabrill]

Someone smart famous once said "Any technology, sufficiently advanced, is indistinguishable from magic." These fundamental definitions are following the same path. Superbly and unarguably accurate, but also completely incomprehensable for anyone that doesn't have half a million dollars worth of sophisticated technology.

Weebles, and why "width of the thumb" failed

[tepples]

A unit is supposed to be a constant over a long period of time. If "kilogram" were 1/90 of your body mass, and I had a surgeon come and amputate your legs, then the magnitude of the unit would change radically. Likewise if I stuffed you full of pie. Centuries ago, when the inch was defined in terms of the width of the king's thumb, the inch-pound system of measurement had problems every time a new monarch took the throne.

Why has it still not happened?

[iamlucky13]

Even before the utility of having a fundementally defined unit of mass drives the necessity, I would think mere intellectual enthusiasm would. I'm honestly surprised that we hadn't already defined it. I can imagine a group of physicist and chemists somewhere coming to a group realization that one of the units they use the most isn't really anything.

meter

[POds]

Isn't 'the meter' also kept by some type of metal rod that basicly never changes? Basicly because i've heared they do adjust it every now and then :? I'd say it wouldnt be very often.

"The metric system is the tool of the devil."

[Hobadee]

"My car gets fourty rods to the hogs head and that's the way I likes it!"

Re:Not really...

[Anonymous Coward]

...and since we are discussing the metric system here... could you pls. telle us what 32 F and 212 F are in real world... preferably in C but I do also understand K...

Opportunitie$ for grant$

[tepples]

Even before the utility of having a fundementally defined unit of mass drives the necessity, I would think mere intellectual enthusiasm would.

Such research is expensive. Pure research predicated on "mere intellectual enthusiasm" is often less likely to get government grants than research based on scientific and technological need.

I can imagine a group of physicist and chemists somewhere coming to a group realization that one of the units they use the most isn't really anything.

The community had long realised that there was a problem, but they hadn't the pounds to fix the kilo.

Re:Opportunitie$ for grant$

[iamlucky13]

Well put! Thanks. A good reason, but I remain surprised it hasn't happened yet.

And the metre defined in round lightseconds...

[Anonymous Coward]

That would be a sweet overhaul. The metre redefined as light traveling during 1/1000 000 000 of a second.

That would really ease my great grand sons homework on galactic communication delays. I could like give him simple conversion advice straight from my head (in a jar on the shelf) and look all smart.

Natural phenomenon?

[Pedrito]

Man, I was confused. I thought a kilogram WAS based on a natural phenomenon. I thought it was how much coke Tony Montana could inhale in 1 sitting.

Earth Theory!

[Anonymous Coward]

1 Kilogram = 1000 cm^3 of Water (H2O) at 298 Kelvin grades.

open4free ©

Re:Earth Theory!

[iced_773]

Or you could do 1867. dm^3 C-12 at STP (101.3 kilopascals, 273 Kelvins).

Re:Earth Theory!

[jericho4.0]

That worked for a while, but the inaccuracies intoduced by getting exactly 1000 cm^3 water at exactly 289K (plus the correct air pressure) were limiting the measurments we could take.

Still, the intuitiveness of it is nice.

Re:Earth Theory!

[Anonymous Coward]

Who needs air pressure, or even the vapor pressure taken into consideration? Presumably it's in a 1000cm^3 box!

Circular definition

[thisisauniqueid]

From Wikipedia:

Avogadro's number, also called Avogadro's constant (N_A) is a large mathematical constant used in chemistry, formally defined as the number of carbon-12 atoms in 0.012 kg of carbon-12.

So the kilogram will now be defined in terms of a constant that is defined in terms of kilograms.

Re:Circular definition

[Anonymous Coward]

No, what you do is that you set Avogadros constant, to a....ehmmm...... constant (ie not dependant on KG). Then you define KG off that constant.

Mmm... 4?

[tepples]

n 1897 the General Assembly of Indiana, USA enacted in Bill No. 246 stating that Pi was de jure 4.

A bill in the Indiana General Assembly setting 3.2 and 4 as official rational approximations of Pi was passed by the state's House but tabled in the Senate.

That said, my favorite rational flavor of Pi is 355/113.

Re:Mmm... 4?

[Exatron]

That said, my favorite rational flavor of Pi is 355/113.

My favorite is apple.

Mod Parent Down

[Gabrill]

Gravity, regardless of strength, has no affect on mass. (At least until gravity becomes strong enough create singularities.)

Re:Mod Parent Down

[Burdell]

Gravity has lots of effect on mass. Usually it makes it fall down.

Re:Mod Parent Down

[Gabrill]

doh! you got me. I meant that the strength of gravity has no affect on the amount of mass.

Re:Mod Parent Down

[Anonymous Coward]

The proposal to redefine the kilogram based on the Plank constant would involve measuring how much electrical force it takes to keep the mass suspended in mid air.

The force of gravity on Earth varies depending on how far you are from the center. So if you make the measurement at the top of a mountain, the value will be different than if you measured in Death Valley (below sea level). I realize the difference is very small, but when you try to measure to eight digits of accuracy, the difference may become significant.

Re:Mod Parent Down

[suchire]

That's redundant. You were correct in the first place, as mass is a proportionality factor within momentum that is usually interpreted to mean the measure of the amount of matter.

Re:Mod Parent Down

[iamlucky13]

Mod me down? Troll? Typically such actions are reserved for comments that detract from the discussion. Even if I'm stupid, I'm still providing an opportunity for others to educate the stupid half of Slashdot.

From reading the article, it sounded like the plan was to determine the mass by measuring very precisely the force exerted by gravity on the mass. In that case, gravity is very important, because it will affect the measured force. Perhaps I'm misinterpreting the description of the method in the article, but I'm certainly not trolling.

Re:Mod Parent Down

[Anonymous Coward]

the first rule of trolling is always deny that you are trolling

Call me old fashioned but...

[illumnatLA]

I kind of like a standard unit of measurment I can hold in my hand or see with my own eyes.

African atoms?

[inode_buddha]

African atoms or European atoms?

I thought it was fairly simple...

[thebigmacd]

I know how the density of things change at certain temperatures but I'm going to talk a bout a liquid here, which doesnt change density much. In high school they taught us that 1 L of water is 0.1x0.1x0.1 m and weighs 1 Kg. That's pretty simple, and it fits with the other dimensions well.

Re:I thought it was fairly simple...

[vidarh]

Except that waters density DOES depend on the pressure, and the SI units to measure pressure depends on the mass. Hence the introduction of the international kilogram prototype to avoid a circular definition.

Re:Anyone Else?

[Anonymous Coward]

Don't be silly, that would be a "kibigram".

Re:Anyone Else?

[Tim C]

That's true, but that doesn't answer the question. They didn't pick a lump and say "whatever the mass is of this will be the SI unit of mass!".

The question is, all the other units are "base" units, while the SI unit of mass has a (kilo) prefix; how come?

Just remember that they replaced the meter

[gotr00t]

Before laser technology, the meter was defined as the distance between two markings on a bar of platinum-iridium kept in Paris. It was after Michelson invented his interferometer that the meter was redefined as 1,650,763.73 wavelengths of a certain orange line in the spectrum of krypton-86. This was later redefined in the 80's to be in terms of C, the speed of light.

As technology to measure substances to great precision increases, its about time the kilogram got a redefinition as well, one not based on a single object.

Their suggestion is lame

[Anonymous Coward]

Atoms don't have a fixed mass, so it would be rather dumb to base the kg on that instead of something else.

These people are on crack if they think the kg is changing.

Institute an exam for moderation rights

[alexo]

> mod parent up insightful

Huh?

Why in the world would anyone consider a statement of facts "insightful"?
What insight exactly was present?

Seriously, I believe that a prospective moderator should be made to correctly correctly identify possible moderation options before they can actually moderate submissions.

At least read the relevant FAQ entry before moderating!

On the other hand, almost every moron can vote (by virtue of their birthplace) so I guess that, in the grand scheme of things, SlashDot moderation does not really matter that much.

Yes!

[pyth]

Do it now!

Do it hard!

Re:Yes!

[rob_squared]

" Do it now! Do it hard!" Do it heavy?

Re:Anyone Else?

[tverbeek]

The question is, all the other units are "base" units, while the SI unit of mass has a (kilo) prefix; how come?

Because it was more convenient to create an object of 1kg mass than it would be to create one of 1g. Perhaps more importantly, a 1kg object was less likely to introduce error due to (literal) small sample size.

BASF

[Wyatt Earp]

At BASF we don't make the kilogram, we make the kilogram better.

It works in a hierarchy

[Anonymous Brave Guy]

Is there actually a method of directly using these definitions?

Where you actually need to use them directly, sure.

To give a real world example of how the standards work in practice... I used to write software for a company in the metrology (high precision measurement) business. They made machines that are used, for example, in quality control at the end of production lines. The gauges on the most popular machines gave accurate readings with resolutions of say 1-10m.

Those machines were calibrated from reference artifacts. These were themselves checked for accuracy on still higher precision equipment. (How they actually manufacture something so close to physical perfection is an interesting area in itself...)

Ultimately, there were white room areas with very careful decontamination procedures in place that were used almost exclusively for calibrating the company's most precise equipment and checking their reference artifacts.

From there, you were one step removed from the national standards laboratories. At that level the formal scientific definitions are just fine.

In other words, you work from major standards labs that can use the precise definitions effectively, and propagate the information (with some less, but little enough to be acceptable for the application in question) to more widely distributed testing facilities. A more trendy application of the same basic idea is the use of Internet-based real time clock services.

Re:It works in a hierarchy

[marcosdumay]

The grandparent made a good question. The fact that the other measurements can be made by the definition doens't implyes that a measurement can be made by the definition of mass by Plank's or Avogrado's constants.
In fact, this is the reason why those constants have not been already defined. This idea is not recent, I've hearing about that for ears, but nobody could never come out with a practical experiment to define any big mass constant.

Grrr... Slashdot filtering...

[Anonymous Brave Guy]

Looks like we lost a mu in there somewhere: the resolutions for the popular machines were around 1-10 micrometres.

Re:Base it on J-lo's butt

[Anonymous Coward]

funnier than mod gave credit for..

plus why mod down an AC?

mod parent down

[Anonymous Coward]

Nobody is with you. You are an idiot. You should be shot where you stand.

Old news?

[AvitarX]

I read something about this half a decade ago, there was a team working hard to make reproducable results within limits of collecting the proper number of ataoms to make a kilogram.

They were close but still a off by too many atoms (they wanted to be within some rediculously small number, and were like 3 times that away, I think the accuracy they were looking for wa in the realm of 100 atoms).

It really neads to be done so scientists can calibrate their equipment with masses as accurate as possible, and currently to get a true kilogram you need to get the official kilogram from France and in the prossess make it a little bit smaller.

Max Planck

[El Cabri]

This would amount to replacing the metric system by the Planck unit system. The metric system would be in effect to the new system what the imperial system if, for Americans, to the metric system nowadays.

And that would be a good thing.

Arthur C. Clarke

[Anonymous Coward]

I presume

By the way

[iced_773]

How many Avogadroes are in guaca-mole?

I guess 6.02x10^23...

Re:By the way

[Anonymous Coward]

dammit, i went three days looking for a post worth spending mod points on, and didn't use them at all...

and here I am, once again, without any points. Damndamndamn!!!

Somebody mod this guy funny!!

Re:By the way

[Anonymous Coward]

Consider yourself lucky. If you actually use your mod points carefully, thoughtfully, and fairly, then metamod will make sure you never get any ever again.

Re:By the way

[wavedeform]

Ouch.

Re:By the way

[Net_Wakker]

How many Avogadroes are in guaca-mole?
I guess 6.02x10^23...

Sigged.

In the limit

[tepples]

A kg defined in terms of a kg then becomes recursive...

But wouldn't such a recursive definition of the kilogram have a definite limit?

Re:In the limit

[Dun Malg]

A kg defined in terms of a kg then becomes recursive...

But wouldn't such a recursive definition of the kilogram have a definite limit?

Technically, the value will only approach zero, but never reach it. You can plot the curve out and calculate the area beneath it at whatever precision you like, but it's a non-terminating fraction. Physicists would never stand for any definition that depends upon such mathematical sleight-of-hand. They want a hard quantity defined in terms of other things.

Spiral

[tepples]

The pressure part really kills using water as a definition, because it has a mass component. Circular definitions are a no-no.

So how about a spiral definition?

Why not gravity?

[clambake]

Why not define it in terms of gravity? i.e. 1kg of mass is equal to the mass of a perfect sphere of platinum that can accelerate from rest another equally sized perfect sphere of platinium placed 1 metere away by X m/s?

Re:Why not gravity?

[Magic5Ball]

Nice, but implementing such a thing would be... uhm... difficult and it wouldn't be much different from the avorgado idea, or what we have now which is a cylinder of metal being accelerated the Earth at 9.8 m/s^2. For the masses you're considering, X is approximately 0 for any amount of platinum (or anything) we could fashion into a perfect sphere with current technology (ignoring the Pt/Ir supply issues).

Plus, perfect spheres made of soft metals have a tendency to deform when handled. Presumably this happens in a vaccum so that we don't have air friction, and also in freefall or low gravity so that we can ignore the friction of rolling.

While we're looking into the future, why not tie the kilogram to the amount of 1H required to convert into some specified quantity of energy?

Why the byte is not an 8th SI base unit

[iced_773]

This is kind of unrelated, but I think nobody here has said it yet.

The seven base units can be divided into smaller and smaller parts - a tenth of a meter, half a Kelvin, a zillionth of a second, etc. You can't do this with a byte, it just wouldn't work. Sure, you can have kilobytes and megabytes, but a millibyte?

As for the inconsistency with base-10 and base-2 units, I once read somewhere that they defined a new set of prefixes for the binary units, so a kilobyte would equal 1000 bytes while a "kibi"byte would be 1024.

Re:Why the byte is not an 8th SI base unit

[lgw]

the kibi/mebi/gibi prefixes give me the willies. Nevertheless, they're showin up in computer-related standards committees, so it's only a matter of time. :(

Re:Why the byte is not an 8th SI base unit

[Esion Modnar]

You can't do this with a byte

Not to nitpick, but I've heard of a half byte referred to as a nibble. But you're right, there's no smaller division (excepting the bit, of course) there. Just wouldn't make sense.

a "kibi"byte would be 1024.

Kibbles and bits, kibbles and bits, I'm going to get me more kibbles and bits. ;)
That would just cause more confusion. If you're reading something about kilobytes, you won't be sure if they're talking about the new version or the old version. Better to just call 1000 bytes a kibibyte. Nobody'll use it anyway, any more than kilometers are used in the US.

Re:Why the byte is not an 8th SI base unit

[maxwell demon]

Sure, you can have kilobytes and megabytes, but a millibyte?

Well, with bits it would make sense, if you speak about bits as a measure of information (-sum p ld p), not as a count of digits (as in "a byte has 8 bits").

Re:Why the byte is not an 8th SI base unit

[Zemrec]

I wish this was done a long long time ago. I've always hated the 2^10 bullcrap for *bytes. It doesn't make sense anyway as a computer doesn't really care if something is exactly some multiple of 1024 to be the next big unit. It only cares about bytes. The kilo/mega/giga/etc. is only for human readability anyway, so why not make it simpler for us mortals who can't figure how many bytes are in a gigabyte without using a calculator.

Re:Why the byte is not an 8th SI base unit

[ghjm]

I agree that there should be an SI base unit of information, but I think it should be the bit, not the byte.

Here is an example of a situation where millibits are meaningful:

Take 80 characters of 8-bit ASCII text. Call this P(0).

For each n from 1 to 999:
Retrieve 640 bits from a high quality random source. Call this R(n). XOR each bit of R(n) with P(n-1) and call the result P(n). Securely destroy all copies of P(n-1).

Having executed this process, you are left with the single value P(999) and the 999 values R(1)...R(999). For convenience, let's use a new naming scheme, Q, defined as follows: For 1..999, Q(n)=R(n), and for 1000, Q(1000)=P(999).

To retrieve P(0), use an accumulator, A, which is a variable of 640 bits all initially set to zero. For all n descending from 1000 to 1, XOR each bit of A with Q(n) and store the result in A. At the end of this process, the contents of A will be equal to the original P(0).

Because we can re-create P(0) using Q, the value of P(0) must be contained within Q. All elements of Q are required to retrieve P(0); if any single element of Q were to be lost, then P(0) would not be recoverable. No element of Q is more or less important than any other in the reconstruction of P(0).

How many bits of information from P(0) are contained in any single element of Q? The answer, obviously, is 640 millibits, or 80 millibytes.

The prefix "milli" is here used in the metric sense of 1000. I suppose it would also be possible to say that we had 625 mibibits. However, this presents a problem: With only the letters "mi" to indicate the prefix, how do we know if a mibibit is 1/1024 of a bit (related to "milli") or 1/1048576 of a bit (related to "micro")? Do we have to resort to milbibits and micbibits, or millibibits and microbibits?

This message is 1934622720 micbibits in length.

-Graham

Snort pepsi instead

[tepples]

From now on, a kilo is the amount of coke a mexican hooker can snort in one week.

Why not pepsi?

Or course, that is under STP.

I am, I am, I am, I said I wanna get next to you...

Well, duh...

[CrazyDuke]

Why not define a gram as the mass equivilant to the mass of one mole of hydrogen (the proton-electron isotope)? ...and a kilogram is just 1000 grams...

You know, Avogadro's number? It's mentioned up top in the summary. KISS

It's all about the Bases

[Cliff.Braun]

The only reason that the metric system is better is because it uses base-10 to convert between units, to convert from inches to feet to yards to miles one has to multiply by 12, 3 and 1760. TO convert from centimeters to meters to kilometers one has to multiply by 100 and 1000 you tell me which you'd prefer to do? Measures of volume in the American(had to refrain from calling it the idiot system as one of my teachers did) system make more sense, they are basically base-2, but they throw quarts in just to throw you off. Whereas metric is base-10 again. As you say, there is no inborn sense of which is better insofar as you can't instinctively measure one more easily, unless you are a dead king. However it is much easier for a human to multiply by 10 rather than 12 or 3 or, heaven forbid, 1760. The other good thing about the metric system is that if you dont know how to convert between two units, you can tell pretty easily, assume you dont know anything about mass measurements, if I tell you to convert from grams to kilograms, you are much more likely to be able to do it than ounces to pounds. I have the conversion factors memorized for weight, for, uh, reasons. I guess metric Isn't better, but it is much easier.

Re:It's all about the Bases

[amliebsch]

The only reason that the metric system is better is because it uses base-10 to convert between units

THIS IS EXACTLY WRONG. In fact, this is why the imperial system is still in use - because it is largely base-12 in nature. Base-12 is far superior to base-10. The only advantage to SI metric system is that it is CONSISTENT in its conversions, where the imperial system is not. But using Base-10 for those conversions is a major headache, especially for bakers, carpenters, and anybody who has to frequently divide by 2, 3, or 4. The BEST system would be a metric/SI system that uses base-12. But I'm sure the Base-10 bigots will find reasons to disagree.

Re:It's all about the Bases

[the pickle]

Here's a real simple reason:

We don't have 12 fingers.

A base-12 measurement system will never succeed until we start teaching everyone to count in base-12 from birth, and to do all their math in base-12.

p

Re:It's all about the Bases

[amliebsch]

Logical fallacy. Appeal from popularity. Irrelevant to the merits.

Re:It's all about the Bases

[Anonymous Coward]

Popularity is rather important for communication.

Re:It's all about the Bases

[m50d]

The only factor that makes sense to use is a factor of "10". Why? So you can take zeroes off and add them to convert. It doesn't matter whether this "10" is actually 0xC or 8 or whatever, but the conversion should be a factor of 10. Until people are willing to junk the arabic numerals and go for hex or sexagesimal or something sensible like that, metric is the only system that makes sense.

Re:It's all about the Bases

[Markus Landgren]

So why do you call your superior system "base-12" as in "base-(1*10^1+2*10^0)"? Here's why: Because base-12 masochists enjoy mixing base-10 numbers with base-12 units.

Re:It's all about the Bases

[SamSim]

Not only is the imperial system inconsistent, using 2s, 3s, 4s, and 6s instead of 12s a lot of the time, the inch is divided into sixteenths, there are 16 ounces in a pound, 14 pounds in a stone, 2000 pounds in a ton... I would have infinitely greater respect for the imperial system if it was all 12s. But it ain't.

Besides which, we use decimal. Ultimately, you're going to end up down at fractions of the smallest possible measurement where you have no choice but to use decimals to express your figures. If we ran on a base-12 number system, that would be fine. But we don't.

Re:It's all about the Bases

[natrius]

If you named all the bases in their own base, they'd all be base-10.

Re:It's all about the Bases

[medep]

why is a 12 base system better? our number system is base 10 or perhaps base 2 if you're a slashdotter. the very fact that you're using the number 12 to denote twelve is testament to the fact that you use a base ten number system yourself. it's like the joke: there are 10 types of people in the world, those who understand binary and those who don't. please enlighten us why twelve is a better number than ten. dividing base 10 numbers by 2 or 4 is usually easy, and changing for the sake of dividing by 3 or 6 seems a bit of an overreaction. in the meantime, feel free to implement such a system. wouldn't bother me, i'd just write a script or something

Re:It's all about the Bases

[medep]

good point. it all depends on one's definition of 10

Re:It's all about the Bases

[Colonel Cholling]

If you named all the bases in their own base, they'd all be base-10.

You don't have your own base. All your base are belong to us.

Re:It's all about the Bases

[j_heisenberg]

If we had 6 toes and fingers, I'd completely agree.

Re:It's all about the Bases

[Scarblac]

Base-12 is far superior to base-10.

I thought everyone agreed that base-10 was perfect, they just don't agree which base "10" is in...

Re:It's all about the Bases

[hankaholic]

But using Base-10 for those conversions is a major headache, especially for bakers, carpenters, and anybody who has to frequently divide by 2, 3, or 4.

Baking is always cited as a reason for using imperial units. I enjoy making bread on a regular basis, and occasionally other baked tasty things, and let me tell you the Imperial system is virtually worthless when dealing with flour and to a lesser extent sugar and salt.

Any good bread recipe targeting the average American baker will usually state something to the effect of "3 to 4 1/2 cups of flour". That's not because the person writing the recipe didn't feel like specifying greater accuracy -- it's because volume is a horrible way of measuring flour.

To properly measure a cup of flour involves fluffing up the flour, gently filling your measure, and sweeping the excess off of the top. This is a pain and a mess -- you try effectively fluffing flour without creating a dust cloud, keeping in mind that this will often be done in a kitchen and that a cloud of flour is quite easy to ignite. Even when consistent measuring techniques are used the amount of flour in a given volume can vary considerably due to other factors, including the mill of the flour itself.

Generally, the experienced bread maker will start with an amount of flour that they know to be less than what they need, and work in extra flour as needed. This works with breads meant to be chewy, but as working the dough makes it more elastic this is less than ideal for more delicate items such as biscuits.

Things are further complicated when using volume to measure salt or sugar -- flake size can vary significantly, and the amount of variation in a tablespoon of salt (especially kosher salt, which has a generally large flake size and is easier to work with in the kitchen) can make a notable difference in the final flavor. Equal weights of sugars provide equal sweetening, but a cup of white sugar, brown sugar, and confectioner's sugar might weight 200, 220, and 120 grams respectively. Again flake size within the individual types of sugar varies from manufacturer to manufacturer. In addition to changing the texture and flavor of the product sugar affects the rise time and quality when yeasts are involved. Too much, and the product will expand too much, ruining the texture. Dough for breads is often worked, left to rise for flavor development, and then shaped into its final form and allowed to rise again. Too little sugar, and the dough's first rise may be its last, leaving you with a surprisingly dense and hard dough brick after baking.

By purchasing a quality digital kitchen scale, the baker can place the container to be filled on the scale, "zero out" the scale (which tells the scale to treat the reading it is currently getting as its "zero mass" point), and fill the container to the desired amount. This leads to easier conversion between various types of sugars, salts, and flours, including unintentional conversions when your particular brand of kosher salt has a larger flake size than that used by the person who wrote the recipe.

I just don't follow the justification that bakers have to commonly divide by 2, 3, or anything for that matter. Few people find, say, 1/3 cup by starting with a cup and dividing it into three parts. Even something such as filling a one-cup measure exactly halfway with flour or moleasses is quite difficult!

I'd say that it's just as easy given the proper tools, and more accurate in terms of the actual amount of the ingredient involved, to measure 50 grams of sugar as it is to measure 1/4 cup. In either case, nobody is dividing anything, simply using the proper measuring device. In the case of the recipe calling for 40 grams of sugar, though, the SI system has a clear advantage. The SI baker would add to the scale until it read 40g. How about 40 grams of sugar (80% of 1/4 cup) in terms of standard Imperial measuring devices?

Google calculator gives "80% of ((1/4) US cup) = 4

Re:It's all about the Bases

[Markus Landgren]

That's exactly the point. Base-10 is superior regardless of whether "10" means ten, twelve, sixteen or two. What's not superior is mixing one number system with another. If you want base-twelve units, then use base-twelve numbers and go from there.

Re:It's all about the Bases

[Reverend528]

But Base-12 isn't easily divided by 5. Clearly, the best system would be base 60. It would then be easily divided by 2, 3, 4, 5, 6, 10, 12, 15, 20, 30.

Re:It's all about the Bases

[the pickle]

Call it a logical fallacy if you want, but it's precisely the reason the US has never switched to the metric system.

p

Re:It's all about the Bases

[RedWizzard]

Clearly, the best system would be base 60. It would then be easily divided by 2, 3, 4, 5, 6, 10, 12, 15, 20, 30.

That's why there are 360 degrees in a circle.

Re:It's all about the Bases

[jdmetz]

You'll put the "Low-Sodium" salt makers out of business! I came across a container of "Low-Sodium" salt in the grocery store and had to compare the nutrition information. Indeed, it had 2/3 the sodium per 1 teaspoon serving of the similarly shaped "regular" salt container next to it. And, the net weight of the container was 2/3 as much. Not only this, but this salt that takes 50% more volume for the same weight also cost 5 times as much as the "regular" salt. If people in the US measured salt by weight rather than volume, they could no longer make a fortune off of low sodium diets.

To not upset my wife

[Anonymous Coward]

I have to post AC. Why not just calibrate it to the weight of my male member? (It's close enough)

Re:To not upset my wife

[Anonymous Coward]

They said kilogram.

base it on known units

[cats-paw]

we have a very refined measurement for a meter.

we can measure atomic spacing very accurately.

why can't the kg, be based on a certain crystalline form of some material in a box shape with particular dimensions ?

I pick silicon. so using a particular crystalline form, create a cube which is x & y & z meters on a side.

there are x numbers of atoms, so now we know have a reproducible unit of mass.

here's another thought.

how accurately can gravity be measured ? how about a given amount of material which generates a particular force. ultimately this would be most relevant definition, since the curvature of space, i.e. gravity, and mass are so closely related.

Re:base it on known units

[Anonymous Coward]

I pick silicon. so using a particular crystalline form, create a cube which is x & y & z meters on a side.

Right, and you do this without bad spots, with 100% purity and without it oxidizing on the surface, and then you win the Nobel prize. But please - just do it and don't talk about it, or we might get the expression that you don't know what you're talking about.

To Wash or Not to Wash?

[vortex2.71]

Yeah, the arbitrary kiligram is very antiquated... I've heard these guys get together and spend months discussing whether "the kilogram" should be washed and how. Washed to often and the weight will decrease, too much and it will pick up dust and increase in weight. Atoms are much more standard.

ObDoes This Mean

[whimsy]

I can return my ancient reagents that are sold in bottles containing "one mole" since the mole changed?

French

[coopseruantalon]

Because the alternative is to use something the french came up with...

Re:French

[BarryNorton]

I should give up speaking English, too, if I were you; a good deal of that came from the French. Seems like you've already made a start though...

Re:French

[coopseruantalon]

Actually i'm from Denmark...

Re:French

[BarryNorton]

Fair enough - a land of more reasoned Euroscepticism, in my opinion. (And at least you didn't give yourself a capitalisation either!)

Re:French

[coopseruantalon]

Ah so that was what you were referring to. You had me confused there. Euroscepticism has unfortunately declined here recently... Somehow people are just inclined to like softwarepatents, buearcracy(?), agriculturalsubsidies and the like.

Just leave the RCH alone

[GomezAdams]

First the kilogram then who knows where next. You can dick around with the gram if you like but leave that most hallowed of engineering terms alone.

Just a few corrections

[Alexei]

A hectare is 2.5 acres, so there are 40 ares in an acre. An american pint is .475 L, very close to .5 L. A German pound is 500 g, whereas american is 454 g.

Re:Just a few corrections

[4phun]

The German pound is always heavier because the German butcher has his thumb on the scale.

How about water?

[Ironsides]

Why not just give the definition of 1 kg as a certain number of water molecules? Water seems to be the universal substance in the metric system. (1 gram water being in volume equal to 1 centimeter^3 at a certain temperature). Just define it using water molecules and complete the circle.

Re:How about water?

[Anonymous Coward]

Bad idea - how are you going to count 'em water molecules?

Good idea - learn some chemistry/physics before giving advice to scientists.

Re:How about water?

[Ironsides]

How do you count Avagadros number? Besides, I'm just expanding on one already sugest by the scientists themselves. either a quantity of light or the mass of a fixed number of atoms. Water goes along witht the second part. Had chemistry, had physics. Have had more than most people.

Calibration

[nuggz]

Why even try to make something perfect?

What we do for precision work is make a master near the size we want to be, and then just be sure to consider the offset.

Re:Calibration

[ph43drus]

Ever tried measuring the mass of a neutrino? Yeah, it's pretty damn hard. The easiest way to do that is to watch the beta decay of the tritium nucleus and make precision measurements of the products' and reactants' momentum. The only one you can't really measure is the neutrino itself, but a certain percentage of the decays give you data that you can reduce such that you can plug the results into an equation for the neutrino mass.

There's a problem with this equation. The mass of the tritium nucleus and the helium-3 nucleus need to be subtracted off to get the neutrino mass. The upper bound on the neutrino mass is 2eV. Both those nuclei are approximately 3GeV. To get the error to work out, you need the nuclear masses of the tritium and helium accurate to the parts per trillion range.

In other words, before you can measure the neutrino mass, someone needs to push as hard as possible for perfect measurements of the tritium and helium-3 nuclear masses.

Jeff

Clearly they should set it to be

[Anonymous Coward]

Clearly they should set 1 KG to equal 1 American Lb. Then they can upgrade the rest of the broken metric system to the correct American units.

One KG should equal...

[Anonymous Coward]

One pound

Re:Not really...

[Tomfrh]

Yes I am aware that 1 litre equals 1000 cm^3.

But the number of water molecules you can fit into 1000 cm^3 depends on many things, and that is why I stated that there is no precise definition for a litre of water.

Retaliation

[PsiPsiStar]

Isnt the International standards organization located in France?

This is just a runner up to 'freedom fries.'

... even the inch

[Evil Pete]

... is defined as being 25.4 millimetres as I recall.

The size of a plum?

[Anonymous Coward]

What do you mean? An African or European plum?

-1: Trivial Google search

[p3d0]

"Official definition of the meter"

Not entirely true

[vlad_petric]

Almost all science in the US is actually done in SI. Why ? Simply because the imperial system is incomplete.

1 Volt, for instance, is 1 kgm^2s^3A^1. It has both the meter and the kilogram in it. There is no imperial equivalent for it. Messing around with both SI and imperial will only lead to problems (IIRC a Mars probe failed because of "conversion errors").

Re:Not entirely true

[Anonymous Coward]

It's not incomplete, it's just that MKS is a whole lot easier to do math with.

Your example would work just as well with imperial measurements - 1V = 2.20462262lbs*3.2808399ft^2*s^(-3)*(6.25*1018/s)^( -1).

By the way, just to be accurate, keep the signs straight in your exponents. Your definition of a volt is wrong.

Measure mass instead of weight

[Velox_SwiftFox]

Use a balance instead of a scale.

I thionk that they have scales that jiggle things and determine mass from inertia too.

Re:Measure mass instead of weight

[Jim Starx]

Measuring inertia is the same as measuring weight. Your just measuring the force due to acceleration instead of the force due to gravity. And a balance is used to determine that the weight of two objects is the same. But I'll admit the balance fairs better then a scale because there doesn't need to be any calibration with respect to the force of gravity at whatever location you're at, it just divides out of the equation. But blances still need to be "calibrated" in the (loose) sense that you need balancing weights who's mass has been pre-determined. The problem with a balance is that it can't be used from the ground up, it requires some previous measurement of mass to have taken place.

But...

[RobinH]

I always thought one cubic centimetre of water at standard temperature and pressure had a mass of 1 gram. I guess it's not already defined that way?

Re:But...

[vidarh]

A gram has always been defined as 1/1000th of a kilogram - kilogram is the base unit, not gram. A kilogram used to be defined almost like you say, but it was changed in the 1880's or so.

Missing the point

[Zaak]

The discussion so far has focused on the redefinition of the kilogram. However, the point of the article was not to argue for the redefinition, but rather to argue for redefining it sooner rather than later.

Every informed person agrees that the kilogram needs to be redefined in terms of physical constants, and several projects are underway to make this possible. However, these projects are not currently able to define the kilogram with as much precision as the current kilogram object can be measured.

The article is arguing that the benefits of a physical constant based definition of the kilogram are enough to outweigh the temporary loss of precision in the definition of the kilogram.

Hmmm...

[aztracker1]

Losing "mass" ... may have to look into that viagra spam, etc... (too funny to pass up)

Hasn't This Already Been Done?

[Anonymous Coward]

Excuse my ignorance, but isn't a liter of pure water equal in mass to one kilogram? What's the problem?

Re:Hasn't This Already Been Done?

[Anonymous Coward]

No. Fuck off. Educate yourself before posting crap. Is education in the US *that* bad?

oh, no. let's not let this trend spread!

[anothy]

look, we're all used to it in the CompSci world by now, so we might not realize how bad an idea it is, but do you understand how bad a mistake it will be to allow them to redefine a kilogram to be 1024 grams? we must stop this!

Re:oh, no. let's not let this trend spread!

[tinkerton]

how about 1021 grams then. That's for a live kilogram . 1000 is for a dead kilogram.

What is the alloy's vapour pressure?

[funtime]

Every substance has a finite vapour pressure, so couldn't the standard be losing weight through sublimation? Can't imagine it would be as much as the 50 micrograms per century, though...

A quantity of LIGHT???

[Caspian]

How many photons does it take to mass one kilogram? I'd imagine roughly a metric fuckton.

No, a pound is a unit of mass

[DavidHopwood]

You're mistaken. A pound avoirdupois (symbol lb), which is what is usually meant by "pound", is defined as exactly 0.45359237 kg, and is definitely a unit of mass.

The meaning of "weight" is ambiguous between "force due to gravity" and "mass". In commerce, it has always referred to mass. (If you want to measure the quantity of something, you balance it on some scales against a known reference mass. Force can't be measured nearly as accurately or conveniently with simple equipment.)

You were probably thinking of a "pound-force" (symbol lbf), but that is a deprecated unit with no precise formal definition -- since it would have to depend on some arbitrary average value of g at the earth's surface. Sometimes a conventional value of g is used that comes out to 1 lbf ~= 4.448 222 newton, but that's not a standard.

Re:No, a pound is a unit of mass

[biglig2]

Er, if you're using a scale then you're measuring force, though.

God, this is so pedantic, and I'm just making it worse...

Re:No, a pound is a unit of mass

[ikkonoishi]

Depends on the type of scale.

A balance scale measures one mass against another and ignores gravity in its calculations. (So long as it has gravity to keep the weights on it.)

A spring scale measures weight and can vary according to gravity force.

This link explains it pretty well. Basically weight is ambiguous due to misusage.

Re:No, a pound is a unit of mass

[ChaoticLimbs]

Scales of any type are incapable of measuring mass unless they are completely within a vacuum. Otherwise, results are skewed by you measuring them with respect to the weight of the air they're in. Everything has some bouyancy in air, but its mass overwhelms that for objects heavier than air.

Re:No, a pound is a unit of mass

[DavidHopwood]

Right, but the density of air is approximately 1/800 that of water. So simple unenclosed balance scales would have been (and still are) sufficient to measure masses for essentially all commercial purposes, and some scientific ones.

Re:No, a pound is a unit of mass

[biglig2]

Well, it's an interesting link, the trouble is that the person at the other end is wrong.

A balance is a device that compares two forces to see if they are equal. It tells you nothing about masses directly.

I suppose that, if both forces are being generated by a mass proportional force field acting on two masses, one on each pan, then you could use it to deduce that the two objects are of equal mass, but so what? Deducing something is not measuring it.

The very fact that the link points out, that you can distort the results of the device with the butcher's thumb, is itself a demonstration that the device is measuring force, not mass.

What if I took a balance into zero G and applied a strong electrical field to it. Oh look! now it's not "measuring mass", it's "measuring charge".

Actually the page is about confusion over what pound is a unit of. Physicists have no confusion about it at all; mass is in kg, force in newtons, sweeties from the corner shop in quarters of a pound. Easy!

Be very, very sure

[stewwy]

..... that what you use to define a constant with doesn't change with time otherwise how do you know which has changed? I remember reading a SiFi story where the universe was shrinking to a point and because it was all contracting at the same rate and all the known constants where the same nothing was noticed until the last few seconds. This is the point at which physics becomes meta-physics.

international team of scientists

[riqnevala]

They are getting too big a salary for the nonsense they are arguing about. How about developing non-polluting energy-sources instead? How about flying cars?

Actually...

[Grendel Drago]

Not to nitpick, but I've heard of a half byte referred to as a nibble.

You mean nybble , don't you?

--grendel drago

Re:Actually...

[stormhair]

... you do realise that link redirects to Nibble, don't you?

Just wondering

[Lightning Hopkins]

What are the other measurement artifacts, and what do they measure? There's a book I'll probably never get around to reading (because I've got a stack of others to which I'm constantly adding things of more immediate interest), "The Measure of All Things" about the adventures that were had in attempting to properly measure and define the meter, which probably explores at least some of it.

mass unit sould be the mass of one proton

[phatsphere]

i suggest to use the mass of one single proton as the base unit. and then a fixed factor to get 1kg of it. that would be the only solution which would hold for a long time...

What? It's based on water!

[Anonymous Coward]

The only 'contrived' part of the metric system is the metre, and it's been pegged against the speed of light (so even relativity won't change it). Originally the meter was set so that 40,000 kilometres make up the circumfrence of the earth (and for all intents and purposes it still is). 1/10 of a meter is a decimeter. 1 decimeter cubed is defined as 1 litre (unit of volumetric measure). If you fill a 1 litre container with pure water at 0 degrees celcius (where water freezes), it weighs (by definition) 1 kilogram (and 1000 kilograms is 1 metric ton). I've never ever heard of someone using a 'plumb object' or other for 'the official kilogram'.

A kilogram is not abitrary.

[Jake Dodgie]

I thought that 1 kilogram=1000 gram

1gram=the weight of 1 ml of pure water at sea level

ie it's not an abitrary unit of measure, just the representation of as alump of platnim is abitrary, it could have been gold, lead or any other long lived metal.

Re:A kilogram is not abitrary.

[vidarh]

You're wrong. 1 gram is defined as a thousandth of a kilogram, and a kilogram is defined as the mass of the kilogram artefact.

The definition was originally that a kilogram was the mass of one litre of pure water at 4 degrees Celsius and standard athmospheric pressure, but that is a circular definition, as the definitions of the SI units for pressure depends on mass.

As a result a kilogram is now the mass of the kilogram artefact - if the artefacts changes mass, it still remains 1 kilogram

Re:Not really...

[Jake Dodgie]

1 meter = one ten-millionth of the length of the earth's meridian along a quadrant (one-fourth the polar circumference of the earth). In 1791, the French Academy of Sciences selected the meridional definition, using the meridian of Paris.

puzzle

[jago25_98]

What gets lighter but wieghs the same?

Funny thing is it's just a block of metal kept in a glass case. Every year it gets lighter relatively, but in absolute terms it remains the same :p

"The international standard for mass is the International Prototype of the Kilogram kept at the International Bureau of Weights and Measures (BIPM) located in France. It is the only measurement standard today that still relies on an artefact. (The other SI units are derived through fundamental physical laws of nature and quantum physics.) "

Re:Anyone Else?

[Tim C]

You're probably right, but then what is there stopping them from saying "This mass is the standard kilogram. The gram is exactly 1000th the mass of it"?

After all, that *is* what they're saying effectively, yet the kilogram is the SI unit of mass, not the gram. (In the same way that the joule is the SI unit of energy, rather than the millijoule or kilojoule).

That is, I'm not asking why they didn't create a standard gram mass, rather why does the SI unit of mass, alone amongst all such units, have a prefix?

USD - EUR

[Anonymous Coward]

Well.. 1 EUR is about 1.3 USD these days... we should also have EUK en USK (european kilogram and us kilogram). As the average american is about a third heavier as the average european. That way americans can still keep their egos and say they are 90 kilograms iso 120 ;-)

agreed. plus a correction

[tinkerton]

However, these projects are not currently able to define the kilogram with as much precision as the current kilogram object can be measured.

Maybe what you thought you were writing is not what I think i am reading, but I dislike this phrase, so I'll try to unravel it(at the risk of making things worse).

A definition is exact, infinite precision.
When you're using either Planck constant or Avogadro's number, once you're changing the status of one of them from a physical constant to a defined constant, their values are exactly what they are "because we say so".

The problems are here:

Definition and conversion problem: that's the scientist who asks "okay , I wrote in this article that object A has weight X. What's that in new units? I never used Avogadro's constant because it was so crude." Nobody knows how many atoms there are in the Paris standard specimen. What exact value shall we define the constant to be so we don't have to bother too much with older experiments.

Calibration problem: you have an absolute definition of a kilogram: count A atoms. But where previously you could say "Marie, go to Paris and calibrate our kilogram.", Manuel the atom counter here keeps coming up with different numbers each time and it's not his fault. Or so he says.

The main problem is one of calibration.

NIST

[belg4mit]

NIST release
http://www.nist.gov/public_affairs/newsfr omnist_re def_kilogram.htm

Personally, I prefer NIST's prior stance, an electronic kilogram:
http://www.nist.gov/public_affairs/gall ery/kilogra m.htm

Another joke ...

[Anonymous Coward]

What do you see when a mole of moles are digging a mole of holes?

A mole of mole-asses!

British Pint != American Pint

[CBDSteve]

Do you realise that the definitions of Fl Oz, Pints and Gallons are different in America and Britain?

A British Pint is .568 of a litre, whereas the American one is 0.473 (so the definition of a gallon is different).

Fluid Ounces (fl oz.), too - there's 20 in a UK pint, and 16 in an American pint.

I think the American version is actually the original one - us Brits changed our measurements some time after the Revolutionary War, while the US kept them the same.

Re:British Pint != American Pint

[Moderatbastard]

The sizes of the pints pretty much cancles out the 16/20, so the fluid ozis near enough the same. Different parts of England had different gallons, it wasn't standardised (as the volume of 10 pounds of water) until Queen Anne's time.

Re:British Pint != American Pint

[pnewhook]

I think the American version is actually the original one - us Brits changed our measurements some time after the Revolutionary War, while the US kept them the same.

Actually the difference between american and british gallons traces back to when britain owned America and enterprising captains ran trading ships between the two countries.

To make more money, the captains would transfer the contents of the larger british gallon barrels (ususally 5, 10, 20 gallons or more) into slightly smaller barrels en route and sell them to the Americans as full size. Since this was common practice, the Americans eventually accepted the smaller gallon as 'real'.

The definition of a Kilogram: water

[Midnight Thunder]

According to the glossary at the Hawai'i Institute of Geophysics and Planetology, the definition of one Kilogram is as follows:

One kilogram is equivalent to 1,000 grams or 2.2 pounds; the mass of a liter of water.

You're from the west, aren't you?

[DancesWithBlowTorch]

The sizes are: 0.2l for Kölsch and Alt. 0.3l for some kins of "Pils" which consider themslelf noble. 0.4 for a standard everywhere pils,a nd your pint is just between 0.3 and 0.4. The enxt size is 0.5l for Weiten.

You must be from the Rhine-Ruhr Area. In southwest germany, people buy half a litre of beer. In Bavaria, it's typically simply one litre (a "Maß"). I think the litre is a fine volume measurement for alcoholical beverages. It just depends on where in the world you live and how much alcohol is deemed to be appropriate by society. :-)

Re:It's all about the Bases - hah! best quip !

[Anonymous Coward]

thanks. best joke i've seen in about 3 months of searching.

(yes i get my entertainment mainly from slashdot)

Let me guess...

[jotaeleemeese]

Death penalty?

Incarcerating people without trial?

Extrajudicial killings?

Dunow, it is eluding me....

Killer Hangover in Hanover

[Anonymous Coward]

Apparently you are still hung over, judging from your bears, haufrbaus, aidelwieses and South Terrols! Oh, the terrol!

My vote

[Bohemoth2]

Is for the Avacado number. ;)

Re:Anyone Else?

[Moderatbastard]

In summary, the kilogram is the basic metric unit of weight, not the gram.

Neither the gram nor the kilogram is a unit of weight in any system.

Who'll count?

[ediron2]

scientists suggest replacing the kilogram artifact -- a cylinder of platinum-iridium alloy about the size of a plum --with a definition based on one of two unchanging natural phenomena, either a quantity of light or the mass of a fixed number of atoms.

Geek1: Six hundred two sextillion, two hundred fourteen quintillion, one hundred ninety eight quadrillion, nine hundred ninety nine trillion, nine hundred ninety nine billion, nine hundred ninety nine million, nine hundred ninety nine thousand nine hundred ninety. Six hundred two sextillion, two hundred fourteen quintillion, one hundred ninety eight quadrillion, nine hundred ninety nine trillion, nine hundred ninety nine billion, nine hundred ninety nine million, nine hundred ninety nine thousand nine hundred ninety one. Six hundred two sextillion, two hundred fourteen quintillion, one hundred ninety eight quadrillion, nine hundred ninety nine trillion, nine hundred ninety nine billion, nine hundred ninety nine million, nine hundred ninety nine thousand nine hundred ninety two. Six hundred two sextillion, two hundred fourteen quintillion, one hundred ninety eight quadrillion, nine hundred ninety nine trillion, nine hundred ninety nine billion, nine hundred ninety nine million, nine hundred ninety nine thousand nine hundred ninety three. Six hundred two sextillion, two hundred fourteen quintillion, one hundred ninety...

Geek2: Whatcha doin', man?

Geek1: Um, I'm about done recalibrating this universal standard kilogram. Just got a... um... er... shit. One. Two. Three...

The reals problems are geometry and purity

[madsh]

Last time I saw a note about the problem (nature some 4 months ago I think...) two problems where mentioned.

One aproach to remove to relatitivy of the mass definition is to define the kilo as the weight of a number of atoms. The solution suggested was based on a sphere of pure crystalin silicon, and here the problems starts...

The sphere has to be as close to perfect as possible. And for the time the most perfect spheres produces are floating around in a satelit messuring some Einstein Relativ Gravitational force. The accuracy of these spheres are in the size that the accuracy of the silicon sphere definition is no better then current 50 microgram tolerance.

I am guessing the the problems creating a perfect sphere also applies to the production of a near to perfect cylinder.

Even if it was possible to make a very-close-to-perfect sphere it is still very hard to make sure that it contains only one kind of atoms. The purity of scentific grade silicon is very close to perfect, but even with very small fraction of different atoms the weight will again be off. And without new and better methods for producing pure silicon the tolerance will add up to about the 50 micrograms.

And again I am guessing the producing pure silicon crystals is no harder then producing any other long lasting composite alloy.

So I think we a stuck with a brick in jar in Paris for another decade or two...

Salami in decagrams

[Anonymous Coward]

When I was living in Europe I had to buy my salami (cheese, ham, etc) in decagrams. So I can tell you, they wouldn't sell you 80 grams of salami -- doesn't make sense. Now, 100 grams -- that, they would sell you (but only if you called it "10 deca"). Barely is enough for one sandwich, though -- I suggest you go with 20 deca as a minimum purchase for items like ham and salami.

And buying butter in chunks of 500 g is quite normal.

I cannot speak for all Euro nations, as I was living in only the one, but it's a good guess that it wasn't the only one that sold its deli items in this way.

Re:I suggest [Slightly Off Topic Sorry about that]

[Coeurderoy]

himihergotsakelzement, I stand corrected, I guess I should have drunk a Mass or two before so that I would clearly see the s in double :-)

Itime

[KiloByte]

If you want metric time, you should check out itime, a new "standard" that Swatch tried to push in. It defines the day time as a real number 0<=x<1000, with 0 being the midnight in Switzerland.

Of course, it take a lot less effort to stick with the good old standard devised by ancient Babylonians, mentioning just the time zone when needed.
Personally, I'm sticking with time_t (number of seconds past Epoch).

Avogadro's number is NOT defined in terms of mass

[Anonymous Coward]

Avogadro's number is JUST an artifact of the definition of the (kilo)gram, not a fundamental constant

Actually, Avogadro's number is defined in terms of the Boltzmann constant and the ideal gas constant. The connection between the two and an experimental method of measuring Avogadro's number from observations of either diffusion or Brownian motion was the subject of Einstein's Ph.D. dissertation in 1905.

Arrrrgh I need new gloves...

[Mynorrrr]

If we change to base 12 does that mean I need to grow an extra finger on each hand. I have enough trouble counting to ten as it is!

There would be no argument

[Anonymous Coward]

For it is mathematically provable that 0.111111 (repeating) * 9, does equal 1.

To wit:

1) 0.1111111 * 9 = 1

2) 0.9999999 = 1

3) 0.9999999 * 10 = 1 * 10

4) 9.9999999 = 10

5) 9.9999999 - 0.9999999 = 10 - 1

6) 9 = 9

7) 9/9 = 9/9

8) 1 = 1

And, because I'm anal about some things, I'll officially note that all decimals fractions above are repeating; Else I would've cheated.

Re:There would be no argument

[Anonymous Coward]

5) 9.9999999 - 0.9999999 = 10 - 1

This wouldn't convince myself.

The weight of a kilo

[os2fan]

For all practical purposes, a kilo is defined as 35.274 oz, roughly.

More exactly, the latest definition of the kilogram is "2 lb, 4 oz, 3 dwt, 7 mites 4 periots, 4 1/2 blanks, troy measure."

That's strange . . .

[evgen88]

I thought a kilogram was the weight of a litre of water at a certain temperature. I was also taught that we are mistaken when we use the term kilogram for items we have weighed, as it is a term for mass, we should use newtons. How this works out is that one kilogram weighs one newton in earth gravity. I'm sure someone will point out the fallacy of my recollections.

Yeah, but...

[Grendel Drago]

... the page itself says that nybble is an acceptable alternate spelling. (And since when do links not have the domain name tagged to the end of them? That's weird. Must be that wikipedia.org is 'trusted'. Or something.)

--grendel drago

Isnt it....

[mickq]

I thought it was the weight of 1000 cubic cm of pure water? 1cc of water = 1 gram. 1000 grams = 1kg.

The physical kg block sitting in a vacuum in France is just a solid weight that was accurately set to that weight....isnt it??!

Or did they just pick up a hunk of stuff somewhere and say "Yes, lets call this a kilogram and base our whole weight measurement system off it"???

(Then again, you never quite know with the French....)

Degrees in circle

[j_heisenberg]

That was an interesting question... and the answer goes to:

Babylonians used base 60

Apparently they took the hexagon and observed that the perimeter is exactly 6 times the radius, so 6*60.

I agree

[Pan T. Hose]

One of the nice things about the British system of measurement (which pretty nearly only the Americans use officially, though with a few changes) is that the units are exactly the sort of thing you often want about one of. A pint of beer, a gallon of kerosene, a bale of hay, a pint of milk ...

Not only that. For example, when I want to buy a pair of shoes and the merchant asks me about their size, I say: 1' each. How many centimetres would it be? I have no idea.

Base 60 time

[SeanDuggan]

Admittedly, timekeeping is an artifact of Sumerian influences and their base 60 counting. But honestly, it's not such a bad thing as it means that a minute or an hour is even divisible by 1, 2, 3, 4, 5, and 6. For something like time (Or, for that matter, arc measurements), that division is important. I kind of feel the same way about 12 inches in a foot. It's convenient. And honestly, is multiplying by 60 really that difficult? Now admittedly, it gets slightly more messy dividing.

Technicalities of mass measurement

[SeanDuggan]

Lucky you, you've got a bona-fide metrologist replying. Admittedly one who specializes in automated calibration of electronic instruments, but we get the basic lectures on dimensional analysis too.

The main reason for platinum-iridium is that it's got a very low thermal expansion coefficient. Basically, it doesn't expand or contract much with change of temperature. However, densisty is also important. Don't ever ask a metrologist that old chestnut about which is heavier, a kilogram of lead or a kilogram of feathers, unless you're willing to sit through a few hours of lecture on buoyancy. Yup, it's not just for water and hot air balloons. A denser object of the same mass will weigh slightly less (assuming uniform shape and all that), as it will be slightly less bouyant in the air.

As for your comment regarding a smaller object being less accurate due to relative scale of dust, a smaller mass is also slightly less prone to the influence of the variability of the gravity constant across the Earth's surface. *wry grin* There are a lot of factors you have to deal with when you start working on the scales we do here. And that's not even getting into the gage blocks (length measurement) which have surfaces so smooth that they form a vacuum when touched together, and will spot weld to each other if left overnight...

Re:Technicalities of mass measurement

[Zeal17]

Don't ever ask a metrologist that old chestnut about which is heavier, a kilogram of lead or a kilogram of feathers, unless you're willing to sit through a few hours of lecture on buoyancy.

Well, the way I always heard it (growing up in America) was a pound of lead and a pound of feathers. Which would be accurate even taking buoyancy into effect.

Re:Technicalities of mass measurement

[seminumerical]

Just to clarify, a kilogram (mass) of lead will weigh (force) slightly more than a kilogram of aluminum, because the aluminum displaces more air and is therefore more buoyant? Is that right? or is it the other way around?

Re:Technicalities of mass measurement

[seminumerical]

True, true. Funnily enough the mass/weight distinction causes ordinary people so much trouble that in law courts they sometimes explicity refer to a mass pound. I think they have a name for it (legal pound?) but I am not sure.

I guess in ordinary parlance 100 pounds of potatoes is a scalar, an amount of mass, and not the vector force associated with it.

Er... not really

[SeanDuggan]

It's actually being changed, which is the news.
This is a group of scientists talking about some of the possibilities, who haven't even submitted their idea, let alone had it approved. I honestly expect M. Kilo will be around for another decade or so.

Re:Er... not really

[spdt]

Sure, change, especially one this major, will take some time. "talking about some of the possibilities" is part of the change. Chill, Yo.

"Quantity of light?"

[richyoung]

Am I the only one who has trouble understanding how a "quantity of light" can be used to define the exact value of a kilogram? I mean, I know my radiometer spins when light hits it, but getting from there to defining the kilogram as a quantity of light makes my head hurt a little. Can somebody explain, please?

Quantity of Heavy

[Anonymous Coward]

I think there's an error in the post -- instead of "quantity of light" it should read "quantity of heavy".

Umm, backwards?

[marcus]

A denser object of the same mass will weigh slightly less (assuming uniform shape and all that), as it will be slightly less bouyant in the air

You do mean weigh more because it is less bouyant don't you?

You're absolutely right.

[SeanDuggan]

(n/t)

Re:Anyone Else?

[stanmann]

Because if the gram was defined as a usefully sized object aka kilogram, then the Kilogram would be ~= 1 tonne. which would lead to confusion.

Please think of the drug dealers

[Some_Llama]

now they have to replace all of their current scales and distribution models since kilos will be getting larger or smaller...

Buoyancy, Mass, and Weight

[SeanDuggan]

Correct. I misstated it the first time.

Re:Anyone Else?

[Phisbut]

That is, I'm not asking why they didn't create a standard gram mass, rather why does the SI unit of mass, alone amongst all such units, have a prefix?

Grams existed way before they standardized the mass unit, but it was only an approximation back then. When they standardized it, they made it so the starndard unit for mass would be the mass of exactly one liter of pure water (the liter was already the standard unit for liquid volume). Since the actual mass of a liter of water was much much closer to one thousand grams, they made the kilogram the standard unit for mass. If they had made the gram the standard unit, then it would have been the mass of a milliliter, which is not the official volume unit. Some sort of chicken or the egg situation here...

English unit of mass

[SeanDuggan]

Late follow-up I know, but the standard English unit for mass would be the slug, equivalent to about 14.59 kg or 32.17 lb.