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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."
They set it to 1000 grams.
...if the change it, what would happen if they would auction off the cylinder on eBay?
I'm going to finally lose some weight?
The Answer
1 litre of H2O at ATP?
The next thing you know they will be trying to get the US to switch from imperial units to the metric system....
http://jayceecorder.blogspot.com
I'm going back to pounds and stones.
Pi is exactly equal to 3!
You might find some additional background information about this effort in an earlier Slashdot article about this topic, posted in May 2003.
Replacing the second while your at it, and the meter! Units based off of the earth.
So I guess this means that my suggestion to have the kilogram redefined as (my body mass/90) has been rejected?
http://alternatives.rzero.com/
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.
the 'meter' isn't a unit. perhaps you're thinking of 'metre'?
Please, don't tell us that it'll become 1024 grams!
The SI unit of mass is the kilogram, not the gram.
c = 299,792,458 m/s
This
It's true that it was once defined that way, however, it has been redefined.
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.
I'm a big tall mofo.
Planck's constant would be a very elegant solution - it being the smallest possible quantity of energy, and of course, energy == mass * c^2
Gamers Europe - Gaming News. Reviews.
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.
Picture of the International prototype kilogram:
y pe.jpg
http://www1.bipm.org/utils/common/img/mass/protot
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.
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.
Thus, the meter is not defined by a physical artifact.
Which surprised me, too, when I first learned it.. Is that just because the kilogram finds more use?
Twenties Retirement
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.
I hope I didn't brain my damage.
That would work fine, and I believe was the original definition. Unfortunately, pressure has a mass component, so your definition is circular.
Defining the kilogram DOES define the gram.
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!
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.
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. . . .
When things get complex, multiply by the complex conjugate.
Of course I hadn't RTFA article yet, so what I just said above is idiotic...
Just in case people care, here are the 7 base units:
... or something.
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"
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.
- Jax
Could someone please explain to me "a quantity of light" having mass?
I am honestly confused. (and ignorant)
I dub thee... Sir Phobos, Knight of Mars, Beater of Ass.
In summary, the kilogram is the basic metric unit of weight, not the gram. The gram will be defined by the kg standard.
What I'm listening to now on Pandora...
The pressure part really kills using water as a definition, because it has a mass component. Circular definitions are a no-no.
"My car gets forty rods to the hogshead, and that's the way I likes it!"
;-)
A little offtopic but still revelant
Hold up, wait a minute, let me put some pimpin in it
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?
The pound (mass) is defined as a certain number of kilograms. Just like the inch is defined as a certain number of centimeters.
I can rest at night, not thinking about plum-sized cylinders of platinum-iridium alloy.
Slashdot's first reaction to VMware
..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.
You forgot the CmdrTaco, the basic unit of redundancy.
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.
You'd lose mass instead.
"[Regarding the 'cloud,'] ownership was what made America different than Russia." -- Woz
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.
Why slashdot? Why not?
Did you actually read that web page? It says the meter is defined as the distance light travels in a certain amount of time.
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?
Steal the artifact they use to measure the kilogram right now. That way they'll have to change!!!!
There is no precise definition for a litre of water.
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).
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.
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"?
I think we can keep recursing like this until someone returns 1
What happens when the speed of light changes?.
The definition is a kilogram because the abovementioned lump of metal is one kilogram. A redefinition may ofcourse change this.
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.
wake up and hold your nose
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 :)
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?
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.
The metre was once defined from a physical artifact, but it is now defined in terms of light.
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...
To iterate is human; to recurse, divine!
This is a dupe!
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!"
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.
How the hell is parent Off-Topic? Is everything other than lame-ass, non-funny jokes Off-Topic?
F = m a
(N = kg m s^-2)
Force is nothing but mass * distance / time^2. 1 Newton = 1 kg*m/s^2
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.
- Jax
I think you mean 'things that formerly massed one kilogram would continue to do so'. (Barring any relativitistic changes in mass, of course.)
If corporations are people, aren't stockholders guilty of slavery?
From the Wikipedia article on "kilogram":
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.
To make laws that man cannot, and will not obey, serves to bring all law into contempt.
--E.C. Stanton
... 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...
"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.
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:
The limit of this recursion kg[n] as n tends toward +oo would be the kilogram.
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.
Save the bandwidth. Don't use sigs!
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...
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).
Always going forward, 'cause we can't find reverse.
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
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).
#hostfile 0.0.0.0 primidi.com 0.0.0.0 www.primidi.com 0.0.0.0 radio.weblogs.com
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.
Always going forward, 'cause we can't find reverse.
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.
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.
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.
Giving IE users a taste of their own medicine since 2005 - http://pods.-is-a-geek.net/
"My car gets fourty rods to the hogs head and that's the way I likes it!"
...Had this been an actual emergency, we would have fled in terror, and you would not have been informed.
Pounds measure weight, my friend. As in the effect of a gravitational field on a certain mass.
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.
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
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.
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.
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.
"Secrecy is the keystone of all tyranny. Not force, but secrecy
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.
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.
Gravity, regardless of strength, has no affect on mass. (At least until gravity becomes strong enough create singularities.)
Always going forward, 'cause we can't find reverse.
I kind of like a standard unit of measurment I can hold in my hand or see with my own eyes.
Web hosting that doesn't suck!Dreamhost
African atoms or European atoms?
C|N>K
Thanks.
Always going forward, 'cause we can't find reverse.
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.
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.
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.
Hah! Dragging their feet! Get it?
and since it has a molecular mass of 303.36u you need about 1985791266331147374307356 molecules of that to get to 1 kg
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?
It's official. Most of you are morons.
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.
> 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.
Do it now!
Do it hard!
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.
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.
http://alternatives.rzero.com/
Any technology distinguishable from magic is insufficiently advanced.
At BASF we don't make the kilogram, we make the kilogram better.
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.
If you disagree, post your argument. (-1, Overrated) isn't your personal censorship tool for views you don't like.
Looks like we lost a mu in there somewhere: the resolutions for the popular machines were around 1-10 micrometres.
If you disagree, post your argument. (-1, Overrated) isn't your personal censorship tool for views you don't like.
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.
Wow, sent an e-mail as suggested when clicking on "use classic" banner, and got a fast response that addressed my msg
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.
Or you could do 1867. dm^3 C-12 at STP (101.3 kilopascals, 273 Kelvins).
How many Avogadroes are in guaca-mole?
I guess 6.02x10^23...
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?
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 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?
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.
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...
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
Any sufficiently advanced influence is indistinguishable from control.
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.
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.
Absolute statements are never true
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.
I can return my ancient reagents that are sold in bottles containing "one mole" since the mole changed?
Because the alternative is to use something the french came up with...
Still, the intuitiveness of it is nice.
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
Now we only how to find some magic to compare to...
Analogies don't equal equalities, they are merely somewhat analogous.
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.
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.
-
- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
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
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.
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.
Fly me to the moon Let me sing among those stars Let me see what spring is like On jupiter and mars
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.
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.
Isnt the International standards organization located in France?
This is just a runner up to 'freedom fries.'
___
It's the end of my comment as I know it and I feel fine.
... is defined as being 25.4 millimetres as I recall.
Bitter and proud of it.
"Official definition of the meter"
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
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").
The Raven
Use a balance instead of a scale.
I thionk that they have scales that jiggle things and determine mass from inertia too.
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?
"I have never let my schooling interfere with my education." - Mark Twain
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.
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.
Losing "mass" ... may have to look into that viagra spam, etc...
(too funny to pass up)
Michael J. Ryan - tracker1.info
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!
i speak for myself and those who like what i say.
How many photons does it take to mass one kilogram? I'd imagine roughly a metric fuckton.
With spending like this, exactly what are "conservatives" conserving?
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.
..... 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.
Not to nitpick, but I've heard of a half byte referred to as a nibble.
You mean nybble , don't you?
--grendel drago
Laws do not persuade just because they threaten. --Seneca
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.
Eh?
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...
Said by Arthur C. Clarke
Assembling etherkillers for fun an profit
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.
Drunkeness is an electron free version of virtual reality.
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.
Drunkeness is an electron free version of virtual reality.
What gets lighter but wieghs the same?
:p
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
"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.) "
A blog I run for the wealth
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?
It's official. Most of you are morons.
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.
Avantslash: low-bandwidth mobile slashdot.
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 releaser omnist_re def_kilogram.htm
l ery/kilogra m.htm
http://www.nist.gov/public_affairs/newsf
Personally, I prefer NIST's prior stance, an electronic kilogram:
http://www.nist.gov/public_affairs/gal
Were that I say, pancakes?
Do you realise that the definitions of Fl Oz, Pints and Gallons are different in America and Britain?
.568 of a litre, whereas the American one is 0.473 (so the definition of a gallon is different).
A British Pint is
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.
Jumpstart the tartan drive.
Death penalty?
Incarcerating people without trial?
Extrajudicial killings?
Dunow, it is eluding me....
IANAL but write like a drunk one.
Is for the Avacado number. ;)
Geek2: Whatcha doin', man?
Geek1: Um, I'm about done recalibrating this universal standard kilogram. Just got a... um... er... shit. One. Two. Three...
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...
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.
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 :-)
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).
The creatures outside looked from Alt-Right to Antifa; but already it was impossible to say which was which.
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!
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."
OS/2 - because choice is a terrible thing to waste.
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.
... 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
Laws do not persuade just because they threaten. --Seneca
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....)
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.
It's not: It's based on the second. 1 meter = 1/299792458 seconds
Who ordered that?
Shorly yoo meen "Or wil yoo tri tu justifie speling it nuthing like it sownds"
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.
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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...
This sig has absolutely no significance and serves only to take up screen space and waste the time of the reader.
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.
This sig has absolutely no significance and serves only to take up screen space and waste the time of the reader.
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?
6. Audible Alarm (not shown)
-from a Cuisinart product owner's manual.
You do mean weigh more because it is less bouyant don't you?
Good judgement comes from experience, and experience comes from bad judgement.
- W. Wriston, former Citibank CEO
(n/t)
This sig has absolutely no significance and serves only to take up screen space and waste the time of the reader.
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.
Food not Bombs is a nice platitude but it breaks down when you notice that the Bombees are usually well fed
now they have to replace all of their current scales and distribution models since kilos will be getting larger or smaller...
Correct. I misstated it the first time.
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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...
After 3 days without programming, life becomes meaningless
- The Tao of Programming
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.
This sig has absolutely no significance and serves only to take up screen space and waste the time of the reader.