Magazine article ASEE Prism

Weight of the World

Magazine article ASEE Prism

Weight of the World

Article excerpt

"THE MASS OF A kilogram is a kilogram," explains William Phillips, a physics professor at the University of Maryland.That's easy enough to understand. But here's the problem; The mother of all kilograms - the international prototype that's been housed in a bunker in suburban Paris since the 1 9th century and sets the standard for all others - has shed a bit of weight. Not a lot: about 50 micrograms, roughly the mass of a speck of sand. Why? No one's entirely sure, but the main suspect is cleaning. Of all the international base units of measurement, including the meter, the ond, and the kelvin, only the kilogram is still linked to a man-made object. The meter, for instance, is now officially measured by how far light travels in a certain length of time, which isa mere 1/299,792,458 of a second. …

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