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.
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
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.)
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.