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Experts Suggest Replacing Definition of Kilogram

Posted by Zonk on from the still-won't-be-used-in-the-states dept.

fenimor writes "The kilogram is the only one of the seven basic units of the international measurement system defined by a physical artifact rather than a natural phenomenon. International team of scientists suggest replacing the kilogram artifact -- a cylinder of platinum-iridium alloy about the size of a plum --with a definition based on one of two unchanging natural phenomena, either a quantity of light or the mass of a fixed number of atoms. They propose to adopt either one of two definitions for the kilogram by selecting a specific value for either the Planck constant or the Avogadro number."

2 of 844 comments (clear)

  1. Re:Anyone Else? by TheEternalVortex · · Score: 5, Informative

    The SI unit of mass is the kilogram, not the gram.

  2. Re:Picture of the Kilogram Prototype by ink_13 · · Score: 5, Informative
    To keep its mass from changing. You may notice the calipers for handling it in the picture, too. Stray moisture, direct sublimation into the atmosphere, anything that could possibly affect it has to be kept away,

    This is the definition of the kilogram. A kilogram is not 1L of H2O at STP (as mentioned elsewhere, pressure depends on mass), it's this little lump of metal. Changes in the mass of it are extraordinarily bad. They make copies of it for reference purposes, and then check the copies agains the original every 10 years. If there's a disagreement, the copy gets adjusted, not the original. The reference lump has actually lost about 50 micrograms in the last 100 years (and no one knows why). That's a lot (well, speaking at the level that micrograms get used at... 1 microgram = 0.000000001 kg), and the really highlights the need for an immutable reference point.

    Readers may find the pertinent Wikipedia article interesting.