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REAL LIFE NEWS: HOW MUCH DOES A KILOGRAM WEIGH?

by Hazed

That may seem like a meaningless question... a kilogram weighs a kilogram, of course. But what does that mean? What determines the weight that we call a Kg?

The answer is that the official SI definition of a kilogram is a mass equal to that of the international prototype kilogram, a cylinder of platinum and iridium kept in a vault near Paris, France. It lives in an environmentally monitored room, and is inside several nested glass cases. There is an elaborate cleaning procedure that is carried out to remove atmospheric oxidants from the surface, to make sure its mass doesn't change. But in reality, it does not stay absolutely constant - when it's compared from time to time to other exact copies held by other nations, it can be seen that slight changes, on the order of micrograms (a billionth of a kilo) do happen.

Who cares about such teensy changes? Well, scientists at the Consultative Committee for Units do. They want to change the standard so that instead off being determined by a physical object, it is set by the use of something less concrete. They want to use Planck's constant, which is expressed in kilograms square-meters per second, to determine the exact mass of the kilogram.

All the other base SI units, such as the meter, have already stopped using physical objects so making this change to the official kilogram measure would bring it in line with the rest.

The body in charge of SI units has approved substituting the platinum-iridium cylinder with the Planck measurement, and how international diplomats at the General Conference on Weights and Measures will make the final decision next year.

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