Slashdot Mirror
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
A kilogram is a unit of mass not weight. Weight is dependant on gravity. Mass is not.
You're using her as bait, Master!
(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.
that wouldn't work - after all, then you've just scaled the problem down to ask "whats the weight of a proton"
remember that the base physical units have to be directly related not to theor, but to empirical observation. That's the difference between "units" and "physical quantities"
MASS is a physical quantity. "kilogram" is a "unit" of that quantity. defining it in terms of the "mass of a proton" makes no sense because thats essentially a *circular* argument.
if you;re gonna construct a vast edifice of science, the foundation better be damn rigorous! this isnt just semantics, its essential, the way that we have to be absolutely sure that 2 + 2 = 4 (which can be derived from the Completeness property of the Real number Set). A good reference for basic units and quantities is here.
Don't blame me - I voted for Howard Dean. http://dean2004.blogspot.com
If there isn't, then you're way smarter than most practicing physicists... gravity is hard.
The Mongrel Dogs Who Teach
Do you know how many states of water there are? Not to mention somewhere you are going to have to define a pressure, a temperature etc. You don't exactly want to end up with a circular reference in there....
Now, at CSIRO, they are researching into using a super spherical ball of silicon, about 8 cm across, and weighing 1kg. It is spherical to an accuracy of 8nm, and was built by the same glass grinders that build lenses for our precision instruments and telescopes. We have shipped one or two overseas (and have one or two in .au), so that people around the world can test 'em.
Pretty cool in all - I watched the guy pick it up with cottonwool, in the same room that I was in - no contaminant free clothes, either - it is pretty robust. It is all part of an international effort to produce new standards of mass etc - the platinum bar in Paris is getting a bit old. IIRC - CSIRO are researching another method, but can't remeber what it was....
You could even define it as the energy in some huge number of photons of a particular wavelength. :-)
Hmmm - which unfortunately comes back to a density of photons, and a length cubed, which unforteunalty comes back to that damn platinum bar in Paris. IIRC - it has a chip in the corner of it too - Ooops. I just dropped your metre - my, how you have just grown!
A gram is not a measurment of weight.
...
It's a measurement of THC
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.)
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.
why, exactly, a kilogram [...] never weighs the same twice? MouseR
Presumably, because of engineering imperfections in the (mechanical) measurement devices, and perhaps also due to local variations in gravity, caused by tectonic forces, tides, etc.
The bottom line is: weighing a physical chunk of metal is as poor a standard as measuring the length of a chunk of metal. We do better if we can relate these standards to invariant values derived from basic physics.
-- We all have enough strength to endure the misfortunes of other people. La Rochefoucauld
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.
"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...
- Entertaining Bits from the Ancient Kernel Tree
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.
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.