The Changing Definition Of 'Kilogram'

DrLudicrous writes "The NYTimes is reporting that the platinum-iridium standard mass for the kilogram is shedding at an appreciable rate -- at least compared to other reference masses. The Pt-Ir cylinder is kept in France, and measured annually, and the slight discrepancy is important because the kg is an SI base unit- thus other quantities such as the Volt are based on it. A new standard is being sought- the two frontrunners are counting the number of atoms in a perfectly spherical single crystal of silicon, and another technique uses a device known as the Watt balance."

Comments

reproducibility

[nthomas]

Although it was mentioned in the article, I think it should be emphasized that the SI definition of the kilogram, unlike their definitions of the meter and second, cannot be reproduced -- or rather, reproduced exactly. This is quite important, as it is neccessary for the standards governing body in each country to have a very precise reference weight of their own.

Since there is only one reference object for the kilogram, everything else is just a copy -- and even if it is a first generation copy, errors are bound to creep in.

The redefinition of the kg is long overdue, mad props to the scientists working on this.

Re:Kilogram?

[UniverseIsADoughnut]

" It's not a matter of dark ages, it's a matter of infrastructure... while not the largest country in the world (the US is probably third or fourth, I'm not sure), we have by far the most technological infrastructure. It is not feasible to change all that in a short period of time."

Bingo! this is why the US has been working on the process so long. Granted the push hasn't been very great but it's happening. If you're a country of a few million and only are the size of a small new england state, the change is pretty cheap and easy. When your huge, there is a massive infastructure change cost. and trying to re-wire 300 million peoples brains to a new way takes a lot more work.

I think places like Europe were also helped by war. They had to rebuild and start new with so much. So it was a perfect time to start fresh. The US is a pile of legacy ways. And nothing happens to change them.

With that said I wish we would try harder to convert. Get a dual system going now and run it for 20 years. let people adjust. Teach school in 95% SI ( only enough english units stuff so the comprehend them).

Re:Kilogram?

[SN74S181]

Perhaps we don't have the coercive state apparatus necessary to 'make' the metric system the primary system that we use.

Me, I have been doing a lot of woodworking lately. It's convenient to use a unit (the Foot) that divides easily into subunits that are multiples of both 3 and 4, without having to get all mired in floating point arithmetic.

But we have this metric flamefest every time the metric system comes up on Slashdot, and the same crap comes up every time.

I'm just happy that pointy-head metric zealots don't seem to have much pull in the real world of regular people. Keep on ranting, dudes.

Re:Kilogram?

[radish]

You do know the metric system is many hundred of years old don't you? In fact it's older than your country. The point is the US has had 200 years and they haven't even started the process. There's nothing saying you can't run in parallel - the UK has been doing so for years. It's absurd to say you have to rip out all the imperial pipes and replace them - you just have to keep 2 sets of tools around until those old pipes get replaced naturally. It really isn't hard, it's just the US can't be bothered.

Re:Volt is no longer defined by Kilogram

[vrt3]

If the volt was based on the kilogram (and therefore a relationship exists between the two), and now volt is based on frequency, isn't it possible and wouldn't it be a good idea to base the kilogram on the volt? Then we don't need those perfect references anymore.