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NIST Wants An Electronic Kilogram
Dearing writes "According to the Global Engineering Journal, NIST, those not-so-standard standards people, want to give up the hunk of metal they've been calling a kilogram, even though it never weighs the same twice. In it's place, an electronic kilogram could act as the permanent standard."
We all now lost 10% of our weight. I just hacked NIST's computers and changed the reference.
Why aren't I thin now? I must hack the electronic tape measure next.
$10 if you want me to make you taller, too.
Why when I was a lad, all we had was a platinum-iridium cylinder, and we liked it. But you damn kids today, with yer newfangled electronic kilogram, why I oughta...
They balance it against gravity to measure it? Wouldn't that be really, really inaccurate, since gravity varies by altitude, local density variations, etc? Did I misunderstand what I just read?
Sheeze, why not just define it as 1.498e20 atoms of carbon (or whatever number), and be done with it.
Sometimes it's best to just let stupid people be stupid.
NetInfo connection failed for server 127.0.0.1/local
hunk of metal they've been calling a kilogram, even though it never weighs the same twice.
A gram is not a measurment of weight.
A kilogram is a unit of mass not weight. Weight is dependant on gravity. Mass is not.
You're using her as bait, Master!
You could define a kilogram as the amount of water in a cubic decimeter. Or, you could define it as the mass of 6.02 * 10^23 protons, or any number of other ways. I don't understand how this measurement they intend to make with the device they have will be any more accurate or easier to deal with.
You could even define it as the energy in some huge number of photons of a particular wavelength. :-)
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(one of) NIST's own web page(s) on this is at http://www.eeel.nist.gov/811/elec-kilo.html. There's a lot more technical detail there than at the link given in the article.
This really does make sense to replace the artifact with something independent -- they have a bunch of "voodoo" every time they measure the current kilo to try to get the same answer.
Call me a computer scientist, but isn't there something recursive about defining the prototype kilogram with gravity and then measuring gravity at the same time?
There are ways of measuring gravity without a known mass standard. For example, you could measure the acceleration of an object falling freely in a vacuum chamber (only need length and time measurements).
However, it does seem strange to me that they'd base the kilogram standard on something as indirect as the local gravitational field.
If there isn't, then you're way smarter than most practicing physicists... gravity is hard.
The Mongrel Dogs Who Teach
yes.
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Of course, you'd need more than the amp. There are a bunch (seven?) of fundamental constants, out of which all other units can be made. You'd need them all, and to communicate them, you'd need experiments that determine their value. So far, we have no such procedure for mass... so we couldn't calibrate the masses in the experiments.
It's not that the aliens are stupid. It's that we don't yet know how to communicate the value of a mass independent of a reference mass.
Oh, and by the way: The late doctor never said the aliens had space travel. Indeed, he implied the opposite: If we had to communicate from afar... using, I suppose, EM waves.
The Mongrel Dogs Who Teach
In reality, I'm sure we could at least replace it with a theoretical definition that's more accurate than the cylinder. Even though the current definition of the meter is physical, in practice it's difficult to measure (the distance light travels in 1/299,792,458 of a second).
So, define the kilogram as the amount of mass that one liter of pure water contains at 4C. We already know the definitions of the meter exactly (defined by scientists, thanks very much), electric field permittivity (\epsilon_0), magnetic field permeability (\mu_0), the speed of light (c), etc.
With all these constants defined exactly, it just seems like there would be a better way...
They're using the current(physical) standard to establish the new(elctronic) standard.
The new standard is going to be "the ammount of mass properly balanced by XXX volts and YYY amperes in the referenced system." That ammount is expected to be more consistent than "the ammount of mass needed to properly balance that hunk of metal we have in the basement."
The current (physical) standard changes from time to time due to dust, wear(from cleaning), etc.
Do not confuse duty with what other people expect of you; they are utterly different.Duty is a debt you owe to yourself.
Time to open up your math books, sonny. You are right, in that gravity, G, is a function of masses, m and M, BUT mass is NOT a function of G!
G=f(m,M)
M!=f(G)
Therefore, mass doesn't need to have anything to do with gravity, but gravity cannot exist without mass.
Furthermore, you cannot realistical measure the mass of earth at any given time to the precision required by any lucid standards committee (especially when you using that value without a standard measure of mass to begin with), nor can you realistical the distances between object centres.
"Don't mind me cutting myself on Occam's Razor"
So now if I want to buy a kilo of cocaine, some dealer's gonna have to walk up to some two story tall machine and poor in the coke until it's 1 kilogram?
This should be GREAT for police officers. Just look for two story tall electronic kilogram machines to bust all the coke dealers.
mp3's are only for those with bad memories
Tis no flamebait (Tis a remorseless eating machine)
Jack Valenti and the MPAA are to technology as the Boston strangler is to the woman home alone
why, exactly, a kilogram [...] never weighs the same twice?
IIRC the idea is to convert the standard of mass to a number of electrons accelerated by some well known voltage.
The electrons since they are moving, produce a magnetic field which pushes against a well known reference magnetic field (which can be measured without concern for mass). This magnetic repulsion is used to balance a 1 kg reference mass against gravity.
Since gravity produces acceleration independant of mass (ma=F=mg => a=g), it's also possible to measure the local gravity to a high precision by means of the acceleration with needing to know something's mass.
Thus we have a way define mass in terms of a number of electrons (and a geometry of the path they take, technically) and other measured quantities which don't use mass in their standards.
You could say mass is so many atoms of some reference substance, but how do you measure it? Since you can't first weigh it and extrapolate from there. Similarly volume would depend on temperature, structural arrangement, and other things. The people at NIST claim this provides a more easily reproducible method of defining mass. (Of course I'd rather just stick with the electronic scale or balance pan since these tend to be accurate enough for me.)
to a high degree is that they've been adjusted
to match the a weight that's been adjusted to
match a weight that's been adjusted to match the
standard kilogram... Or something like that - I don't remember how many intermediaries would be
between the standard kilogram and a commercial
weight.
Anyway, the "standard techniques" for determining
the mass involves the standard kilogram at some
point (even for the US, as the US officially defines all it's measurements using SI units).
They can send it to me. It would make a nice paperweight and conversation piece, don't you think? And not just because of the value of the precious metals.
"The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second" (17th CGPM, 1983, Resolution 1)
While the kilogram is still defined as:
"The kilogram is the unit of mass: it is equal to the mass of the international prototype of the kilogram" 3rd CGPM (1901)
Friends don't help friends install M$ junk.
Yes, but of the SI units, only the kilogram is defined in terms of a physical artifact instead of a textual description of a measurable natural phenomenon.
Second: The second is 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 cesium 133 atom.
As mass and energy are equivalent, can't they just define the mass as a certain number of barrels of that cesium 133 light? Right now they just throw away that light each second, but they could recycle it.
Not "want to give up the hunk of metal...even though it never weighs the same twice", but "they've been calling a kilogram, even though it never weighs the same twice."
This next song is very sad. Please clap along. -- Robin Zander
..an electronic kilogram...
Sorry, the acronym EKG is already taken. Please try again.
I like to play children's songs in minor keys.
"We're all sons of bitches now." --J. Robert Oppenheimer
...just like economists talk about the 1974 dollar as being a standard to refer to (when discussing values from different years, to account for inflation) I guess scientists will start having to use "dated kilograms".
For example: "Pluto masses 1.203e12 Kg? Is that in 1993 or 2001 kilograms?"
That would be defining 'mass', not 'weight'.
The problem is a practical one; they are trying to find an easier way to take something, and determine if it is a 'kilogram' or not.
Balancing it against a reference weight is one way.
What they are saying is, doing this electronically is more accurate and easier, using magnetic fields and measured currents and such rather than a classical balance.
The definition of a kilogram of mass isn't going to change. They're just finding a better way to measure it.
That's odd, I don't understand how this question relates to an article about an electronic standard for mass. And before you flame me for nitpicking, let me remind you that Mars has some very expensive upper-atmospheric dust right now thanks to imprecise communication about units of force. Ordinary people can blithely confuse mass and weight without causing problems. Engineers can't, and this article appears in an engineering publication. When are we going to learn to be more precise about this sort of thing?
When all you have is a hammer, everything looks like a skull.
The ultimate goal is to derive all measures from
the fundamental constants of physics.
The two most popular are "c" the special of light
and "h" Planck's quantum of action.
A recent Physics today suggests a using
E=mc^2 and E=hv, where v is a frequency.
Frequencies are the most accurately measurable
item in the universe, at a current accuracy of
one part in 10^19. So the proposal is to choose
a "kilogram frequency" that precisely defines
the kilogram. There is already a "meter frequency"
that precisely defines the meter length in terms
of light velocity. And a "second frequency"
which some frequency count close to an astronomical
second.
The least well-known constant is the gravitational
constant, measured only to four decimal places.
The probably is instrumental error, because
everything pulls on everything else.
At least twice in the past decade someone has
proposed changing the law of gravitation because
of funny measurements, but every time an
experiment error was found. The constant "G"
doesn't fit into many physics equations,
so it isn't as easy to bootstrap equations
as for the other constants and measurement units.
Weight is an acceleration experienced by objects with mass due to their attraction to other objects with mass. There is arguably no point on the entire Earth where there are no lava currents, continental drift deviations, or other disturbances that could change the amount of mass under need your feet, which would directly change the amount of gravity you experience, and therefore your weight.
Dewey, what part of this looks like authorities should be involved?
"NIST, those not-so-standard standards people, want to give up the hunk of metal they've been calling a kilogram, even though it never weighs the same twice."
of course it weighs different every time, it's a standard kilogram, which is a measure of mass. the weight of the Kg will differ as gravity differs - which is a fun little trick having to do with the mass of the earth and the nearby celestial bodies.
the whole point of the new measuring device is (basically) to more accurately measure the force of gravity on the standard mass - by doing some magic with a magnet keeping the whole thing in balance. this is really just getting at a better measurement of gravity than anything else.
the crux of the situation is that the only standard for a kilogram is the actual lump of platinum itself. other things, like the standard second, are based on fun stuff like exactly how many times a cesium atom vibrates at a particular temperature. it might be fun to try and define a kilogram as Exactly This Many platinum atoms and be done with it, but that's kinda tricky for the moment.
it might be a better "standard" to accelerate the "standard" mass at a "standard" rate and measure the forces. say, by swinging the thing around in a calibrated centrifuge at whatever we're calling one Gee. then you can get to the bottom of the whole "weight" issue (in terms of newtons, i suppose).
besides, unless the standard mass is made of something that's decaying (radioactively - it's not like they'd make the thing out of, say, beef), it'll be pretty much the same mass for quite some time. it's just those nitpickety scientists at the NIST (on which i read a very interesting article recently, i believe in National Geographic Magazine) who want it to be defined in terms of something that will never change
and secondly, since when is the NIST "not-so-standard"? they are the national frickin' institution for the damned things, so they should be an authority on the subject...
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Gimme SI any day!
And Taco, WTF is the "postersubj compression filter?" Why can't you just explain in plain English what the fuck you do or do not like in the comment boxes?
It doesn't mean much now, it's built for the future.
The new standard is going to be "the ammount of mass properly balanced by XXX volts and YYY amperes in the referenced system."
SI standards based on absolute numbers (as opposed to chunks of metal) include the second (9192631770 ticks of a cesium atom) and the meter (the distance light travels in 1/299792458 second). But you can't define kilogram in terms of volt or ampere because they're already based on the kilogram. A volt is one watt per ampere. A watt will raise a 1N weight at 1m/s, while a newton will accelerate a 1kg mass at 1m/s^2. An ampere is the current in two parallel wires 1m apart that produces 2e-7N per meter of length. Therefore, defining a kilogram in terms of a volt or ampere would be circular (unless NIST skillfully arranges the equation to solve for kg); NIST must define its new version of the kilogram in terms of the second and meter.
Sources include NIST's current definitions.
Will I retire or break 10K?
well, yeah, but you'd run into the same problem of accuracy in the measuring device, in this example: friction.
though your second example (the vacuum) makes slightly more sense, it still relies on gravity, which is just slightly variable enough that it's going to be a different measurement every time.
so, back to where we started...
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There's a guy on the corner what can measure out quarter and half ounces with amazing consistancy... dunno why they have to go to all that trouble, when they could hire this guy cheaper.
Betcha if scientists were wont to shoot NIST people if their measurement vehicle was wonky because NIST's dumbell was off, you'd see some pretty accurate measuring going on over there...
Potato chips are a by-yourself food.
i suppose, because after all, E=Mc^2
making the actual measure of a kilogram's worth of energy, tho, would be quite messy and would likely result in the destruction of the testing apparatus, as well as the planet upon which it sat.
- Entertaining Bits from the Ancient Kernel Tree
Similarly, the kg could be defined as "the mass of 4.32415234895 x 10^33 protons (or whatever -- pulled that number out of you know where).
How is one supposed to accurately count 4x10^33 protons without allowing them to be bound into an atom (which decreases/increases the mass).
ok then your [sic] infringing on my copyright! Could you as [sic] me next time before STEALING my comments for your own?
This reminds me of when a previous physical-object based basic measurement standard was updated, the meter. Instead of being "one/ten-millionth of the distance from the equator to the north pole along a meridian through Paris" (http://www.surveyhistory.org/the_standard_meter.h tm), the measure was eventually (after a couple of rounds of revisions) standardized to be the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock.
When people asked if it was the measurement that was being changed, the answer was no, just the precision and accuracy that we can replicate the measurement.
Same goes here, the sea-level weight of 1 kg of mass is not being changed, just its precision and accuracy.
sarchasm: The gulf between the author of sarcastic wit and the person who doesn't get it.
Let's see. 6.022 x 10^23 Carbon-12 atoms (approximately) to 12 grams, so about 5.018 x 10^25 Carbon-12 atoms to a kilogram. Start counting, and don't let me catch you letting a couple Carbon 14 atoms slip in!
We could easily define the kilogram by the number of Carbon-12 atoms it should contain, but then it would be a real pain to figure out if something weighed a kilogram to any great degree of accuracy.
~~~~~~
under-paid karma whore
sure we can define a Kg as X number of X element's atoms. but we cannot use that standard. (How exactly do you count out X number of atoms?) what they are trying to do is make a standard that is actually useable. The standard for time and length are actually useable. the standard for volume is actually useable. the standard for mass is not useable and has needed a replacement for decades.
Do not look at laser with remaining good eye.
These are the wanks who own the government contract to extort hundreds of dollars from anyone wishing a copy of a standard developed by the government.
They get rich selling the public its own property.
They can go pound sand.
--Blair
"NIST, on the other hand, is a national treasure."
My main point was regarding the feasibility of using that as a reference. Transitions of cesium atoms or whatever the second uses is easy to measure using an atomic clock.
In any case, we already have a similar definition. "The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12." I guess it would be sufficient to simply pick a particular fixed number near 6.02x10^23 to be exactly equal to a mole.
ok then your [sic] infringing on my copyright! Could you as [sic] me next time before STEALING my comments for your own?
the "mole" is a CONSTANT which is a separate animal entirely from "units" and "quantities"
your analogy is flawed... constants are hybrid entities which in the end must be defined in terms of a unit. that's why the definition for mole is "some integer related to the definition of a kilogram"
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For example, you could measure the acceleration of an object falling freely in a vacuum chamber (only need length and time measurements).
Only if you know your exact distance from the earth's center (as well as the earth's mass). How do you determine that? To measure G you need to use a torsion balance, and that requires a definition of kg (since G is defined in terms of N*m^2/kg^2).
ok then your [sic] infringing on my copyright! Could you as [sic] me next time before STEALING my comments for your own?
Only if you know your exact distance from the earth's center (as well as the earth's mass). How do you determine that? To measure G you need to use a torsion balance, and that requires a definition of kg (since G is defined in terms of N*m^2/kg^2).
From the description of the device, it relates the mass of the standard kilogram to an electromagnetic force, by balancing that electromagnetic force against the gravitational force on the mass (== the weight of the mass).
Therefore, the only relevant parameter is the one relating the mass of an object to the gravitational force on that object. This is "little g", the local gravitational acceleration, and it can be measured directly with only a length and a time standard. You don't need to know "big G" or anything about the earth.
The gravitational force on an object is given by:
Force(N) = mass(kg) * g(N/kg)
(note that 1 N/kg == 1 m/(s^2))
nickels, dimes and quarters are accepted units for such things.
What we call folk wisdom is often no more than a kind of expedient stupidity.-Edward Abbey
You are right, I should have said Coulomb which is charge which is what I really meant. (It has been a while since physics.)The flaw in your calculation is that we don't want kg to cancel. So, if you changed amperes to Coulomb/s which is the real definition.
Then, volt = kg*m^2/s^3 per Q/s
Then, kg = volt*s^2*Q/m^2
So, as long as you have another standard for volt based on charge and time and the speed of light. Then, all measuring devices could be referenced against a charge standard and time standard.
Does that work?