Standard Kilogram Gains Weight 177
mrbluze writes "The standard kilogram weights used by countries around the world for calibration have variably increased in mass by tens of micrograms. This poses a threat to the precision and comparability of measurements in science, engineering and trade. The problem is due to surface contamination, but a safe method of cleaning the weights has only recently been devised by the use of ozone and ultraviolet light (abstract). 'The ultraviolet light-ozone treatment removes hydrocarbon contamination that has built up on the metal surface, gunk that comes from the emissions of an industrial society. Cumpson suspects that because the kilos living in national labs have been retrieved and handled more frequently than the international kilo, more carbon-containing contaminants have built up on them over time. Incubating the kilograms with a set amount of ozone and ultraviolet light "gently breaks up the carbonaceous contamination at the surface."'"
Excellent (Score:5, Funny)
I think the kilogram should be adjusted upwards every holiday season ...
Nothing like a bit of seasonal normalisation on the scales to justify festive binges.
Re:Excellent (Score:5, Funny)
I came here to ask precisely this.
So I've actually lost weight? Woohoo! go science!
Mititant metric user (Score:2)
BTW: we've spoken with the frenchies, they'll stop feeding the standard KG more than one bacon and cheese croissant per day.
Re:Mititant metric user (Score:5, Informative)
French do not eat bacon and cheese croissant...
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Maybe not, but their standard weights do. Darn things just can't get enough bacon and cheese.
Re:Mititant metric user (Score:5, Funny)
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And BTW, ham, cheese and "bechamel" croissant is really tasty [ceinfo.fr]. One could easily replace the ham with crispy bacon.
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I had no idea they added bechamel as well. It's amazing you guys can even walk.
Must be all the red wine... or the sex...
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French do not eat bacon and cheese croissant...
Only fries and toast, right?
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Sorry, there's no such thing as a "standard ounce". The legacy units are defined terms of SI units.
So there is a standard ounce.
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I think there's at least two standard ounces: the Troy ounce (used for gold and other precious metals, = 31.1034768 g) and the Avoirdupois ounce (the 'common' ounce, = 28.349523125 g). Also there is a liquid measure, the fluid ounce, but that's another topic. And TIL that avoirupois is from Old French, meaning "goods of weight".
There are also less-used ounces, including the Apothecaries' ounce, the Maria Theresa ounce, the Spanish ounce, and a couple of different metric ounces. And the ounce-force, and
begs the question... (Score:2)
Use the method they used to determine this to define 1KG
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how do they know this reliably?
Use the method they used to determine this to define 1KG
Yep.
The summary itself says "...the kilos living in national labs have been retrieved and handled more frequently than the international kilo".
ie. Some of them are stored more carefully than others and aren't gaining as fast.
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four US "standard kilos" compared 24 years ago (Score:2)
Re:begs the question... (Score:5, Informative)
Isn't the definition of a gram the mass of 1 cm3 of water?
No, that was how it was initially defined but in 1799 they moved to using metal prototypes.
Would this not be a standard you could employ in any lab without the need for the international 1Kg prototypes?
It's trickier than it sounds. Between the difficulty of accurately measuring out the liquid, the fact that density changes with temperature and pressure, the fact that isotopic mixes can vary and the fact that our units of pressure are in themselves based on the kilogram making the definition recursive this becomes a difficult definition to apply accurately.
There is talk of moving to a definition based on fundamental physical units but it's difficult to get the experimental results consistent and stable enough (IIRC two different methods for determining avagadros number were giving slighly different results).
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(IIRC two different methods for determining avagadros number were giving slighly different results).
I wonder if it may be easier to define Avogadro's number as a given constant and derive the kilogram as a fraction of a mole of a known isotope, like 1/12 of a kmole of C-12 (or maybe 1/4 of a kmole of He-4, to reduce the loss of energy in chemical bonds). Of course, this moves the difficulty to counting an exact number of similar atoms and measuring their mass precisely but at least it ties the kg to a physical value instead on an arbitrary metal lump.
Re:begs the question... (Score:5, Informative)
That was the original definition, but it's not precise enough. It's extremely difficult to get water with an exact isotopic composition. VSMOW is used, but even that is not reliably reproducible to the necessary level of precision.
http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water [wikipedia.org]
Also, the density of water is very much related to the temperature and air pressure. Pressure is measured as a unit of force per unit area. Typically, Newtons per squre metre (the Pascal unit). Force, is then in turn defined as a unit of mass times acceleration, with the Newton being 1 kg * 1 ms-2, which obviously results in a cyclically dependent definition, because it would be defined as 1 kg of pure water at a specific temperature and pressure measured in:
Pa = N/m^2 = kg/m*s^2
To get around this problem, you would need to define the Newton in terms of its relationship to other units, ultimately ending up linked to a fundamental constant of nature. The Watt balance approach is trying to do this, by linking the definition with the Ampere. That would reverse the relationship of the Ampere, which is currently defined in relation to the kilogram.
That would then gives a direct way to link those units with the kilogram, and there is no need to precisely measure 1 cubic decimetre of water. You just develop an extremely precise scale that can measure any test mass very precisely and accurately based on the new definition. The difficulty is actually putting that into practice and eliminating as much measurement error as possible. NIST and other laboratories around the world are trying. The problem is, the margin of error in the measurements are still higher than desired.
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Because the definition of a unit has to be implementable as a measurement, so that it can be used to calibrate scales. A purely theoretical definition may be exact, but it is also completely useless if you can't actually build a scale.
And as we can't count hydrogen atoms, this one doesn't work.
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They are much, much easier.
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Sadly, no. The definition of the kilogram is garbage due to it _imprecision_.
"It is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Four of the seven base units in the SI system are defined relative to the kilogram so its stability is important."
http://en.wikipedia.org/wiki/Kilogram [wikipedia.org]
"In a note to the CIPM in October 2009, Ian Mills, the President of the CIPM Consultative Committee - Units (CCU)
Ha! (Score:5, Funny)
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i love how people bring that up even though it was never the definition of the unit.
Re:Ha! (Score:4, Interesting)
How does a geek lose weight? (Score:5, Funny)
He (or she) redefines the standard.
Now all we need are electronic scales that can receive updated firmware via the internet.
Glad to be an American. (Score:5, Funny)
Re:Glad to be an American. (Score:5, Funny)
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The "Pound" is used to weight American Beef, the "Kilogram" is used to measure things like Uranium. Surely you can join the dots from there...
two things... (Score:5, Informative)
Although I'm sure you're kidding, it's probably worth bringing up the following 2 bits of trivia
1. Sadly, the American "pound-weight" has mostly been defined in terms of the kilogram and has its most recent official relationship updated in 1959 (now exactly 0.45359237 kg, down from 0.4535924277 kg back 1901).
2. The kg artifact itself is soon to be rendered obsolete. In 2014, the kg is likely to be redefined in terms of the planck constant (well technically, planck constant will be fixed to a specific number and since it has the units kg*m^2/s, and the second and meter are defined in terms of oscilations of a Ce133 atom and the speed of light, these will now determine the kilogram).
That is until we discover a grand unifying theory where the Planck constant is not actually a constant. Then you can really see the world unravel...
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2. The kg artifact itself is soon to be rendered obsolete. In 2014, the kg is likely to be redefined in terms of the planck constant (well technically, planck constant will be fixed to a specific number and since it has the units kg*m^2/s, and the second and meter are defined in terms of oscilations of a Ce133 atom and the speed of light, these will now determine the kilogram).
I suspect that you are a little bit confused. "Planck constant" has no real meaning without agreeing on some units beforehand, and "some specific number" certainly doesnt convey the likely choice.
The Planck Units [wikipedia.org] are based off the 5 known fundamental physical constants of the universe, where each constant is given the non-arbitrary value of exactly 1.0.
you can read all about then new kg (Score:3)
You can read all about the new kg here [bipm.org]...
Re:You are worng -- no ! (Score:2)
It seem that the legal definition of pound is bound to the kilogram: http://en.wikipedia.org/wiki/Pound_(mass) [wikipedia.org]
"The pound or pound-mass (abbreviations: lb, lbm, lbm, [1]) is a unit of mass used in the imperial, United States customary and other systems of measurement. A number of different definitions have been used, the most common today being the international avoirdupois pound which is legally defined as exactly 0.45359237 kilograms."
This is not a surprise as the USA have, from the international point of
Re:You are wrong (Score:5, Informative)
Perhaps you should read this document [nist.gov] from NIST about the history of weights and measures in the US.
According to this document...
1827 a troy pound was obtained from London.
1828 a brass artifact (which was compared to this troy pound) declared standard for the US mint, not the avoirdupois pound
1866 the metric system was made lawful for commerce in the US. Legally defines avoirdupois pound as (1/2.2046) kg
1875 17 governments (incl the US) established the international bureau of weights and measures
1890 The US receives standard kilogram artifacts #4 and #20 for use as the national prototype
1894 The US tweaks the definition of the pound relative to this kilogram artifact to make it closer to the UK pound
The US makes various other tweaks over the years in the pound's definition relative to the standard kilogram artifact that the US government maintains.
The "troy" pound artifact is only used for Mint operation in the US and is not related to the avoirdupois pound used in commerce.
Also all NIST calibrations are done in metric units (as of 1959).
Re: You are worng [sic] (Score:2)
In other words, the imperial values are pegged to the metric definition. The conversion values are not for "acceptable use" - they are the very definition.
NIST is where one of the copies of the standard kilogram is kept. NIST prefers SI standards.
http://www.nist.gov/pml/wmd/metric/metric-program.cfm [nist.gov]
Office of Weights and Measures "ensures traceability of state we
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Wow, you fail. If the US had some miraculous metal that could maintain a very constant mass, with greater accuracy than the IPK, then such a thing could also be used for the kilogram. But you are wrong, and they don't. Any artifacts the US does use for mass calibration, which includes at least their official copy of the kilogram, are also subject to the same kind of fluctation in mass that the international prototype kilogram is for many of the same reasons, if not more because it's handled far more frequen
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Nope. Feet are continually being renewed as part of a natural process and hundreds of new measuring cups are made every day, they don't have time to accumulate any gunk.
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Vive les idiots!
It's happening *everywhere* (Score:5, Funny)
I guess obesity really *IS* an epidemic problem.
Hey.... somebody had to say it.
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I guess obesity really *IS* an epidemic problem.
Hey.... somebody had to say it.
The point is the weigh gain isn't just an American problem
This affects all measurement units (Score:3, Informative)
Just to preempt all comments about imperial or home-grown measurement systems: All measurement systems in the world are defined from the metric base units, which are in turn defined from a few physical constants and this kilogram prototype. When the kilogram prototype gains mass, this affects the kilogram, pound, liter and fluid ounce equally.
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Just to preempt all comments about imperial or home-grown measurement systems: All measurement systems in the world are defined from the metric base units, which are in turn defined from a few physical constants and this kilogram prototype. When the kilogram prototype gains mass, this affects the kilogram, pound, liter and fluid ounce equally.
Not for me, I still define the pound as 7000 grains of barley. Must more stable than some unreliable reference standard that let's a little hydrocarbon tarnish screw it up
Why isn't there a precise atomic standard? (Score:3, Insightful)
Like there is for the second [wikipedia.org]:
"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."
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There's supposed to be a redefined kilogram based on the Planck Constant, but that hasn't happened yet. Not until 2014 will they talk about it again. Then maybe they can solve that problem.
Re:Why isn't there a precise atomic standard? (Score:5, Informative)
The mass of X number of molecules of element Y = 1 gram.
Like there is for the second [wikipedia.org]:
"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."
Because we don't yet have an accurate-enough measure of the Avogadro or Planck constants.
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The mass of X number of molecules of element Y = 1 gram.
Like there is for the second [wikipedia.org]:
"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."
Because it is hard to make a standard like that. Counting individual atoms on such a large scale is very complicated.
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The mass of X number of molecules of element Y = 1 gram.
First off, it should be atoms not molecules... Secondly, the atomic masses aren't actually constant between atoms. Primarily due to isotopes, but additionally due to electrons (though very minimal they too have mass), so you should also state the charge at least. Ah, but now we know of sub-atomic particles, and may even have discovered and measured the field / particle responsible for mass itself, so we should instead describe mass in terms of interaction with the Higgs Field...
Ah, but all the quantum
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Well,there is one proposed.
This is the Avogadro Project, one of two candidates for a redefinition of the kg, the other
being the Watt balance.
You take a lump of isotopically pure crystalline Si (Si 28) and optically polish it to a 'perfect' sphere.
You then use very accurate laser interferometry to measure the volume of the sphere (and with a suitable set
of measurements and model you can correct for any residual non-sphericity)
You use X-ray diffraction to measure the lattice spacing. You can now calculate the
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Every SI measure will cascade down the 'second' definition:
- second define meter
- second & meter define kilogram
- second, meter & kilogram define Kelvin
- etc etc
So we are seriously screwed if we ever decide time is not constant (at least with reference to caesium-133 at rest and 0 K)
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If that were ever found to be the case, then we could just redefine the second to something that is even more accurate than its current definition to resolve the problem. The new definition would define a new value that is within an acceptably small margin of error (probably on the order of a few femtoseconds or less), such that the new definition doesn't significantly alter the definition of any other units linked with it, at least within any measurable precision.
Revised Standard (Score:5, Informative)
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It is being worked upon, to make the kilogram a sphere of a specified diameter of a pure element. The element chosen is silicon and as a mm is defined very well this will avoid all these problems as a new standard can be made and measured repeatably in every country. Did work in this field some years ago with contact with the people involved.
Why didn't they stick with the good old 1 dm^3 of water?
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By the way: water is a universal dissolver. It dissolves literally everything (albeit slowly). So what are you going to make the container out of? As soon as you put the water in there it'll start contaminating the water. Now your dm3 of water is a bit more dense.
1 dm3 of water is good enough for 99.99% of all cases (guess), but not fo
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line the container with a protective sheet of plastic....
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woooosh? :-)
then just make it Plastic all the way down [google.de]
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"Old" is right. This was the standard from 1791 to 1795. Even in the eighteenth century, people considered this so bad a definition it was only in use for four years.
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I commented about this elsewhere in the thread, but basically, the density of water is dependent on pressure and temprature. Pressure is dependent on force and area. Force is dependent on mass and acceleration, which creates a cycilical definition. Also, the level of precision and accuracy that water can be measured is not high enough.
It used to be losing mass (Score:2)
A few years ago, the kilogram reference standard was losing mass -- coincidentally, they said it had lost 50 g, the amount of mass it's now said to have gained. So it should be just right by now.
http://www.sciencedaily.com/releases/2007/09/070921110735.htm [sciencedaily.com]
Re:It used to be losing mass (Score:4, Informative)
50g! Forget Avogadro's constant and spheres of silicon, I could do better than that with a brick and a shoebox.
Oh sorry, I typed "50 ug", but I used an ASCII "mu" but it seems to have been eaten by Slashdot and I didn't notice it in the preview. For the record, Slashdot doesn't accept the µ HTML entity either)
Re:It used to be losing mass (Score:5, Informative)
There is no ASCII mu. ASCII is a seven-bit encoding which only covers unadorned latin alphabetic characters, arabic digits, and some random punctuation. Even latin1 (aka ISO8859-1) lacks a mu character. I'm not sure what you think you typed, but it definitely wasn't ASCII.
There's also the problem of potential confusion between U+00B5 MICRO SIGN and U+03BC GREEK SMALL LETTER MU (among others), but neither of those is remotely ASCII.
Anyway, yeah, slashdot sucks when it comes to international character support.
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Consider character code 0xB5 (181 decimal) in ISO/IEC 8859-1 (micro sign).
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There is no ASCII mu. ASCII is a seven-bit encoding which only covers unadorned latin alphabetic characters, arabic digits, and some random punctuation. Even latin1 (aka ISO8859-1) lacks a mu character. I'm not sure what you think you typed, but it definitely wasn't ASCII.
There's also the problem of potential confusion between U+00B5 MICRO SIGN and U+03BC GREEK SMALL LETTER MU (among others), but neither of those is remotely ASCII.
Anyway, yeah, slashdot sucks when it comes to international character support.
ISO8859-1 (colloquially called "Extended-ASCII", "High-ASCII" or just "ASCII" even if it's ambigous since there's more than one extended ASCII character set) does have a "mu", it's 0xB5
http://en.wikipedia.org/wiki/ISO/IEC_8859-1 [wikipedia.org]
The truth is (Score:3)
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It's an archaic system that needs revising.
You don't think they don't know this already?
Of course they know it. It's just very very very hard to come up with a system that can be made independently to represent 1kG with almost no error.
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http://en.wikipedia.org/wiki/New_SI_definitions#Kilogram [wikipedia.org]
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We don't have anything better yet. Technology is yet to provide us with a way to measure anything else with more accuracy than a very carefully maintained standard weight.
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Don't we measure atoms all the time. A kilogram can just be a carbon atom (or some other stable larger molecule) times some large number.
The only thing that is not going to change mass constantly is an atom
1kg is 1 kg (Score:2)
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http://en.wikipedia.org/wiki/New_SI_definitions#Kilogram [wikipedia.org]
Water? (Score:2)
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That is many orders of magnitude less exact than the current standard.
New definition proposal (Score:2)
http://en.wikipedia.org/wiki/New_SI_definitions [wikipedia.org]
"The definition of the kilogram is undergoing a fundamental change - the current definition defines the kilogram as being the mass of the international prototype kilogram, the new definition relates it to the equivalent energy of a photon via Planck's constant.
Current definition: The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.
Proposed definition: The kilogram, kg, is the unit of mass; its magnitude is se
Oh, you mean... (Score:2)
Oh, you mean the International scientific community's attempt to redefine the Kilogram? It's called the "dildo" but they are having trouble all agreeing on the proper pronunciation. So for now they're continuing to measure up against this dildo-shaped hunk of alloy that apparently gains weight over the years and every so often has to be rubbed off ceremoniously by a skilled handler with a strap of leather dipped in alcohol.
What about the weight it's lost? (Score:2)
Hmm, conspiracy? (Score:2)
So a special interest group is pushing for the US to adopt the metric system, and now the kilogram is heavier. This means that American's weighing themselves in metric won't seem as heavy because the number will be lower therefore there will no longer be an obesity crisis in the US.
To explain it to those still on the imperial system:
It would be like currently saying you weigh 300 pounds (which is morbidly obese regardless of what the View or Oprah says), but then the standard weight of a pound increases, s
derived standard based upon volt (Score:2)
Planck's mass has been proposed too. But we dont know the unit of action to enough decimal places.
The most accurate measurement is the unit of time from atomic excitation in lasers. Thats 14 to 18 decimal places. You have to start taking account of the two kinds of relativities around the 9th decimal place etc. The volt measurement bootstraps off of this.
Physics Today
If these weights are so important. (Score:2)
They should not ever be handled, they should be in a sealed clean room.
Re:whats the problem (Score:5, Insightful)
seal it in something already, its not a desk toy. There would be no gunk if it was not exposed to it
It's kind of useless as a reference if no one can actually refer to it.
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if you know it weighed X in 2000, and it weighs Y in 2013 whats the problem
The problem is we DON'T know that. We know that the kilogram prototypes are gradually diverging in mass but we don't know which one is most correct or whether the group as a whole is gaining or losing mass. The cleaning procedures are supposed to remove contamination (and no matter how careful you are some contaimination is inevitable) without removing the actual metal of the prototype but afaict we have no real way of knowing how effectively they achieve that goal. Nor do we really know how much wear there
Re:whats the problem (Score:4, Informative)
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AFAIK, the reference kilo is already stored in a safe in a protective, inert gas atmosphere.
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As long as you can exactly count all of the atoms in a weight. Otherwise it's more useless for comparative measurement than a king's foot.
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Now you're just trading for an inaccuracy of linear measure. With a KG weight it's impossible (under any current technology) to create a perfectly geometric crystal. And with the scale needed to guarantee it's a perfectly geometric crystal it's impossible to accurately sum enough of them to make exactly a KG.
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Most silicon monocrystals are grown by the Czochralski process, in the shape of cylinders up to 2 m long and 30 cm in diameter (figure on the right)
The size of the monocrystal is not the problem.
From http://www.acpo.csiro.au/avogadro.htm [csiro.au]
The limiting factors currently are:
The variability from sample to sample of the isotopic abundances M(Si)
The content of impurities and vacancies (n)
Realisation of accurate density standards (m,V)
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This has been suggested, but it is not yet possible to do to the same accuracy as the standard kilogram.
Re:Definition (Score:5, Informative)
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-- NIST
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The meter is based on the speed of light.
You can't define a distance based on speed.
You need a well defined speed AND TIME unit.
It doesn't get any better from there...
Then zero the scale with that weight, and fill the container with absolutely pure water. The weight of that water is exactly 1 kg. No special reference needed (although you can make a reference from this).
When do you consider it "full"? Water has the nasty habit to form a spherical surface due to surface tension. Do you consider it full when the middle or the border is aligned with the "full" mark on your comtainer? And good luck getting any "absolutely pure" water that does not fall apart into ions and reforms all the time... look up the definition of ph-value. millions of hydrogen i
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You can not make water pure enough. You can't build a container cubical enough. And you can't account for the weight of your container exactly enough.
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The density of water is dependent on temperature and pressure. Pressure is defined as a unit of force per unit area (Newtons per square metre). Force is subsequently defined in terms of mass times acceleration (1 N = 1 kg * 1 m/s^2). Congratulations, you have just created a definition of mass that is dependent on itself. Also, the ability to purify water and measure its volume to a high enough accuracy and precision is extremely difficult.
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The've choosen platinum as it is already the most inert material they could find. And even if they might be less reactive, inert gases are completly out due to handling issues.
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Are these people fucking retarded?
Are the world's foremost experts on measuring "fucking retarded"?
Here's a hint: "No."
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Well actually it kind of sounds like they are. They chose a standard KG weight that would increase in mass over time at different and unmeasurable amounts, with no way to stop or reverse this.
I think that is a pretty good definition of retarded.