David Kirkpatrick

June 2, 2010

Redefining the kilogram

Filed under: Science — Tags: , , , — David Kirkpatrick @ 2:50 pm

Fun with science

From the link, the problem:

Now physicists want to do the same for the kilogram, which is currently defined as the mass of a cylinder of platinum and iridium called the International Prototype Kilogram.

That’s a problem because each time it is picked up, a few atoms rub off the cylinder making it imperceptibly lighter. For this reason almost nobody is allowed to measure the mass of the International Prototype Kilogram, which is stored in a vault in Sevres in France. So nobody really knows how much mass the kilogram is losing or indeed, whether it is gaining the weight of a thin layer of dust and impurities which must surely be gathering on its hundred year-old surfaces.

And one proposed solution:

So Fox and co have another suggestion. Why not make the kilogram equal to the mass of a certain number of carbon-12 atoms, specifically 2250× 28148963^3 of them?

Then a kilogram would be a cube of carbon 8.11cm on each side (8.11cm is roughly the length of 368,855,762 carbon atoms laid side by side).

With that definition, almost anybody could make a kilogram in their own kitchen given some carbon and a knife.

“The day we made a kilogram” might even be the kind of fun that could engage and inspire a new generation of scientists, which ought to be a good enough reason on its own on which to decide.

Note: it’s totally worth hitting the link just to read the comments.

1 Comment »

  1. What a great idea! (The carbon atoms one). I’ve always worried about the current definition myself for the reasons stated. With this definition we can feel safe the definition stays fixed.

    Thanks for alerting us about this.

    Comment by Joseph Smidt — June 2, 2010 @ 8:50 pm

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