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Kilogram Reference Losing Weight
doubleacr writes "Ran across a story on CNN that says the "118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight — if ever so slightly. Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.""
It's not losing weight, it's losing mass!. The kilogram is not a measure of weight, but mass. Silly pound-centric editors :p
I thought that originally the kilogram was defined in terms of water, the mass of 10 square cm of water.
We can't use water as a reference since the molecules in the water are constantly splitting into ions and reforming as molecules. So it is essentially impossible to get 1000 cm^3 of "pure" water. It will be some mixture of H2O, H+ and O-- ions. Also, it would be incredibly hard to prevent other molecules from being disolved in the water. A few stray molecules hitting the surface will ruin your reference mass. Not to mention you need a container to keep it in...
The meter is defined in terms of the speed of light so that gives an empirical way to define the kg independent of anything else.
As mentioned above, we could measure a 1000 cm^3 volume, but we couldn't guarantee the purity of the water in that volume.
That's one reason we are trying to make a perfect sphere to replace the reference kilogram. Then we will have a definition of the kilogram in terms of number of silicon atoms.
Reading code is like reading the dictionary - you have to read half of it before you can go back and understand it.
A meter is defined as the distance light travels in a vacuum in 1/299,792,458th of a second.
Ben Hocking
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