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."
A kilogram is a unit of mass not weight. Weight is dependant on gravity. Mass is not.
You're using her as bait, Master!
Doesn't look like they've replaced the hunk of metal, they've replaced the balance scale.
No, they are just trying to make sure that the new mathematically "electrically" defined kilogram is as close as possible to the current kilogram.
The same way they redefined a second based on a certain number of rotations of a cesium atom (or something like that) and redefined a meter in terms of light-seconds. They got the new definitions as close as possible to their old values.
This is nothing more than doing essentially the same thing with the meter, however more difficult.
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...
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.)
Sigh... Reading these responses fills me with doubt about the future of computers in general since half the people posting are posting with ignorance of the simplest physics concepts that should have been learned in Grade 10 science class. Maybe these posters are drop outs? Or maybe they think they are hot IT people because they installed linux a few times?
I predict that software design (open source and closed source) will decline further as too many unknowingly ignorant people make decisions. More crashes, more bad designs, more strange problems.
You are on your way to becoming a Pointy Haired Programmer!!! Stop and question yourself before you post!!!!
I'd say this is the poster child of proper moderation... First post gets +5 funny, second gets +5 funny, third gets 1,redundant. This is honestly the best moderation I've ever seen here and I say all moderators take a look at this and take note.
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.
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.
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?