Thinking about weight and other matters.

image taken from The international Bureau of Weight and Measures

The kilogram is the last remaining base unit of the SI that is defined by a physical object and although there are many copies of it, the one that matters is housed at the International Bureau of Weights and Measures [or to be correct - Bureau International des Poids et Measures] in Serves, south west of Paris.

The international prototype and it's six official copies are kept in a vault there under lock and key.Made in 1880s the original and four of it's copies stem from that date [for some reason the Bureau does not know or reveal their precise birth dates].From these copies a further 80 copies have been made and been distributed internationally for all to measure against.

To dispel ambiguities concerning the kilogram a resolution was passed at the 3rd meeting of the CGPM [General Congress of Weight and Measure] in 1901 concerning the meaning of weight which was used sometimes for mass or as a mechanical force.

So to be clear the CGPM declared,

"1.The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram;

2.The word "weight" denotes a quantity of the same nature as a "force": the weight of a body is the product of its mass and the acceleration due to gravity; in particular, the standard weight of a body is the product of its mass and the standard acceleration due to gravity;

3.The value adopted in the International Service of Weights and Measures for the standard acceleration due to gravity is 980.665 cm/s², value already stated in the laws of some countries."

Needless to say the maintenance of the kilogram and therefore the cleaning and accumulation of surface contaminants are of concern.Curiously all seven have been treated the same and kept in similar conditions yet the masses amongst them are drifting apart.The result is that the kilogram has on an average lost weight by roughly 50 micrograms or the weight of a fingerprint.The trouble is no one knows exactly why.

This 'news' was revealed to me by The Guardian.

Which takes me onto Buckminster Fuller and Cedric Price and the interest in the lightweight but I think I'll save that for another post.