US Objects To the Kilogram 538
Velcroman1 writes "For 130 years, the kilogram has weighed precisely one kilogram. Hasn't it? The US government isn't so sure. The precise weight of the kilogram is based on a platinum-iridium cylinder manufactured 130 years ago; it's kept in a vault in France at the International Bureau of Weights and Measures. Forty of the units were manufactured at the time, to standardize the measure of weight. But due to material degradation and the effects of quantum physics, the weight of those blocks has changed over time. That's right, the kilogram no longer weighs 1 kilogram, according to the National Institute of Standards and Technology. And it's time to move to a different standard anyway. A proposed revision would remove the final connection to that physical bit of matter, said Ambler Thompson, a NIST scientist involved in the international effort. 'We get rid of the last artifact.'"
Get rid of the artifact? (Score:4, Interesting)
Last I heard, nobody had come up with a way to define mass without referring to an artifact. It seems easy but they all turn out to be circular.
Re:Get rid of the artifact? (Score:5, Funny)
Re:Get rid of the artifact? (Score:5, Funny)
Well, you can try counting atoms. But apparently that turns out to be a royal pain.
Or at least an Imperial pain. :)
Re:Get rid of the artifact? (Score:5, Informative)
Essentially a sphere will be created of a specific isotope of silicon and a specific diameter. This sphere will have a known number of atoms. This is superior not only because of degradation of a physical standard, but also because it will be easier to create a standard from basic principles using appropriate lab equipment.
The US is quite late in it's objection as the problem has been known and accepted for many years. TIme and distance is essentially measured with light, and only the kilogram still has a physical representation.
It is probably a simple matter for the US to accept the new standard.
Re:Get rid of the artifact? (Score:5, Informative)
The Avogadro project (the thing in your link) has been going on since 2007.
The NIST (the U.S. measurements standards body) provided an implementation of another possible solution to the problem in April of 2007.
To say that the U.S. is just now objecting is inaccurate.
To say that the U.S. is late in its objection ignores the fact that the U.S. has been working on the problem with international standards bodies for many years.
What (unsurprisingly) the Fox News article gets wrong is that the NIST is not submitting a formal objection.
The Consultative Committee for Units (one of the advisory groups for CIPM), of which the NIST is a member, has submitted a formal resolution to change the definition to the CIPM. The CIPM is about to submit that resolution to the CGPM, which is the international body that regulates these definitions.
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That reminds me the last question my college roommate had on his senior oral exam. He was a physics major and was asked how he would derive Avogadro's number without the aid of certain pieces of modern technology. As I recall, his answer started with something along the lines of the following: "First, I would find a really tiny man . . . "
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The meter has already been defined in terms of the speed of light. The circle stops there.
Re:Get rid of the artifact? (Score:5, Interesting)
Aren't they just proposing removing the dependence on the 1 kilogram cylinders?
From the article:
Physicists may scoff at the thought people allowed to walk among the living who don't know what a Planck value is. But all you need to know is, they're using it to determine the mass of one mole of silicon atoms.
From there on, they'll theoretically be able to deduce a perfect kilogram and it won't have anything to do with lumps of metal ever again. /quote
Re:Get rid of the artifact? (Score:5, Funny)
title of this slashdot article should be:
Le Kilogramme is to walk the Planck. :)
http://www.theregister.co.uk/2010/10/28/official_french_kilogramme_marked_for_the_bin/ [theregister.co.uk]
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No, the new "lump of metal" will be a physical representation of the underlying definition, that being that a kg = the weight of X silicon atoms. No such precise definition exists for the current standard.
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But you know that it depends on the actual structure of the silicon crystal how much X silicon atoms weigh?
Re:Get rid of the artifact? (Score:4, Interesting)
But you know that it depends on the actual structure of the silicon crystal how much X silicon atoms weigh?
No, I don't know that at all. Please to explain.
Re:Get rid of the artifact? (Score:5, Informative)
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Ahhh, thank you, very interesting!
That said, all that means is that the reference mass will have a very slight divergence from the theoretical definition. That doesn't change the fact that the kilogram will *have* such a definition, which it currently doesn't.
Re:Get rid of the artifact? (Score:5, Informative)
The entire point of redefining the kilogram would be to allow any sufficiently-technical laboratory to make their own mass. Right now, there are forty artifacts that must be kept safe. If you do not have one of these artifacts, you in fact have no way to determine what your kilogram actually is. Hell, the artifacts probably do not even have the same mass as each other. So they are proposing to replace a few sets of metal with an instruction manual on how anyone with the right technology can make their own reference weight. That's a huge difference.
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Hell, the artifacts probably do not even have the same mass as each other.
They don't. There's variances between all the official copies which have changed over time: https://secure.wikimedia.org/wikipedia/en/wiki/File:Prototype_mass_drifts.jpg [wikimedia.org] Though technically there is only one official kilogram so even if all the others trend one direction the official answer will be that they are all wrong.
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The gram was originally defined in relation to a cubic centimetre of water (the temperature originally being 0 degrees, later 4 degrees). Then the IPK was made based on this.
So, what's the problem here? Don't we have a fixed reference, the weight of a given volume of water at a given temperature? Why can't we re-calibrate from that?
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No, because the volume depends on pressure. Which has a mass component. Circular.
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I just love ideal physics land. Unfortunately the real world doesn't work that way.
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Actually, it does. You do know that's what physics is all about, right?
Re:Get rid of the artifact? (Score:4, Insightful)
Well how frickin' accurate do you want to be?
Very, very frickin' accurate. That is the whole point.
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The Poisson ratio of water is 0.499975, which is not nearly close enough to 0.5 to be acceptable.
Re:Get rid of the artifact? (Score:5, Informative)
Ain't no such thing, or else something as basic as an electronic weigh scale wouldn't work. To rephrase: solid metals are compressible enough to measure the effect (strain) due to very reasonable external loads -- you'd think that liquids would be, too. And yes, they are.
Bulk modulus of steel, commonly strain gaged in weigh scales: ~160 GPa
Bulk modulus of water: ~2.2 GPa.
Water is on the order of 100 times more compressible than steel. Yet steel's and similar metals' compressibility (modulus) is routinely used in measurement applications!
Now to give you an idea of how compressible metals are: a soft iron sphere with a single strain gage bonded to it will give you, IIRC, 1m depth resolution if you hook it up to reasonable digital strain meter. I did the math once on Yahoo Answers somewhere, don't have the link handy.
Don't believe all they tell you in grade school for a lot of it is bullshit.
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Before I went into science, I did automation engineering (think factories with robots). A lot of that is fluid power. And any person working with hydraulics worth their salt would tell you that depending on factors, most hydraulic system fluids will compress between
So, when I took physics, and they told me that fluids aren't compressible, I objected. The instructor told me that sure, fluids change volume, but only in weird pressures like near vacuums and absurd press
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Here I have the soluition. 1 gram = the mass of 6.02x10^12 carbon=12 atoms /12 not weight since that can very with location and atmospheric conditions.
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A liter is now officially defined as 1 cubic decimeter, which makes the comparison to water only approximate.
Re:Get rid of the artifact? (Score:5, Interesting)
Nah, it's actually pretty easy. You say something like "one kilogram is the mass equivalent of the energy of 3.40812408 gazillion photons with a wavelength of 550.9466543 nanometers." The meter is already defined in terms of speed of light and the second, and the second is defined in terms of the natural frequency of the caesium-133 atom. So in the end, everything is defined in terms of the speed of light and the caesium atom, with no artifacts needed.
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If counting and weighing photons were so easy... you'd have a point. But it isn't. Pretty much every proposal for replacing the kilogram standard so far has either ended up in a circular definition, or required us to do something we don't actually know how to do.
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easy, it is how many weight exactly one kilogram
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Um, the electron-volt(eV)?
I suppose you could use a reference electron, but any old electron will do.
Re:Get rid of the artifact? (Score:5, Funny)
No. The reference electrons are specially-calibrated in the lab to meet the exacting standards of the measurements industry. If you start using sub-standard electrons, you get sub-standard measurements.
I have personally seen the effects of creating matter using electrons with a charge of -0.93 instead of the usual -1. The matter that we were shipping had a net positive charge, so we had to include EXTRA electrons in the order so that the USP guy what not fatally electrocuted when he picked up the box. Do you have any idea how much those extra electrons cost my company?
Please do not even get me started about cut-rate protons. What happens when heavy water is not quite so heavy? You don't even want to know.
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There are several ways to define a KG using constants or atomic weights. http://en.wikipedia.org/wiki/Kilogram#Proposed_future_definitions [wikipedia.org]
The trick is that you not only have to be able to define it, but measure it reliably and accurately.
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The artifact system is not reliable and accurate, and certainly not easy to use. If you can't replicate the conditions of the definition in a remote lab, then the definition is bollocks. I mean, what if we lose these things?
The right way to do this is to reverse the definition of Avogadro's number. Instead of "Avogadro's number is the number of C-12 atoms in 12 grams of C-12," you say "Avogadro's number is exactly 6.022141500000000000000000x10^24 and that number of C-12 atoms is 12 grams."
Now anyone who
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You could use an integer number of some base element (hydrogen, helium, carbon 12 something like that). Sort of like time based on radiation emissions or the like. The problem is both precisely and accurately measuring it, and agreeing on what base element. The actual details are fairly simple, you probably want something with the minimum of unstable isotopes that occur in the minimum quantities possible. It's a matter then of finding something suitable (that you can either separate out the isotope easi
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The goal is to use a single atom as the artifact. Atoms (of a specific isotope) are always *exactly* the same, so there's no concern about variations in the weight of the artifact over time.
So all you've got to do is build an object with a mass as close to 1 kilogram as possible, precisely count the number of atoms it contains, and then make a definition like:
"A Kilogram is defined as the mass of 5.018451 x 10^22 atoms of Carbon 12".
The difficulty is precisely counting the number of atoms in a macroscopic
Re:Get rid of the artifact? (Score:5, Interesting)
Last I heard, nobody had come up with a way to define mass without referring to an artifact. It seems easy but they all turn out to be circular.
kilogram: the amount of mass required to deflect a proton by X degrees at a distance of Y meters.
I'm guessing X and/or Y would have to be quite small.
Re:Get rid of the artifact? (Score:5, Insightful)
The point is that the definition needs to be practical. We need to have a way to actually measure a kilogram using the definition, so we can calibrate our scales. If we can not use the definition to calibrate a scale to some very high accuracy, it is useless.
Question... (Score:3, Funny)
How does "America" define the pound...?
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international avoirdupois pound [wikipedia.org] is set to exactly 0.45359237 kilograms... or is it? I guess that's why the US cares if the kilogram loses weight.
BASE16 (Score:5, Funny)
Ounces and pounds were way a head of the time and are becoming even more useful with the advent of computer systems and the common use of base16.
16 ounces in a Pound is not just coincidence.
F=15 ounces
10 = a pound
We can all agree, I am sure, it's easier to look at 89 and go, 8 pounds 9 ounces. With metric I have to keep moving the decimal place around and remember how many 0s there were in huge words like kilogram, milligram, centigram.
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Computers use base 2, humans use base 10.
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You're almost right. Base 16 (hexadecimal) happens to be a convenient way for humans to do base 2 math. Any programmer worth his salt can do hex math in his head. ;)
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Re:BASE16 (Score:4, Funny)
Clearly you don't expect people to do hexadecimal floaing point calculations in their head?!
No, Mr. Bond, I expect you to 0xD1E!
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ha ha space cadet
they are the same thing
silly human
That was almost a haiku (Score:3, Funny)
ha ha space cadet
they are the same thing
silly human
Here's one that scans better:
ha ha space cadet
they are the same frelling thing
you silly human
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Yes, but 16 is easier to carve up into smaller pieces using fractions.
10 is divisible by itself, 5, 2, and 1.
16 is divisible by itself, 8, 4, 2, and 1
12 is even better than 16
12 is divisble by itself, 6, 4, 3, 2, and 1
.
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CPUs use base 2 and many Computer "Systems" use base 16.
I'm human and I use base 8. Worked in a knife sharpening factory as a kid. :(
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All bases are base 10
Whoosh! (Score:2)
Obviously base16 would be retardedly hard for every day measure for most people.
How many pounds is FCA again grandma?
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> ...we still insist on using the pound over the kilogram.
But we don't. The metric system has been legal for trade in the USA since 1866 and the official customary units have been based on it for almost as long. In 1975 it was official adopted by the Federal government for its use and in 1985 it was identified as the "preferred" system for trade. Most goods are labeled in both metric and customary units. It's just that, unlike other countries, the USA has not outlawed the use of customary units as we
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Sure. Please do the following calculation in your head (you can use your fingers too)
Let's say a bag of wood weighs 8 pound 9 ounces, and you want to buy 3 bags. What is the total weight in pound and ounces?
Versus, you have 8.9kg of wood, and you want to buy 3 bags, what is the total weight in kg?
I am sure you'd be able to multiply in BASE16 if you are trained for it, and memorize the BASE16 multiplication table when you were a kid. But for the rest of us, BASE10 is what we learned and used to.
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By posting the same thing anonymously.
Did the OP even read the NIST doc? (Score:5, Informative)
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old, and not just the US (Score:5, Interesting)
seriously, this is pretty old. physicists working in metrology have been working to redefine the kilogram for at least the last few decades
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Metrology? Heretic! It's Standardology. Don't be trusting no metric.
Best of Both Worlds (Score:4, Funny)
We have American pints and British pints; the imperial tone, the short ton, and the tonne; why not have an American kilogram and traditional kilogram as well? That should really simplify things for NASA/EUA coordination.
Re:Best of Both Worlds (Score:5, Funny)
That's it! Define a kilogram in terms of pints. Now, the quandary: ale or lager?
It makes as much sense to define a kilogram as some huge number of moles of banana pudding or something like that.
Re:Best of Both Worlds (Score:5, Funny)
Wouldn't a mole made out of banana pudding degrade pretty quickly itself?
And how could it burrow?
Solution fail. Tasty, tasty solution fail...
Speaking as a metric man (Score:4, Interesting)
Funnily enough I never ever think of a kilogram as the weight of some standard weight in a vault somewhere. The only way I ever think about the kilogram is the weight of one liter of water. Also comes in handy when I'm calculating how much liquids I can afford to buy when shopping groceries, given that I often go to the store on foot for the exercise and have to make sure I can manage the haul back.
So, um, does this all really matter? In practice, that is.
Re:Speaking as a metric man (Score:5, Funny)
then how do you define a liter?
OH I JUST BLEW YOUR MIND
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litre
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Why the amount of water that weighs 1kg of course!
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It's the amount that fits into a cube that has a side equal to N wavelengths of light from the relaxation transition of atom X.
Oh I just stepped on your dick!
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http://en.wikipedia.org/wiki/Properties_of_water#Density_of_water_and_ice [wikipedia.org]
good luck measuring that to any degree of accuracy beyond three or four decimal places. just because you know how much of something you SHOULD have, does not mean you know how much you DO have.
Who cares? (Score:5, Funny)
That being said, keep your filthy hands off my hogshead.
Re:Who cares? (Score:5, Funny)
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You totally stole my comment. Or saved me the effort. Or whatever.
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If you're dealing in kilos rather than grams, I think you can hire people to figure it out. So do what you will with the kilogram - just don't change the gram, and we're all good!
Re:Who cares? (Score:5, Insightful)
It's true... (Score:5, Funny)
I'm not even sure we even use Imperial units anymore...
From reading the news, I believe our units are:
- Hairs
- Stories
- Football Fields
- Libraries of Congress
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Please, it's used i a lot of places. My kids learn metric in grade school. In fact, just the other day my son referred to a distance a centimeters. in casual conversation.
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In fact, just the other day my son referred to a distance a centimeters. in casual conversation.
And some kid didn't come out of the bushes, punch him, call him a nerd, and run off?
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The difficulty of standard artifacts (Score:5, Funny)
"There is one thing of which one can say neither that it is one metre long, nor that it is not one metre long, and that is the standard metre in Paris." - Wittgenstein, Philosophical Investigations
Re:The difficulty of standard artifacts (Score:5, Interesting)
Very clever, Mr. Wittgenstein. Unfortunately shortly after you died we defined the meter in terms of the speed light travels in a certain amount of time, and abandoned the Paris standard meter. So one thing can be said for sure: the Paris standard meter is definitely *NOT* one meter long."
I suspect that all the fuss... (Score:2, Insightful)
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No, but every NIST-traceable instrument eventually gets back to those standards. Sure, there are a very small number (probably a dozen or so) weights directly calibrated against the original articles. But then those are used to calibrate a few hundred weights at metrology labs, which are used to calibrate weights for thousands of customers around the world. Each step introduces uncertainty, but uncertainty around a precise value can be accounted for. Uncertainty around the wrong value renders the instru
No more gold standard (Score:5, Funny)
We're going to let the kilogram "float" and put it on the commodities market. It should triple the value of the gram
Re:No more gold standard (Score:5, Funny)
Fractional Reserve Physics FTW!
Say what? (Score:2)
Why is the US objecting to a standard that it has not ever taken the time to actually use? Talk about anything in metric to most anyone from the US and they go "what's that in English?" Argh!!!!
That said, I am compelled to agree with the reasons for the change... hopefully the new value is close enough to the old that not too much should require updating (I'm thinking the most likely candidates for updates are books in astrophysics).
I wonder why american scientists care (Score:2)
...given the bulk of the population doesn't even know what metric is and that they measure distances in football field lengths.
Not quite as retarded as calculating weight in stones, but it`s only a foot away from that.
Kilogram is a mass not a weight (Score:5, Informative)
Newton is a weight. The summary (and the Fox article) are incorrect, while the NIST article correctly refers to the reference mass.
MJC
Re:Kilogram is a mass not a weight (Score:4, Funny)
No, a Newton not a weight, it is a cookie.
https://secure.wikimedia.org/wikipedia/en/wiki/Fig_Newton [wikimedia.org]
And too many Newtons leads to weight gain.
--
BMO
Headline is sensationalist (Score:5, Informative)
and misses the point. The variability of the kilogram standard is a scientific and engineering concern, not a political one.
Wikipedia discusses the issue: http://en.wikipedia.org/wiki/Kilogram#Proposed_future_definitions [wikipedia.org]
In a nutshell - in order to create 1 kilogram physical standard masses, you have to first know what a kilogram IS. The physical standards referred to in the article do not appear to have retained constant mass over time. You can't define a constant based on something that is variable, so the current masses are (as I understand it) acknowledged to be an inadequate basis for the definition of the unit. The problem arises when you try to pick something to define it with that is both stable (i.e. a fundamental property of the natural laws of the universe) and practical (can actually create one to use as a practical mass standard against which you can prepare working standards.)
From articles that have popped up about this over the years, my guess is they will have to pick something as a basis and then work on various practical techniques to get as close to that ideal as possible - the question is what specifically to pick. N Carbon atoms? N Si atoms? What are the pros and cons when trying to physically create something that represents those numbers? How stable will a standard created according to a chosen standard be over time? (I.e., how often to we have to make new master standards? It's an important question - obviously the existing masses were not chosen with the expectation that their mass would vary with time, so how do we know to trust a given solution?)
So it's not the US objecting to the kilogram as a unit, but rather concern over the methods used to DEFINE the unit. That's something quite rational, not specific to the USA, and of scientific interest. Editors, how about changing the title to "US to Propose New Method of Defining a Standard Kilogram" instead?
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This is Fox News. From their perspective, *all* concerns are political concerns.
Global warming, economic policy, genetic engineering, epidemiology: all of these are relevant to Fox News (and MSNBC etc) only for their impact on the great battle between conservatism and liberalism.
Ben Franklin & precision (Score:3, Interesting)
Oddly enough, back in about 1780, the US was desperate to switch to the new metric standard that was being developed by France.
The reason why the US didn't go for it was the definition of the metre. Benjamin Franklin, who was a pretty good scientist when he wasn't being distracted by all this political nonsense, was unhappy with the French definition, which was a certain ratio of the Earth's circumference. The trouble with this is that not only is it practically unmeasurable, but it's not even a knowable value, as it changes depending on what you consider to be the Earth's surface. Franklin was aware that industry can always use as much precision as it can get. Events bore him out as the first metre artifact made turned out to be out by 0.2mm.
Instead he advocated an alternate definition based on the swing of a pendulum of a fixed period. This was a knowable value; it could be theoretically calculated to as much precision as your definition of the second. As the second was at the time was based on the length of the average solar day it could be determined as precisely as you could build your telescopes, it was a much more useful definition.
Unfortunately for complicated political reasons France was unwilling to go with this (possibly because their arch enemies, the British, were also considering a pendulum-based definition), so Franklin decided to stay with home-grown units rather than adopting the new metric system.
So if Franklin had been just a little bit more convincing when addressing the committees in Paris, the US might have been one of the driving forces of metricisation, and maybe my web browser would have the word 'metre' in its spellchecker dictionary.
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we were very close to converting. Reagan killed that, because he need to make it look like he was cutting spending. Fucking douche.
Thanks, but no thanks. (Score:3, Insightful)
Re:Weight a minute... (Score:5, Interesting)
Because this prototypical kilogram is what the definition of the pound is currently based on.
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The US cares that much why? Its only a trade matter, as we still use primitave imperial measurements. Maybe if we had switched to metric like they had told us we were going to every year in grade school this would be a big deal, but right now, who cares?
Because prices, taxes, tariffs, etc. care about pounds and kilograms. We still have a department of weights and measures, and they still do extremely important work. The fact that you don't ever notice any problems means they're doing their jobs.
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The US was one of the original signatories to the treaty that defined the meter and started the BIPM which lead to the SI.
All US weights and measures, no matter what standard they are on, come from the National Bureau of Standards which standardized on the metric system, as has the USGS (since the early 19th century).
THe NBS has standard meter and kilograms that are copies of the originals kept in Paris, so the US has a valid reason to wonder about the new kilogram definition.
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Ugh. I teach college intro physics, and even *I* think that's a sociopathically pedantic distinction.
In my class, I'm happy to use "an object weighs 5 kilograms" to describe the mass of something. I'm just careful to call the gravitational force on the object the "gravitational force", and never the "weight".
It's all clear and consistent unless you try to use the Imperial system, in which the pound is a unit of force. So I don't.
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Second, I don't care what the experts say, a kilogram is equal to the mass of one litre of water, which is equal to 1000 cubic centimetres of water, or a 10cm x 10cm x 10cm box full of water.
Does it have to be pure water, or can it have some impurities in it? What temperature is the water? What pressure? When you're trying to do especially delicate measurements, these details matter!
The "weight of a liter of water" will continue to be the useful informal definition, but we need something more precise fo
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I don't think so. One of the goals of the metric system over the past century has been to find ways to define the units in terms of fundamental physical constants, as opposed to something completely arbitrary like creating a block of some material and saying "this block is a kilogram". The definitions, by nature are still going to be somewhat arbitrary, but at least once you make the arbitrary definition based on a physical constant, it's easy to reproduce. We could explain to an alien 1/2 way across the ga