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fluctuating weight of KG? by noh8rz10 · 2014-01-14 05:55 · Score: 1

why would the weight of the platinum/iridium slug fluctuate? I could imagine the size fluctuating, but not the weight.

Re:fluctuating weight of KG? by Chris+Mattern · 2014-01-14 05:59 · Score: 5, Informative

why would the weight of the platinum/iridium slug fluctuate?
Because a few atoms of the slug can sublimate into the surrounding atmosphere, even at room temperature. And because a few atoms of the surrounding atmosphere can adhere to the slug. And yes, at the precision we're talking about here, it makes a difference.
Re:fluctuating weight of KG? by forrestt · 2014-01-14 06:00 · Score: 1

I can only imagine it fluctuating as a result of corrosion. For example, if it were iron the act of rusting would alter the weight.
Re:fluctuating weight of KG? by firex726 · 2014-01-14 06:06 · Score: 2

Wear... Even at a microscopic level the it can still suffer wear as a result of otherwise imperceptible movement and is also why it's designed as it is.
Since one of the most common SI units is based on however much this thing weights it's important that it be left as intact as possible.
http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_prototype_kilogram
> K4 was originally delivered with an official mass of 1 kg75 g in 1889, but as of 1989 was officially calibrated at 1 kg106 g and ten years later was 1 kg116 g. Over a period of 110 years, K4 lost 41 g relative to the IPK.
Re:fluctuating weight of KG? by gstoddart · 2014-01-14 06:11 · Score: 1

Mostly I think it's dirt and other crud.
Essentially, the reference object isn't free from contamination or interacting with its environment.
We don't have a mechanism which allows us to define it in a more rigorous manner which can be reproduced, so we've got this hunk of of whatever it is sitting on a shelf which is defined as the reference kilogram. (OK, it's not just sitting on a shelf, but close)
Not what you'd call an objective standard. More of an approximation which is official and which the other official approximations are measured against.
Unlike an atomic clock where you can precisely define the unit of time in wavelengths of whatevers, there's no way to define the kilogram in a more specific way.

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Re:fluctuating weight of KG? by Anonymous Coward · 2014-01-14 06:12 · Score: 2, Interesting

That's part of the problem. Scientists aren't exactly sure. Shortly after it was made, several copies were made in 1889 that were verified to be the exact same mass. Over the years, the mass of the original and its copies have slightly drifted. The copies appear to have grown heavier, while the original has grown lighter. But even that's hard to determine for sure, since we can only be sure of the *difference* of the masses, not their absolute mass, because absolute mass is defined in terms of these kilogram masses in the first place.
It's theorized that air molecules may be attaching to the copies (they are also kept in a vacuum environment, but no vacuum is perfect), but if that's the case, why hasn't it happened to the original? The difference is only 50 ug, but that comes out to be 0.005%, which is huge for scientific applications. All of this means that they need a better quantitative standard for the kilogram.
Re:fluctuating weight of KG? by Minwee · 2014-01-14 06:36 · Score: 2, Insightful

Fucking genius! If only it were iron it would be corroding, but it's platinum and irridium. Corrosion is not a big factor. Forgetting to dust it would alter the mass more.
Actually, remembering to dust it is what causes its mass to change. The problem of how to properly clean the things has been going on for years.
Re:fluctuating weight of KG? by Muad'Dave · 2014-01-14 06:43 · Score: 2

K4 was originally delivered with an official mass of 1 kg75ug in 1889, but as of 1989 was officially calibrated at 1 kg106ug and ten years later was 1 kg116ug. Over a period of 110 years, K4 lost 41ug relative to the IPK.
Your mu's got eaten by slashdot. Those should all be micrograms. Naturally μ doesn't work.

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Re:fluctuating weight of KG? by msauve · 2014-01-14 06:50 · Score: 1

s/ g / microgram /

Preview is your friend, /. doesn't support Unicode.

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Re:fluctuating weight of KG? by Daniel+Hoffmann · 2014-01-14 07:22 · Score: 1

Huh, I thought it was because some sub-nuclear reaction involving background-radiation of some kind hitting the slug. I would assume they leave the slug in an almost vacuum container.
Can someone confirm if that is indeed the case?
Re:fluctuating weight of KG? by AvitarX · 2014-01-14 07:25 · Score: 1

Wouldn't a vacuum accelerate the sublimation part of the description?
I actually thought it was losing weight, I didn't know it was gaining it too.

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Re:fluctuating weight of KG? by rahvin112 · 2014-01-14 07:25 · Score: 1

Platinum and Iridium sublimate? Are you serious? The reason they choose platinum is because of it's durability. When you scratch platinum you don't lose material, you just create a furrow in the metal and all the mass is retained. Iridium I believe is the same, and it's a platinum slug with an Iridium coating.
Now collecting a few atoms of air I can see happening, but maybe that's what the Iridium coating is for. Or maybe that is why they store the slug in a temperature controlled vault, IIRC either in a low pressure or an inert gas (I can't recall which it was or if it was both).
Re:fluctuating weight of KG? by Immerman · 2014-01-14 07:44 · Score: 2

>Unlike an atomic clock where you can precisely define the unit of time in wavelengths of whatevers, there's no way to define the kilogram in a more specific way.
Really? Seems to me it would be easy enough to say 1g = 1/12 the mass of one mole of Carbon-12, or your element of choice - preferably something common, stable, and monoisotopic for convenience (http://en.wikipedia.org/wiki/Monoisotopic_element). Obviously we'll want to choose our atom carefully since per-nucleon mass is different fro every element. Maybe iron since it has the minimum per-nucleon energy, meaning all other nucleons will have a mass slightly >1, or perhaps hydrogen-1 as the most abundant element, and the closest we can get to the mass of a free proton. Of course that doesn't really scale all that well for practical applications, nobody is actually going to want to count out the 602,214,130,000,000,000 atoms necessary to get to even the microgram range using modern technology, but there's no reason we couldn't define the unit in such terms, and then continue using carefully protected metal slugs as "best approximation" reference masses. Heck, perhaps we could even use a low-speed particle accelerator to embed a precise number of atoms into a reference mass to create a specific mass-delta.

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Re:fluctuating weight of KG? by fisted · 2014-01-14 07:57 · Score: 1

duh, you'd think they could just put it on the calibration scale and leave it there. no need to manipulate it anymore, then.

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Re:fluctuating weight of KG? by FatdogHaiku · 2014-01-14 08:11 · Score: 5, Informative

It is kept in air, but under bell jars. Way more than you ever wanted to know here...
http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_prototype_kilogram

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Re:fluctuating weight of KG? by justthinkit · 2014-01-14 08:38 · Score: 1

When you scratch platinum you don't lose material

Citation?

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Re:fluctuating weight of KG? by tibit · 2014-01-14 08:44 · Score: 1

That it varies as a whole is of no consequence. What matters is the differential variations in weight. Something as simple as lubricant outgassing will affect the results a whole lot - remember that they have the kilogram's uncertainty down to a couple dozen ppb IIRC. Basically, such a scale has to be zeroed before each weighing, and to do that you need to lift the weight off of it.

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Re:fluctuating weight of KG? by tibit · 2014-01-14 08:45 · Score: 1

Not 0.005%, but rather 0.000'005%.

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Re:fluctuating weight of KG? by Electricity+Likes+Me · 2014-01-14 08:52 · Score: 2

It's not iridium coated, it's iridium-alloyed - adds hardness.
The problem here is declaring something involving atoms impossible, and well, on the atomic scale nothing is. It sits in lit room at room temperature - there is a whole hell of a lot of EM falling on it, and so every now and again somewhere on it you might exceed the work function of the metal and sputter it. You've also got to deal with not just air sticking to it, but being absorbed into it's bulk - atmospheric humidity would be a big concern since water sticks to everything and is just about impossible to get rid of. Then you've got hydrogen and helium diffusion as well.
Re:fluctuating weight of KG? by sjames · 2014-01-14 09:26 · Score: 2

That's great in theory, but in practice, there is a master kilogram and several reference kilograms actually used for standardizing measurement. They keep drifting apart somehow.
That somehow is either the evil machinations of the faery world or it is sublimation and adhesion.
Re:fluctuating weight of KG? by sjames · 2014-01-14 09:42 · Score: 1

How are you going to get the other mass onto the balance without disturbing anything?
Re:fluctuating weight of KG? by kimvette · 2014-01-14 10:16 · Score: 1

http://en.wikipedia.org/wiki/Vapor_pressure

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Re:fluctuating weight of KG? by fisted · 2014-01-14 11:01 · Score: 1

It would at least get rid of the loss of material caused by picking it up and putting it somewhere, then later putting it back, by whatever means.
That being said, my comment was semi tongue-in-cheek

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Re:fluctuating weight of KG? by forrestt · 2014-01-14 12:11 · Score: 1

While platinum and iridium (or irridium if we want to go with your spelling) are more corrosion-resistant than iron, they are not corrosion-proof. "Not a big factor" is fine for short periods of time. The hundreds of years this thing is expected to exist and the extreme precision that it is supposed to remain accurate to are enough to make "not a big factor" a "big enough factor" to worry about. If not, it would have been made out of whatever it is your brain is made out of. That appears to lose mass quite quickly.
Re:fluctuating weight of KG? by Rich0 · 2014-01-14 15:13 · Score: 3, Funny

Platinum and Iridium sublimate? Are you serious?
Sure it can. It just does it VERY slowly. The solid state is greatly preferred for these metals at room temperature, but at any temperature and pressure solid, liquid, and gas are all in equilibrium. When you're talking about thermodynamics and statistical mechanics, about the only absolute is zero, and that is a state that doesn't physically exist anywhere.
Then throw in quantum mechanics. There is probably some small but finite probability that I'll appear in your living room before I finish typ
Re:fluctuating weight of KG? by submain · 2014-01-14 15:46 · Score: 3, Funny

Almost sounds like something coming from Douglas Adams. From the wikipedia article:

The magnitude of many of the units comprising the SI system of measurement, including most of those used in the measurement of electricity and light, are highly dependent upon the stability of a 135-year-old, golf ball-size cylinder of metal stored in a vault in France.
Re:fluctuating weight of KG? by Electricity+Likes+Me · 2014-01-14 18:57 · Score: 1

There are proposals to build reference standards like this, but how you define it is irrelevant if you can't actually measure it that way accurately. One proposal for the kilogram standard was based on electrochemical deposition of gold (ion acculumation). This is appealing because you can as this article shows, count electrons very accurately (and we get better at it all the time) and so if you're pulling Au+ out of solution, then you just do so until you reach the exact number of electrons you needed to get the exact amount of Au you needed. More importantly, you can do it fast.
Unfortunately, it doesn't work - the practical realizations are still less accurate then the current system, and it also requires fixing a whole bunch of other constants, and it also is very difficult to actually create secondary standards off of the mechanism.
Re: fluctuating weight of KG? by Anonymous Coward · 2014-01-14 21:50 · Score: 1

Imagine the havoc terrorists could wreak if they blew up that building, or stole and melted the reference slug.
Re:fluctuating weight of KG? by Rich0 · 2014-01-15 02:31 · Score: 2

In classical statistical mechanics, you can have a solid that has a low enough, but non-zero temperature such that the change of any given atom having enough energy to leave the surface has effectively zero probability on a relevant timescale.
That "effectively zero probability" means that it sublimes. It just does it REALLY slowly. And that is if you want to keep the standard at a near-absolute-zero temperatures for decades. That creates a whole different set of problems. Can you weigh it as accurately at those temperatures? If you have to warm and cool it, does the mass change due to damage during expansion/etc? Can you maintain it at that temperature without any contamination (if it is that cold than any molecule of gas that leaks in will condense or solidify).
That's the whole problem with the kilogram standard. They're probably managing it as best as they can already, but it will never be perfect, and they're well past the point of diminishing returns so anytime you want to consider any improvement you have to factor in all of physics.
Re:fluctuating weight of KG? by Rich0 · 2014-01-16 06:28 · Score: 1

No, the key word is effective, as in you scale it to the needs of the system. You can adjust what is "cold enough" such that the probability of it subliming on the time scale of centuries is zero. It will still sublime on some longer timescale. You can work out that classically, around 7 K there would be is likely not a single atom in the whole kilogram prototype with enough energy to escape the surface.
So, which is it? "Zero" probability, or "likely" not a single atom. They are NOT the same thing. You can lower the sublimation rate to an arbitrarily low level via classical physics, but you can never make it zero.
Re:fluctuating weight of KG? by Rich0 · 2014-01-17 03:23 · Score: 1

If the entire body has less energy than the energy needed to break whatever type of bond is holding its atoms together, there is zero probability in classical physics of any atom breaking free, as even in the unlikely scenario that the energy of the entire system ended up in one atom, it wouldn't be enough. This would still be above absolute zero.
I'll agree with you on that one. Of course, that is still limited to classical mechanics, and storing the kg prototype at fraction of a degree above absolute zero has a whole different set of problems, which was my original point.

If you had something like a 1% chance per century of losing an atom, on a time scale of a century your expected sublimation would be zero, although on a time scale of a billion years it would be different.
No, over the period of a century your expected rate of sublimation would be somewhere between zero and the weight of an atom. You can't just turn small numbers into zero simply because they're small. Well, I guess it works if you are into credit default swaps.
In any case, at the temperatures that would make the sublimation rate anywhere near that low there would be a bunch of other practical problems with the maintenance of the kg prototype.
My point was that when you're talking about measurements at the level of precision required just about any effect of physics becomes relevant. Ok, so you drop the temperature to .0000001K. Then in the year 20,000 after you've finished cooling it down enough, then how do you weigh it without warming it back up or having the temperature cause other problems? Oh, and how do you keep random molecules of gas from diffusing into your storage vessel and instantly condensing onto the surface (and warming it up considerably in the process)?

Arbitrariness by Anonymous Coward · 2014-01-14 05:58 · Score: 1

Unless we're willing to dump our current units, the new definition will be some arbitrary-seeming number chosen to be consistent with a fairly precise version of what we're already using.

Re:Arbitrariness by Chris+Mattern · 2014-01-14 06:03 · Score: 1

Correct. But by tying it to an electron charge, it becomes well-defined and highly accurate, even if it does have to depend on an arbitrary number. That will be an distinct improvement to those depending on extreme precision, even though the average joe with a multimeter in his hand won't see any difference (and won't even need a new multimeter).
Re:Arbitrariness by lgw · 2014-01-14 11:01 · Score: 1

I thought an Amp was a Coulomb/s and the Coulomb was just a standardized, exact count of electrons. Shows what I know. At least now, we could do it that way.

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Re:Arbitrariness by Giant+Electronic+Bra · 2014-01-14 15:55 · Score: 1

Yeah, that's the definition I always knew, a Coulomb is one Avagadro's Number of fundamental charges. The problem is that's a great theoretical definition, but actually measuring out 6.022x10^23 electrons is a bit difficult... As someone pointed out earlier in the thread, the error in the known value of NA is about 1 part in 30 billion, which is not bad, but not good enough either. There are some other ways to measure an Amp of course, but they all get complicated rather quickly because you have to know at least 2 other values very precisely.

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Re:Arbitrariness by Anonymous Coward · 2014-01-14 17:12 · Score: 1

A Coulomb is about 6.24e18 fundamental charges, not related to Avogadro's number. If it was just a mole, then the mole or Ampere could possibly be considered derived units of the other.
Re:Arbitrariness by lgw · 2014-01-14 19:19 · Score: 1

I get that confused too, the mantissa being close and all. What's a few orders of magnitude between friends.

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Condescend much? by Oligonicella · 2014-01-14 05:58 · Score: 2, Interesting

"almost as much of an embarrassment"

You would have done better with the technologies at hand at the time how?

Re:Condescend much? by kry73n · 2014-01-14 06:03 · Score: 1

You would have done better with the technologies at hand at the time how?
Can we do better with the technologies at hand right now?
Re:Condescend much? by girlintraining · 2014-01-14 06:21 · Score: 1

You would have done better with the technologies at hand at the time how?
You would have practiced science using methodologies nearly a century out of date when? See that's the thing about science -- it's supposed to change in response to new data. And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.

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Re:Condescend much? by Anonymous Coward · 2014-01-14 06:29 · Score: 1

There is nothing wrong with our units of measurement. They can be anything we want them to be. The point is that we want a unit that can be independently recreated anywhere by anyone and not a magic piece of precious metal that we measure.
Re:Condescend much? by Phreakiture · 2014-01-14 06:41 · Score: 1

Can we do better with the technologies at hand right now?
Um . . . didn't we just do that? Isn't that what the article is about?

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Re:Condescend much? by AthanasiusKircher · 2014-01-14 06:53 · Score: 1

And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.
Umm, I'm pretty sure scientists have been working on the kilogram problem for some time. Your use of "stubbornly" implies that there's some sort of resistance to a redefinition. But I don't think there's any evidence that that's the case.
Here's a NYT article from 2003 detailing the then-current attempts at redefinition. I'm sure there are older things out there detailing the scientific efforts to work on this problem, too... this was literally one of the top three hits in an internet search.
Anyhow, in 2005, the International Committee for Weights and Measures formally recommended a redefinition. In 2011, the General Conference on Weights and Measures agreed. If you want to see all the proposed revisions, they are nicely summarized in a Wikipedia article here.
It may be somewhat true that the kilogram redefinition lagged a bit behind other units, mostly because the other units had practical applications where the need for increased precision was rising more rapidly. But given that the attempts to provide a standard measurement system are ongoing, and the proposed redefinitions make use of technology that is still being refined to maintain a high-enough level of accuracy to supersede the old standard, there's no reason to call this an "embarrassment" "stubbornly stuck in the past."
Scientists are actively working on the problem -- and have been for quite some time.
Re:Condescend much? by Baloroth · 2014-01-14 06:57 · Score: 1

You would have done better with the technologies at hand at the time how?
You would have practiced science using methodologies nearly a century out of date when? See that's the thing about science -- it's supposed to change in response to new data. And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.
You have a better idea for a mass unit? The scientific community would absolutely love to hear about it, because every other idea either doesn't work at all, or isn't practically measurable (sure, you could define it as x number of atoms of y substance, but good luck counting out a few trillion atoms with precision every time you want to make an accurate measurement).
Most of the basic units of measurement in science have in fact been redefined when someone came up with a better system. Mass, however, it turns out, is really bloody hard to do better. I wouldn't call it "embarrassing" when the laws of physics prevent you from doing any better.

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Re:Condescend much? by blueg3 · 2014-01-14 07:04 · Score: 2

Such as using the American Imperial system of measurement?
Nobody does science using U. S. customary units.
Re:Condescend much? by UnknownSoldier · 2014-01-14 07:23 · Score: 4, Interesting

I'll probably get down modded but it is not just the technologies but the basic definitions of the SI system are pretty fucked up.
There are numerous problems, the primary being:
* the seven SI base units are not independent
e.g. the Amp depends on the definition of the kilogram ?!?!
http://www1.bipm.org/en/si/si_constants.html#figure
Quoting Dr. Xavier with my emphasis added:
"If for instance, one had to change the definition of the Kg unit, we see that the fundamental units candela, mole, Amp and Kelvin would change as well. .. So one cannot say there are seven fundamental SI units if these units are not independent of each other. The other big fault is the obvious redundancy of units. Although not very well known to all of us, at least two of the seven base units of the SI system are officially known to be redundant, namely the mole and the candela. These two units have been dragging along, ending up in the SI system for no reason other than historic ones. "
* http://www.blazelabs.com/f-u-suconv.asp
Re:Condescend much? by UnknownSoldier · 2014-01-14 07:54 · Score: 1

You keep using this word "fundamental units". I don't think it means what you think it means. :-)
Speed of Light in a vacuum is a fundamental constant expressed in units of m/s. In this case, space (m), and time (s) are the fundamental units.
The Plank length "is a base unit in the system of Planck units" so yes it can be considered a fundamental unit.
It is interesting to note: "The Planck length can be defined from three fundamental physical constants: the speed of light in a vacuum, Planck's constant, and the gravitational constant."
* http://en.wikipedia.org/wiki/Planck_length
Re:Condescend much? by UnknownSoldier · 2014-01-14 08:24 · Score: 1

Also of interest:
"Redefinition of the kilogram: a decision whose time has come"
http://www.acs.org/content/dam/acsorg/about/governance/committees/nomenclature/meetings/2007-fall-attachment-01a.pdf
Re:Condescend much? by maxwell+demon · 2014-01-14 10:10 · Score: 1

You certainly want to qualify the "by anyone" part ... I doubt e.g. that the next person you meet at the bus station is very likely to be able to build a caesium clock (and thus recreate our time unit).

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Re:Condescend much? by xvan · 2014-01-14 10:25 · Score: 1

You could define Space or time as a function of the speed of light. But you'd have to measure the speed of light really accurately.
Re:Condescend much? by maxwell+demon · 2014-01-14 10:25 · Score: 1

Speed of Light in a vacuum is a fundamental constant expressed in units of m/s.
Speed of light in vacuum is a fundamental constant, but whether you express it in units of m/s, in units of furlongs per fortnight, or in units of the speed of light doesn't matter for its value. And exactly because it is a constant, it makes a perfect unit for speed. Because that's what a unit is: A constant quantity to which other quantities of the same kind are compared. So if you say something is going at half the speed of light, you are using the unit "speed of light", and quantify a certain speed by multiplying that unit with a number (in this case 1/2).

In this case, space (m), and time (s) are the fundamental units.
No, space and time are not units. Meter (m) and second (s) are units of length and time. In the SI system they are fundamental units because they are defined to be. It is easy to define another system of units where other units take the role of the fundamental units. Even units belonging to other physical quantities (such as speed).

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Re:Condescend much? by Rich0 · 2014-01-14 15:33 · Score: 1

There are numerous problems, the primary being:
* the seven SI base units are not independent
e.g. the Amp depends on the definition of the kilogram ?!?!
Well, it is kind of hard to build an apparatus to measure the value of the amp without constructing it out of matter or energy, and matter and energy are both described by other units. The forces of nature are interesting to us because they affect things that we can see and feel, and indeed sight and feeling are themselves the result of the forces of nature. So, there is really no such thing as a pure force that acts independently of anything else and therefore can be defined independently of anything else, unless you want to talk about the supernatural.
Distance would be meaningless without motion, and motion is meaningless without time. Mass is really just a measurement of inertia, and that is meaningless without motion or force. You could look at mass as a measurement of gravity instead, but again that is a force.
So, the relationship between the fundamental units of measure is tied up in the nature of physics.
Also, which units are fundamental is entirely a matter of convenience. You could just as easily make either the Amp or the Coulomb fundamental, or make velocity fundamental and distance derived (indeed, that's basically how the definition works anyway).
The mol is a bit of an interesting unit, because ultimately it is a counting unit. If NA were determined with absolute precision it would basically be dimensionless, like the unit of the "dozen." Certainly a level of tradition is caught up in the SI base units, but it doesn't really make them defective in any way. Whether we have a special unit for the Cd has a lot less impact on physics than whether the mathematicians embrace the axiom of choice. :)
Re:Condescend much? by Your.Master · 2014-01-14 15:47 · Score: 1

Speed of Light in a vacuum is a fundamental constant expressed in units of m/s. In this case, space (m), and time (s) are the fundamental units.
I think you might be interested in looking up the concept of linear independence. It's kind of like being Turing complete. Your system doesn't have to have a fundamental unit for space or time at all, any more than you need one for speed. It's enough to be able to combine other fundamental units to generate a derived unit of space or time.
There is absolutely no reason that the fundamental units can't be c (the fundamental unit of speed) and seconds (the fundamental unit of time), with distance being the derived unit. C makes a wonderful unit precisely because it's a universal constant, and because it makes it really easy to remember how fast the speed of light is (it's 1!). You could even make your fundamental units a velocity unit and an acceleration unit, with both time and space being defined in terms of those.
Re:Condescend much? by Anonymous Coward · 2014-01-15 00:31 · Score: 1

If you did actually have a broad knowledge about the subject, you'd have known how hard it is to define units that span the entire unit volume, have an unambiguous definition, and can be accurately measured.
If you think you can do better, by all means submit your new definitions along with your experiments that show they'll work to Nature. But in the meantime, don't post ‘SI is fucked up’ on Slashdot, especially not without suggestions for improvement, because that leaves an unwarranted impression an solves exactly nothing.
As for the various redundant units, abolishing them doesn't change anything but notation. (As the source you cite acknowledges.)
I would agree that there is room for improvement in SI, but saying it's ‘fucked up’ ignores the hard work done by people who are much more knowledgeable about this subject than you yourself.
Re:Condescend much? by AmiMoJo · 2014-01-15 02:00 · Score: 1

How else would you do it though? If you can't measure natural constants such as say the weight of a particular atom you have to create your own. Making all the measurements related makes conversions and further measurements convenient.
Now that we can define SI units using natural constants the relationships hold down to a few decimal places, which is good enough for many purposes, and we can have extreme accuracy for those who need it. I'm not sure how it could be been done better, given the limitations of the time.

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Re:Condescend much? by Rich0 · 2014-01-15 02:41 · Score: 1

Certainly agree in principle, but the real challenge with the counting approaches is that in many cases they aren't as accurate. Everybody wants to ditch the current kilogram, but it works so well that none of the alternatives are suitable replacements.
Defining both the second and the meter on wavelength/frequency measurements probably still effectively fixes the speed of light, assuming the speed of light really is fixed as everybody believes it is.
The mol is the most obvious case where you can define it by counting, since it really is a counting measure.
Re:Condescend much? by TangoMargarine · 2014-01-15 06:07 · Score: 1

I think metric officially lost its "it just makes more sense! Everything's 10s!" excuse when I found out that a meter is now defined as how far light travels in 1/299,792,458th of a second. And they say *we* use weird numbers!

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Re:Condescend much? by UnknownSoldier · 2014-01-15 06:14 · Score: 1

replace "fucked up" with non-orthogonal
Better?
Re:Condescend much? by UnknownSoldier · 2014-01-16 13:22 · Score: 1

> the concept of linear independence. .. It's enough to be able to combine other fundamental units to generate a derived unit of space or time.
You actually bring up a very interesting point ! Our current understanding and Science treats space and time as being independent. In my studies I have come across other systems that propose that space-time is linked. IIRC Dewey Larson's "Reciprocal System" is one such very interesting approach !
* http://www.reciprocalsystem.com/dbl/
> C makes a wonderful unit precisely because it's a universal constant,
Given our current understanding it certainly seems to be, but I would hesitate to call it a universal constant, when we have explored, what, less then 0.00000001% of the visible universe. More data is required before we can come safely come to that conclusion.

Definition of a kilogram by Infiniti2000 · 2014-01-14 05:59 · Score: 4, Funny

A kilogram is straightforwardly defined as 2.20462 pounds. Simple enough.

Re:Definition of a kilogram by forrestt · 2014-01-14 06:06 · Score: 1, Funny

I guess I missed the humor tag in your original post.
Re:Definition of a kilogram by gman003 · 2014-01-14 06:08 · Score: 2

And as we all know, the pound is defined as 7000 grains, which are simply defined as the mass of a grain of wheat.
Re:Definition of a kilogram by Vanderhoth · 2014-01-14 06:11 · Score: 1

How is the pound defined? Thought I'd look it up , but all I can find is Wikipedia that says a pound is defined as "(b) the pound shall be 0.45359237 kilogram exactly".

The definition for a pound of force was even less helpful as it's related to an Avoirdupois pound, which is defined as:

The avoirdupois pound, also known as the wool pound, first came into general use c. 1300. It was initially equal to 6992 troy grains. The pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth, the avoirdupois pound was redefined as 7,000 troy grains. Since then, the grain has often been an integral part of the avoirdupois system. By 1758, two Elizabethan Exchequer standard weights for the avoirdupois pound existed, and when measured in troy grains they were found to be of 7,002 grains and 6,999 grains.
Re:Definition of a kilogram by trongey · 2014-01-14 06:16 · Score: 5, Funny

I guess I missed the humor tag in your original post.
That's OK. You were publicly correcting someone for the misuse of units of measure.
None of us expected you to have a functional sense of humor.

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Re:Definition of a kilogram by girlintraining · 2014-01-14 06:28 · Score: 1

A kilogram is straightforwardly defined as 2.20462 pounds. Simple enough.
Yeah right! There's over a dozen different definitions for the "pound". You're citing the intuitively named international avoirdupois pound designation. Unfortunately, your own definition is over a century out of date! The Mendenhall Order of 1893 defined it as 2.20462 ... but the following year, someone got their hands on a British kilogram and it was redefined to be 2.20462234.
And where-fore did the previous pound measurement come from, before it was normalized to the kilogram? Why, the weight of 120 Arabic silver dirhams, found in some king's dingy treasury of course! Not to be outdone, the previous definition was based on the average weight of a pile of wheat traded in the town of Troy.
It's all so simple!

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Re:Definition of a kilogram by ubergeek65536 · 2014-01-14 07:46 · Score: 1

Weight changes as gravity changes, mass does not. A kilogram is a measure of mass.
Re:Definition of a kilogram by H0p313ss · 2014-01-14 09:58 · Score: 1

I guess I missed the humor tag in your original post.
That's OK. You were publicly correcting someone for the misuse of units of measure.
None of us expected you to have a functional sense of humor.
Which makes me wonder, is there an internationally accepted standard unit for measuring humor?
If not I would propose the Leacock

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Re:Definition of a kilogram by Sardaukar86 · 2014-01-14 11:49 · Score: 1

Ooohhhh!
So how to do you convert from Dollars, or Euros for that matter?
With a set of balance scales, naturally.

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Re:Definition of a kilogram by forrestt · 2014-01-14 11:58 · Score: 1

You are correct. I should have said mass. I'm sure I would have picked up on it after several more proof reads, but this is Slashdot after all. We aren't expected to read the article, why should we read our own posts?
Re:Definition of a kilogram by forrestt · 2014-01-14 12:15 · Score: 1

Yeah I realized it was supposed to be funny after I responded to it (while it was "Score:0") and saw the "(Score:4, Funny)". I totally understand all the aspects of the humor after rereading it with its intended purpose.
Re:Definition of a kilogram by forrestt · 2014-01-14 12:17 · Score: 1

Thank you. You made me laugh.
Re:Definition of a kilogram by geekoid · 2014-01-14 12:39 · Score: 1

There is! Humor falls of via the inverse sqr law, but for time instead of area.
So every doubling of time it a 1/4 as funny.
The unit of measure this fall off is called the 'Chevy Chase'

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Re:Definition of a kilogram by geekoid · 2014-01-14 12:43 · Score: 1

well done, you shown that standards get more accurate with time. Genius.

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Re:Definition of a kilogram by TangoMargarine · 2014-01-15 06:16 · Score: 1

They're both just numbers somebody pulled out of their ass. The only thing that makes metric objectively better in any way would be if their measurements are more precise. How precise are the U.S. baseline object(s)?

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2×107 newtons per metre of length? by Anonymous Coward · 2014-01-14 06:00 · Score: 1

that's almost 214 newtons per metre of length!

Re: 2×107 newtons per metre of length? by bryanc · 2014-01-14 06:26 · Score: 1

It's 2 × 10–7. (http://en.wikipedia.org/wiki/Ampere)
Re: 2×107 newtons per metre of length? by Waffle+Iron · 2014-01-14 06:40 · Score: 1

So in other words, 13?
Re: 2×107 newtons per metre of length? by Overzeetop · 2014-01-14 06:56 · Score: 2

6, if you regularly read Facebook for math tips.

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Re: 2×107 newtons per metre of length? by mythosaz · 2014-01-14 07:01 · Score: 1

If it makes you feel any better, I enjoyed your PEMDAS joke :)
Re: 2×107 newtons per metre of length? by es330td · 2014-01-14 07:21 · Score: 1

I'm starting to think the most important thing to learn in this particular set of comments is that many people have problems posting special characters and notations to /.
Re: 2×107 newtons per metre of length? by rossdee · 2014-01-14 08:30 · Score: 1

A Newton was a portable computing device from a couple of decades ago. It was made by Apple
Steven Seagal had one in under siege 2
Re: 2×107 newtons per metre of length? by geekoid · 2014-01-14 12:44 · Score: 1

2 x 10-7
2 x -70
140

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Gravity is not constant... by fullmetal55 · 2014-01-14 06:01 · Score: 2, Informative

It's hard to consistantly and accurately measure weight when the force of gravity constantly changes, add to the fact that there may be radioactive decay of trace elements, oxidation of metals, Dust/erosion, sublimation of trace components), it's easy to understand how using a physical object to consistantly measure a weight, would fluxuate. when your "constants" are actually "variables" it's really hard to nail down constants...

Re:Gravity is not constant... by IDtheTarget · 2014-01-14 06:11 · Score: 2

The kilogram is a measure of mass, not weight.
Re:Gravity is not constant... by oodaloop · 2014-01-14 06:26 · Score: 2

No shit. And measuring the mass of the slug in question involves weighing it. Or do you have another method involved for determining the mass of an object used as the constant for measuring mass?

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Re:Gravity is not constant... by Phreakiture · 2014-01-14 06:34 · Score: 2, Informative

Or do you have another method involved for determining the mass of an object used as the constant for measuring mass?
Placing two masses on a balance is the usual method . . . . and it is gravity-independent. Gravity is necessary, of course, but it only needs to be constant across the two platters of the balance.

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Re:Gravity is not constant... by gardyloo · 2014-01-14 06:37 · Score: 1

1) Measure its acceleration when subjected to a known force.
2) Measure the period of a system where it's part of the inertial loading, and the restoring characteristics are known (or can be decoupled post-experiment).
Re:Gravity is not constant... by LordLimecat · 2014-01-14 06:37 · Score: 3

Except now all you have is a ratio of two masses, rather than an absolute quantity. What exactly would you balance the kilogram reference against?
Re:Gravity is not constant... by quenda · 2014-01-14 06:42 · Score: 1

A simple beam-balance scale can measure mass unaffected by gravity variations. You just need a reference mass.
Re:Gravity is not constant... by UnknownSoldier · 2014-01-14 06:43 · Score: 2

The parent's point about gravity being variable really needs to be modded up!
To drive the point home ...
http://en.wikipedia.org/wiki/File:Earth-G-force.png
As you get closer to the earth the force of gravity increases as expected however at the Gutenburg discountinuity the force of gravity then goes down to zero at the core.
Re:Gravity is not constant... by Immerman · 2014-01-14 06:43 · Score: 4, Insightful

Sure, the same way they "weigh" things in freefall - measuring the radial forces necessary to keep it moving in a fixed circular path at a given speed. You can even vary the speed to get multiple measurements to reduce error. That may be as simple as a scale in a centrifuge, but does not depend on any way on potentially fluctuating gravitational field. It also incidentally directly measures inertial mass, rather than gravitational mass, which *apparently* is always present in precisely proportional amounts, but which we currently have no accepted theoretical reason to believe is a fundamental equivalence.

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Re:Gravity is not constant... by djdanlib · 2014-01-14 06:44 · Score: 4, Funny

A duck.
Re:Gravity is not constant... by Minwee · 2014-01-14 06:44 · Score: 1

No shit. And measuring the mass of the slug in question involves weighing it. Or do you have another method involved for determining the mass of an object used as the constant for measuring mass?
Comparing it to another mass using a balance makes any variation in the force of gravity irrelevant. You could travel to Mercury or Jupiter and still make accurate measures of mass using the same scale. Of course, that brings us right back to needing something to compare your mass _to_, and that something is eventually a cylinder made up of platinum and iridium stored in a vault just outside of Paris.
Re:Gravity is not constant... by Phreakiture · 2014-01-14 06:45 · Score: 1

So if it weighs the same as a duck . . .

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Re:Gravity is not constant... by Phreakiture · 2014-01-14 06:47 · Score: 3, Insightful

Except now all you have is a ratio of two masses, rather than an absolute quantity. What exactly would you balance the kilogram reference against?
You would use it to callibrate another mass as being a kilogram. I know this is kind of a circular problem, but that's really why the fluctuating mass is troubling, because that's supposed to be the stable benchmark, and it has proven not to be so stable.

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Re:Gravity is not constant... by oodaloop · 2014-01-14 06:49 · Score: 1

If you're joking, I think that's hysterical. I'm just not sure you're joking.

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Re:Gravity is not constant... by Baloroth · 2014-01-14 06:52 · Score: 1

Except now all you have is a ratio of two masses, rather than an absolute quantity. What exactly would you balance the kilogram reference against?
Unless one of those masses is the reference that you define as the kilogram, in which case you have the "absolute" mass. All masses are defined in terms of some ratio to a fixed reference mass. It's not a terribly good system, but if you have a better one that actually works, the scientists would love to hear about it.

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Re:Gravity is not constant... by es330td · 2014-01-14 07:16 · Score: 2

Then you can build a bridge out of it.
Re:Gravity is not constant... by tepples · 2014-01-14 07:19 · Score: 1

First define a known force. Right now the unit of force is defined in terms of a kilogram.
Re:Gravity is not constant... by Nemyst · 2014-01-14 07:19 · Score: 1

That's the point that was being made here, though. The kilogram is defined in relation to this cylinder, which happens to change mass, so the definition of the kilogram also changes, which is less than ideal. I doubt the GP was suggesting a solution, merely explaining the problem.
Re:Gravity is not constant... by zerro · 2014-01-14 07:37 · Score: 1

Thank you, for devolving this into a Monty Python joke!
+1
Re:Gravity is not constant... by stdarg · 2014-01-14 07:40 · Score: 3, Insightful

What's wrong with fixing Avogadro's number at something like 6.022 * 10^23 instead of defining it as the number of atoms of blah in blah, then saying a kilogram is 1/12 of the mass of Avogadro's number of Carbon 12 atoms. I'm sure that's been floated.. is the problem the arbitrariness of the number?
Re:Gravity is not constant... by hchaos · 2014-01-14 07:46 · Score: 1

First define a known force. Right now the unit of force is defined in terms of a kilogram.
That's easy! Gravity, of course!
Re:Gravity is not constant... by TomGreenhaw · 2014-01-14 07:50 · Score: 1

Not to be nit-picky, but force and gravity are the same thing (http://en.wikipedia.org/wiki/Equivalence_principle) When we're talking about variations on the scale of a few atoms, everything matters including some normally imperceptible forces due to the relative positions of everything and small electrostatic forces as well.

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Re:Gravity is not constant... by Baloroth · 2014-01-14 08:07 · Score: 4, Informative

That approach is in fact one of the proposals for a replacement to the kilogram. The problem is counting 10^23 atoms of a material (and getting pure material to work with).

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Re:Gravity is not constant... by Seraphim1982 · 2014-01-14 08:15 · Score: 1

The current (early 2011) uncertainty in Avogadro number is about 30 ppb. The current uncertainty in the hunk of metal is about 20 ppb. I don't think the International Committee for Weights and Measures would consider making a switch unless it is one that would reduce uncertainty.
Re:Gravity is not constant... by Minwee · 2014-01-14 08:31 · Score: 1

You're getting weight and mass mixed up. That's pretty common, especially if you are used to using the same unit for both.
Suppose that you have two scales, one of which measures weight (perhaps with a spring) and the other mass (the balance I mentioned earlier). If you place an object with a mass of one kilogram on each scale, in a gravitational field of exactly one g, then the first scale will measure 2.2046 pounds of weight and the second 1.000 kilograms of mass.
If you travelled to Mars where the gravity is 0.38 g, the first scale would only measure 0.836 pounds of weight but the second would still measure exactly one kilogram of mass. Weight, the force on an object due to gravity, will change in differing gravity but mass will not.
Re:Gravity is not constant... by mspohr · 2014-01-14 08:32 · Score: 1

It's turtles all the way down.

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Re:Gravity is not constant... by Existential+Wombat · 2014-01-14 08:34 · Score: 1

A duck.
Is that a European or African duck?
Oops, wrong sketch...
Re:Gravity is not constant... by Electricity+Likes+Me · 2014-01-14 09:10 · Score: 1

There's also the problem of making the standard practical, and distributable. A perfect standard that you can't use to create secondary standards is useless. A perfect standard that can't be replicated reasonably widely is also useless.
Re:Gravity is not constant... by sjames · 2014-01-14 09:33 · Score: 1

And therein lies the problem.
Re:Gravity is not constant... by maxwell+demon · 2014-01-14 09:55 · Score: 1

Placing two masses on a balance is the usual method
Yes, and the process of placing two masses on a balance is known as weighting.

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Re:Gravity is not constant... by maxwell+demon · 2014-01-14 10:02 · Score: 1

Comparing it to another mass using a balance makes any variation in the force of gravity irrelevant.
No. The two masses are not at the same spot, and therefore if the force differs between the left and the right side of the scale, this affects your measurement. (As an extreme case, imagine a microscopic black hole located under one of the two sides.)
Of course you can check this by just exchanging the two masses to be compared and then repeating the measurement. If the scale again is in balance, the masses are equal. Otherwise, the forces on both sides are different, and so are the masses.

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Re:Gravity is not constant... by lgw · 2014-01-14 10:47 · Score: 1

Good plan. Now if only we had a reference force ...

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Re:Gravity is not constant... by dwywit · 2014-01-14 11:29 · Score: 1

Sounds like the two-watch problem from 17th century naval navigation - if you have two watches, which one shows the correct time? So you use three or more watches to reduce inaccuracy.
How about a three or four-way balance? Instead of a simple two-sided balance beam, set up a triangular or square arrangement. If the reference kilograms are identical to the master kilogram, the balance will be level. If the balance is down in one corner, you've immediately spotted the item/s that aren't quite right. Of course, if you're using four items in a square configuration, and an entire side (two items) dips downwards, you're back to the original problem.
On second thoughts, this isn't a very good solution at all. Carry on.

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Re:Gravity is not constant... by cfulton · 2014-01-14 11:44 · Score: 1

Yes but to flog the dead horse just a little more...IT DOESN'T MAKE A DIFFERENCE. If you are using a balance to compare the mass of two objects and the objects have the same mass, they will balance on the moon or in the upper atmosphere or on a neutron star. But, the question of the amount of mass still hasn't been solved without a reference mass and that (the one outside of Paris) keeps changing a little bit all the time.

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Re:Gravity is not constant... by LordLimecat · 2014-01-14 12:51 · Score: 1

IIRC, they already had multiple reference objects.
Re:Gravity is not constant... by ckblackm · 2014-01-14 13:24 · Score: 1

Aflac!
Re:Gravity is not constant... by Rich0 · 2014-01-14 15:18 · Score: 1

The whole problem with these approaches is that for all its flaws that hunk of metal works remarkably well. There have been many attempts to replace it for all the obvious reasons.
I think silicon is one of the big contenders for the atom to count because the electronics industry has gotten so good and preparing samples of it at incredibly high purity. However, creating a sample of known density and volume at a scale large enough to measure its mass is very difficult. It isn't like you can just grab NA C-12 atoms with tweezers and stick them in a pile. It would be a chore keeping out all the non-Carbon atoms, let alone the isotopes of carbon. And of course if you get any C14 in there then there will be non-Carbon atoms in due time.
Re:Gravity is not constant... by Minwee · 2014-01-14 15:32 · Score: 1

Scales calculate mass by measuring the force exerted by gravity.
Not this kind. By comparing the torque exerted on both sides of the balance, you can directly find the relation between the mass on the pan and the masses of the sliders. Since the sliders are of known mass, this method can determine the mass of an object without being affected by small changes in gravity.

Also, pounds are now defined in kilograms, so pounds are now indirectly a unit of mass.
There are pounds for mass and pounds for force. In standard Earth gravity their values are interchangeable, but they are still two different units measuring two very different things. This is one of many reasons why it is preferable to use SI units like Newtons and kilograms where there is any chance for confusing the two.
Re:Gravity is not constant... by Electricity+Likes+Me · 2014-01-14 18:47 · Score: 1

All proposed gravitation based standards are less accurate then then current kilogram standard (gravity is too weak to be meaningfully measured accurately in the lab - after all, it takes a whole planet to supply 1kg of force on the current standard!).
Re:Gravity is not constant... by Hognoxious · 2014-01-14 20:25 · Score: 1

No it isn't. http://en.wikipedia.org/wiki/Weighting

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Re:Gravity is not constant... by IDtheTarget · 2014-01-15 02:05 · Score: 1

No shit. And measuring the mass of the slug in question involves weighing it. Or do you have another method involved for determining the mass of an object used as the constant for measuring mass?
Wow. Just....wow. So *this* is what modern education has come to?
Seriously, weight is an accelerational effect upon the mass by a force, in this case, gravity. Einstein taught us that any acceleration, outside of a frame of reference, would be identical. So, providing an acceleration by means of some other force while in microgravity would accomplish the same thing.
I suggest that you do a quick Google search on the subject. In about 5 seconds I found articles on using springs on the ISS, and a patent application for using a centrifuge to accomplish the same thing.
Re:Gravity is not constant... by Minwee · 2014-01-15 03:41 · Score: 1

Thank you for restating my original point.
Re:Gravity is not constant... by DMUTPeregrine · 2014-01-17 21:02 · Score: 1

The slug is the English system unit of mass. It made much more sense to use the pound for weight and the slug for mass, but doing things in the sensible manner has never been the English system's strong suit.

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Re:yeah because imperial by Chris+Mattern · 2014-01-14 06:07 · Score: 3, Funny

I prefer rebel units. If you can't depend on Luke Skywalker for your calibrations, who can you trust?

Bah, I say by dmatos · 2014-01-14 06:07 · Score: 3, Interesting

The Ampere was only chosen as an SI fundamental unit because it was easier to measure than a Coulomb. To me, an Ampere will always be 1 Coulomb per second.

And since the electric charge is 1.602E-19 Coulombs, we can just invert that number to find the number of electric charges (ie, electrons) in a Coulomb.

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Re:Bah, I say by inode_buddha · 2014-01-14 06:14 · Score: 2

Here's what I don't understand, whats so wrong about defining the Ampere in terms of coulombs per second? Or in terms of anything else for that matter? I guess I fail to see whats so bad about having the Ampere as a derived unit.

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Re:Bah, I say by Chris+Mattern · 2014-01-14 06:24 · Score: 3, Informative

And since the electric charge is 1.602E-19 Coulombs, we can just invert that number to find the number of electric charges (ie, electrons) in a Coulomb.
Well, yes. But the point here isn't shuffling around the units. The point here is to increase the accuracy at which the elementary charge is known, which would be necessary whether you're defining the Ampere in terms of the charge or the Coulomb in terms in the charge. Currently, we know the elementary charge to ten decimal places. That's not good enough, so that's what this is about--finding out that figure to greater accuracy so it can be used as a universal measurement standard. For comparison, the definition of the second is accurate to 15 decimal places.
Re:Bah, I say by gstoddart · 2014-01-14 06:44 · Score: 1

Here's what I don't understand, whats so wrong about defining the Ampere in terms of coulombs per second?
Really? Because this sounds like it's a pretty darned hand-waving definition to me.

At present, an ampere is defined as the amount of charge flowing per second through two infinitely long wires one meter apart, such that the wires attract each other with a force of 2x10^-7 newtons per meter of length. That definition, adopted in 1948 and based on a thought experiment that can at best be approximated in the laboratory, is clumsy
Where, for instance, are you going to get two infinitely long wires? How are you going to guarantee they're precisely 1m apart? How do you precisely measure 2x10^-7 newtons per meter of length?
If your measure can "at best be approximated in a laboratory", you don't have an objective measure, you have a vague description of what you mean.

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Re:Bah, I say by inode_buddha · 2014-01-14 07:12 · Score: 1

That was what I meant. Where are you going to get 2 infinitely long wires?
You won't.
And that is why you should have a derived definition for the Ampere. Such as coulombs per second, or volt per ohm.

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C|N>K
Re:Bah, I say by gstoddart · 2014-01-14 07:16 · Score: 1

And that is why you should have a derived definition for the Ampere. Such as coulombs per second
Except, as has been pointed out elsewhere here, the Coulomb is defined in terms of Amps.
So, if you defined the Amp in terms of the Coulomb, and the Coulomb is defined in terms of Amps ... you end up with a circular definition.
I don't get the impression you *can* define a Coulomb independent of the Amp.
I think what they're trying to find is a precise way to define the foundation of both of these.

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Re:Bah, I say by UnknownSoldier · 2014-01-14 07:37 · Score: 1

> I guess I fail to see whats so bad about having the Ampere as a derived unit.
The point of Physics is to simply everything down into fundamental units. Adding a derived unit just "clutters" that goal.
Re:Bah, I say by Seraphim1982 · 2014-01-14 08:48 · Score: 1

Just say the Coulomb is 6.24150965e×10^18 * (the charge on an electron), and the amp is 1 C/s. The resulting 25ppb uncertainty in the definition of the Coulomb is probably better then anything you'll get out of trying to realize the current standard.
Re:Bah, I say by tibit · 2014-01-14 08:55 · Score: 1

You're making up problems. The way it would be done in practice is:
1. Set up a current-measuring system that internally counts the elementary charges. This is sufficient to measure real-life amps in terms of real-life e.
2. Tweak the value of e in Coulombs to make things work out :)

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Re:Bah, I say by sjames · 2014-01-14 09:58 · Score: 1

Because even with a really good magnifying glass and an a CPA turned into Super Accountant with a gamma ray treatment, it's hard to count all those electrons whizzing by fast enough.
Re:Bah, I say by maxwell+demon · 2014-01-14 10:47 · Score: 1

Which you can only do if you can count electrons. Since at the time the Ampere was defined, there was no hope to do that even approximately, it would have been a much worse definition than the one that was chosen.
Indeed, this very article is about now being able to do exactly this: Count electrons which pass a chip.

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The Tao of math: The numbers you can count are not the real numbers.
Re:Bah, I say by maxwell+demon · 2014-01-14 10:50 · Score: 1

Since at the same time the Coulomb would be removed as a derived unit (by promoting it to a fundamental unit), this would not be an argument.

--
The Tao of math: The numbers you can count are not the real numbers.
Re:Bah, I say by Electricity+Likes+Me · 2014-01-14 19:05 · Score: 1

Derived units are all over the place - science is positivist, you use whatever model makes it easiest to work with your data. The problem with the amp was that the definition of the standard was not realizable precisely - you can't have infinite wires, so you two wires of some length and hope you avoid end effects messing it up too much. Which means everyone trying to realize a standard amp gets it a little different as a result of the definition itself.
Then there's the problems of just making the wires longer (they get heavier, they sag, you have to worry about more space). The benefit of the new system is you could fit it on a benchtop, and it's exact - you count exactly that number of electrons and that gives you an amp definition, which anyone can recreate and which doesn't have a built-in uncertainty to its realization.

How an Ampere is defined will NOT change! by bobbied · 2014-01-14 06:13 · Score: 3, Insightful

The fine article is incorrect. How an Ampere is defined does not change.

What may change is how you can measure current in the lab using other known standards because it's really hard to count electrons. Or perhaps the way a Coulomb is defined may change but the Ampere will not change.

One Ampere will remain defined as One Coulomb per second.

--
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101

Re:How an Ampere is defined will NOT change! by barlevg · 2014-01-14 06:26 · Score: 4, Informative

Technically no. As noted above, the Ampere, not the Coulomb, is the fundamental unit. A Coulomb is an Ampere-second.
Re:How an Ampere is defined will NOT change! by cdrnet · 2014-01-14 06:35 · Score: 4, Informative

This is not entirely correct. Ampere is an SI base unit while Coulomb is a SI derived unit (defined as 1 C = 1 A s) - not the other way round.
Re:How an Ampere is defined will NOT change! by the+eric+conspiracy · 2014-01-14 07:21 · Score: 1

Oh SNAP. I always thought it should be defined as Avogadro's number of electrons per second.
Change it to that, please.
Then it would have made the calculations I have to do as an electrochemist much simpler.
Re:How an Ampere is defined will NOT change! by UnknownSoldier · 2014-01-14 07:41 · Score: 1

Ampere pretends to be an SI base unit even though it is derived from kg
FTFY.
My emphasis added:

Nevertheless, because of the way they are deïned, three other base units of the SI call upon the deïnition of the kilogram, namely the ampere, the mole and the candela. Thus, any uncertainty inherent in the definition of the kilogram propagates also into these units.

* http://www.acs.org/content/dam/acsorg/about/governance/committees/nomenclature/meetings/2007-fall-attachment-01a.pdf
Re:How an Ampere is defined will NOT change! by maxwell+demon · 2014-01-14 10:59 · Score: 1

Actually the meter started its life as 1/10,000,000 of the length of meridian going through Paris, from the pole to the equator (You thought it was an accident that the circumference of the earth is extremely close to 40,000 km?) Of course that wasn't exactly a practical thing to measure (although it was measured once exactly for that reason), therefore they used that bar for the length.
Also the kilogram started out as the mass of one liter of water.

--
The Tao of math: The numbers you can count are not the real numbers.
Re:How an Ampere is defined will NOT change! by maxwell+demon · 2014-01-14 11:00 · Score: 1

Just define your own electrochemical system of units. ;-)

--
The Tao of math: The numbers you can count are not the real numbers.

As long as they dont change it by viperidaenz · 2014-01-14 06:18 · Score: 1

And ohms law still works out. ... hang on, that's already a nice easy calculation to define and Ampre. I = E/R

Re:As long as they dont change it by barlevg · 2014-01-14 06:27 · Score: 1

The Ohm is a derived unit (depends on the Volt and the Ampere). So no, sorry.
Re:As long as they dont change it by viperidaenz · 2014-01-14 07:25 · Score: 1

It still better stay pretty much the same, or we'll have two definitions of the ohm.
Re:As long as they dont change it by barlevg · 2014-01-14 07:40 · Score: 1

My point was that you can't define the Amp in terms of Ohms, because then you end up with 1 Ohm = 1 Ohm. Very useful definition indeed.
Re:As long as they dont change it by mevets · 2014-01-14 09:41 · Score: 1

Would it be shocking if electric unit definitions themselves formed a circuit?
Thank you very much, Iâ(TM)ll be here all week.

Re:yeah because imperial by martinux · 2014-01-14 06:19 · Score: 4, Funny

Force was redefined in the prequels as midichlorians multiplied by anger. Conveniently it's kept the same equation:

f = ma

Re:actually it's not, by barlevg · 2014-01-14 06:19 · Score: 1

Actually, the Imperial Pound is legally defined as exactly 0.45359237 kilograms. It is (but possibly has not always been?) a unit of mass. Citation.

Re:Are we even sure all electrons are the same? by barlevg · 2014-01-14 06:24 · Score: 2

Charge is quantized. This has been known since Millikan. You can't ever arrive at an electron-and-a-half of charge (though you can, in theory, get a third or two thirds, but not naturally in nature).

Re:Are we even sure all electrons are the same? by barlevg · 2014-01-14 06:25 · Score: 1

Crap. I did just type "naturally in nature."

Re:yeah because imperial by mmell · 2014-01-14 06:28 · Score: 2, Insightful

Well, Imperial units are binary (1/2", 1/4", 1/8" tools, for example). Twelve inches in a foot divides evenly by two, three, four, six. Thirty-six inches in a yard has a lot of factors too. 5,280 feet in a mile seems arbitrary until you start counting the factors. Three hundred sixty degrees in a circle can evenly be divided by 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18... - tried that with radians lately? One hundred eighty degrees separate water freezing from water boiling - 180, another composite number with lots of factors. If you're an engineer, there's a lot to be said for Imperial or SAE units - they sure make a lot of the math easier.

On the other hand, Metric is decimal. Last time I checked, everyone had ten fingers. We count base ten. Computers may be great at binary, but most of us do arithmetic for our daily tasks at base ten.

Binary (Imperial) has its place. Decimal (Metric) has its place. And never the two shall meet . . .

A modest editorial proposal by TheloniousToady · 2014-01-14 06:31 · Score: 4, Funny

How about we change "At present, an ampere is defined as" to "Currently, an ampere is defined as"?

Re:A modest editorial proposal by TheloniousToady · 2014-01-14 07:02 · Score: 1

I guess whoever marked the parent as "Flamebait" didn't get the "Currently" joke. The use of "a modest [editorial] proposal" in the title was a hint, but I guess that wasn't enough. :-)
Re:A modest editorial proposal by EmagGeek · 2014-01-14 07:03 · Score: 2

What idiot moderated this as "Flamebait" when it is clearly "Funny?"
Who the hell is in charge of this place?
Re:A modest editorial proposal by gstoddart · 2014-01-14 07:13 · Score: 1

Who the hell is in charge of this place?
Nobody is in charge.
Dice owns it. The 'editors' are barely literate, can't spot dupes, and are in charge of periodically adding stories. There's a team of incompetent coders furiously working on the beta site they occasionally force me to see.
Once you hit the moderation system ... it's monkeys flinging poo. ;-)

--
Lost at C:>. Found at C.
Re:A modest editorial proposal by TheloniousToady · 2014-01-14 07:14 · Score: 1

Glad you got it, thanks for your support. I'll keep trying, though clearly some part of the population here suffers from HDD, Humor Deficit Disorder, so I guess we gotta live with that.
Re:A modest editorial proposal by EmagGeek · 2014-01-14 08:47 · Score: 1

I'll ask it again.
Who is in.... *charge* ... of this place?
Get it? "Charge?"
Ugh...
Re:A modest editorial proposal by maxwell+demon · 2014-01-14 11:07 · Score: 2

Well, some people just don't have the capacity to get the jokes.

--
The Tao of math: The numbers you can count are not the real numbers.

Re:what? by skids · 2014-01-14 06:33 · Score: 1

My car does zero to 3.3 european swallow airspeed velococities (unladen) in 9.7 seconds. What does yours do?

--
Someone had to do it.

Re:Are we even sure all electrons are the same? by jeffb+(2.718) · 2014-01-14 06:37 · Score: 1

If not all electrons have the same charge, we have much bigger problems than our standard for measuring current.

As fundamental assumptions in physics go, you can't get much more fundamental than that.

Re:Are we even sure all electrons are the same? by oracleofbargth · 2014-01-14 06:44 · Score: 1

Erk...

Couldn't decide whether to be pedantic about partial charges, or abuse of the English language...

Congratulations, you have broken my pedantry filter.

Re:Are we even sure all electrons are the same? by barlevg · 2014-01-14 06:53 · Score: 1

Interesting. I actually wasn't aware of the concept of partial charges before today (I guess they don't teach this kind of stuff to physicists). But, as I read it, this is some sort of shielding effect, and the integer number of charges is still present in the molecule.

Charge of an electron? by tomhath · 2014-01-14 06:59 · Score: 1

redefine the amp on the basis of e, a physical constant representing the charge of an electron.

Until some smarty pants physicist comes along and determines that e or the charge of an electron changes depending on [pick something, this is physics after all]

Re:Charge of an electron? by maxwell+demon · 2014-01-14 11:13 · Score: 1

The energy scale you are scattering at?
See also: running coupling constant

--
The Tao of math: The numbers you can count are not the real numbers.

Re:actually it's not, by mythosaz · 2014-01-14 07:00 · Score: 1

Pretty sure a Pound is worth about $1.64.

*shrug*

Re:what? by leonardluen · 2014-01-14 07:06 · Score: 1

you have nothing to worry about they aren't changing the value that an amp is on your multimeter.

what is happening is that now in extremely high precision experiments they can now measure an Amp down to say 15+ decimal places using the new definition. previously they had no way to calibrate their equipment to that degree of accuracy.

Re:Are we even sure all electrons are the same? by msauve · 2014-01-14 07:07 · Score: 1

Most physicist don't believe electrons have the same charge. Separate but equal, yes. Same, no. But there is a one electron theory, where all electrons would have the same charge.

--
"National Security is the chief cause of national insecurity." - Celine's First Law

can at best be approximated by Arancaytar · 2014-01-14 07:13 · Score: 1

Huh? You don't have two infinite lengths of wire lying around? They're fairly easy to get; you just take one infinitely long wire and cut it in half.

More seriously though, what's wrong with just reversing the definition (1 A := 1C/s rather than 1C := 1As), and then redefining 1 Coulomb as a precise number of electrons?

Re:can at best be approximated by Arancaytar · 2014-01-14 07:17 · Score: 1

(Addendum: wait, never mind, that's basically their proposal with an additional step via Coulomb.)
Re:can at best be approximated by Krishnoid · 2014-01-14 11:47 · Score: 1

Huh? You don't have two infinite lengths of wire lying around? They're fairly easy to get; you just take one infinitely long wire and cut it in half.
No, then you'd have two semi-infinite lengths of wire.
Oh wait, you meant lengthwise. Got it.
Re:can at best be approximated by DMUTPeregrine · 2014-01-18 02:15 · Score: 1

Nope, either way works. That's the fun thing about infinite lengths.

--
Not a sentence!

Re:yeah because imperial by operagost · 2014-01-14 07:15 · Score: 1

The formula describing my response to the introduction of the midichlorians in Episode 1 is as follows:

FinA!

--

Gamingmuseum.com: Give your 3D accelerator a rest.

Re:what? by operagost · 2014-01-14 07:18 · Score: 1

40 rods to the hogshead... and that's the ways I likes it!

--

Gamingmuseum.com: Give your 3D accelerator a rest.

Zap by wbr1 · 2014-01-14 07:23 · Score: 1

I am shocked.
My puny brain doesn't have the power to Coulomb through this information.
However, I am sure my fellow slashdotters can tell me Watt is going on.
Maybe a car analogy using the Chevrolet Volt?
If Joule help me, I can make it worth your while.

--
Silence is a state of mime.

Re:yeah because imperial by UnknownSoldier · 2014-01-14 07:35 · Score: 1

Great example! Hope you get modded up for being able to see the strengths and weakness of both systems and knowing when to use one or the other!!

Organic System - ad hoc but makes certain calculations easy, conversions difficult.
Scientific System - systemic and mathematically "clean" but simplifies conversions.

There is a reason we use base 60 for time. I don't see too many people wanting to switch our clocks over to base 10.

Operation Neptune Spear by tepples · 2014-01-14 08:01 · Score: 1

My country's Black Hawk helicopter does one to zero terrorists (binladen) in roughly 9 years and 8 months.

Interesting YouTube video regarding the Kilogram by Ngarrang · 2014-01-14 08:02 · Score: 2

http://www.youtube.com/watch?v=ZMByI4s-D-Y

This youtube video answered most of my questions about the kilogram.

--
Bearded Dragon

Re:Are we even sure all electrons are the same? by Tough+Love · 2014-01-14 08:07 · Score: 1

You can't ever arrive at an electron-and-a-half of charge (though you can, in theory, get a third or two thirds, but not naturally in nature).

And not artificially either, by any accepted theory and in spite of many experimental attempts.

--
When all you have is a hammer, every problem starts to look like a thumb.

Re:Are we even sure all electrons are the same? by barlevg · 2014-01-14 08:19 · Score: 1

Right. Because the energy required to separate two quarks is so great it ends up creating a quark and an anti-quark, which just fuse with your separated quarks to form two new hadrons.

Ah Physics! by oscrivellodds · 2014-01-14 08:50 · Score: 1

What I'd like to know is why are units named after people? It is just crazy. If you want to honor a physicist, erect a statue to him/her. Why name a unit after them and obfuscate the meaning of the unit? What is a Newton? What is an Ampere? What is a Volt? How can you use such a unit in dimensional analysis? Naming a unit after someone guarantees extra effort and adds a layer of obstruction for anyone to learn and understand more physics. It hides the physical meaning of the process/properties that underlie the unit. If I were a physicist and they asked me if I wanted some constant/complex unit named after me, I'd say hell no. Physics is tough enough without pointlessly naming units after people.

And what is up with the Ohm and the Siemen? One of those guys got a free pass...

Re:Ah Physics! by wonkey_monkey · 2014-01-14 09:02 · Score: 2

Why name a unit after them and obfuscate the meaning of the unit?
Why is a second called a second? Why is a (kilo)gram called a (kilo)gram? Why is a mole called a mole?
I have no idea about any of those, but I don't have any trouble remembering what they are the units of.
What's so confusing about re-using a scientist's name? Would you prefer "time unit" or "mass unit"?

--
systemd is Roko's Basilisk.
Re:Ah Physics! by TeknoHog · 2014-01-14 09:55 · Score: 1

Why is a second called a second? Why is a (kilo)gram called a (kilo)gram? Why is a mole called a mole?
I have no idea about any of those, but I don't have any trouble remembering what they are the units of.
What's so confusing about re-using a scientist's name? Would you prefer "time unit" or "mass unit"?
In other words, it's good to have different words for different things. If you need to make up a new word, then might as well base it on a person's name, instead of making it completely random or making awkward combinations of old words.
The only slight problem, IMHO, with person-based words is that they can't really be translated, and you may need to do some arbitrary transliteration in other languages. Then again, I think it's better for science to use the same words in all languages. For example "energy" is basically the same in many different languages.

--
Escher was the first MC and Giger invented the HR department.
Re:Ah Physics! by maxwell+demon · 2014-01-14 11:19 · Score: 1

Why is a second called a second?
Because it is the second subdivision of the hour into 60 parts (the first one being the minute).
Note that the same terms are also used with angles (arc minutes/arc seconds), except that here it is the degree which is divided.

--
The Tao of math: The numbers you can count are not the real numbers.
Re:Ah Physics! by oscrivellodds · 2014-01-20 04:57 · Score: 1

A gram, second, and mole are fundamental units. They can be used in dimensional analysis. A Newton is a kg-m/s^2. I don't know what a Newton is, but I have experience with kg, meters, and seconds. I can use kg-m/s^2 in dimensional analysis to gain some insight about a calculation. A Newton? Not so much. You have to constantly translate named units into fundamental units to make sense of them.
Why stop with the current crop of units named after people? A m/s^2 describes acceleration. Why don't we just call it a Smith (or whoever). Then a Newton will become a kg-Smith. Nothing wrong with that... And what about 1/sec? Let's call that a George. Now a speed can be expressed as a m-George! A Newton can be converted to a kg-m-George^2. 1 Smith = 1 m-George^2. Great! That will help people understand physics!

Re:yeah because imperial by tibit · 2014-01-14 08:51 · Score: 1

It all only makes a difference if you do things by hand. When you do engineering drawings, the CAD system handles all that for you and it doesn't matter how evenly things divide out. When it's made in quantity, it's machined using various CNC systems, and those don't care about it either. Maybe a machinist would, if they use the old way of doing things and don't have numerical readouts.

--
A successful API design takes a mixture of software design and pedagogy.

Re:yeah because imperial by H0p313ss · 2014-01-14 10:17 · Score: 2

And never the two shall meet . . .

Except over Mars.

... fleetingly...

--
XML is a known as a key material required to create SMD: Software of Mass Destruction

Newton's Second Law by Repentinus · 2014-01-14 10:21 · Score: 1

How was the general form of Newton's 2nd Law defined in the prequels?

Re:yeah because imperial by isama · 2014-01-14 10:31 · Score: 1

I'd want to. also we should remove timezones from this world.

Re:yeah because imperial by maxwell+demon · 2014-01-14 10:37 · Score: 1

Well, Imperial units are binary (1/2", 1/4", 1/8" tools, for example).

Those all use the very same unit, the inch. The fact that you like to use binary fractions as number before that is completely unrelated to the unit as such. You could as well use 1/2 m, 1/4m, 1/8 m in the metric system (note that for the liter, those are indeed quote common).

Three hundred sixty degrees in a circle can evenly be divided by 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18... - tried that with radians lately?

Now this is completely unrelated to metric vs. imperial units.

--
The Tao of math: The numbers you can count are not the real numbers.

Re:This is why I laugh.... by cfulton · 2014-01-14 12:02 · Score: 1

The English system of measurements has the exact same problem with the pound because...Here it comes a pound is defined as 0.45359237 kg. And we are back to the bar sitting just outside of Paris.

--
No sigs in BETA. Beta SUCKS.

Re:yeah because imperial by geekoid · 2014-01-14 12:48 · Score: 1

If you can't do the calculation, you don't understand the calculations.

--
The Kruger Dunning explains most post on /. http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

Comment removed by account_deleted · 2014-01-15 05:48 · Score: 1

Comment removed based on user account deletion

Re:yeah because imperial by TangoMargarine · 2014-01-15 06:22 · Score: 1

http://en.wikipedia.org/wiki/Metric_calendar

--
Unity? Screw that: XFCE. Slashdot Beta? Screw that: SoylentNews. Australis? Screw that: Pale Moon. UX developers DIAF

Re:Are we even sure all electrons are the same? by TangoMargarine · 2014-01-15 06:24 · Score: 1

Does having the same charge ensure they have the same "weight"?

--
Unity? Screw that: XFCE. Slashdot Beta? Screw that: SoylentNews. Australis? Screw that: Pale Moon. UX developers DIAF

Now the new polarity by slimepit · 2014-01-15 15:15 · Score: 1

Now we need differentiate the right or left rotation of electrons in the valance ring. Then determine which rotation of electron to allow to pass, jump to a higher energy level or freeze both rotations from passing. Just a thought...................

Re:yeah because imperial by tibit · 2014-01-17 04:24 · Score: 1

Doing things the old way without the readouts was co-adapted to how the machines were designed. You have a divider, it offers a fixed set of angles, and the designs are made to be machined with those dividers in mind. The axis cranks on the mills/lathes were labeled in a certain way, say with binary imperial fractions, and the designs were made to utilize that. And so on. Yes, I'm talking about quite old-style machines, probably last made half a century ago, but still. A modern CAD drawing would make a 1950's machinist go nuts with excitement: just look at how many extra hours I can bill for that!

--
A successful API design takes a mixture of software design and pedagogy.

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Ampere Could Be Redefined After Experiments Track Single Electrons Crossing Chip

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