Forget the kilogram as you were taught at school; it is obsolete today! Indeed, it is at the beginning of the week that the new world definition of the kilogram has come into force.
Acted last November in Versailles by the General Conference of Weights and Measures, which meets every four to six years, this decision establishes a new system of international measurement for the good old kilogram. The ampere, the kelvin and the mole are also concerned by this historic redefinition voted by the representatives of 60 countries.
The new system therefore has since May 20, the kilogram is no longer defined from the “big K”, but the constant Planck.
Technically, the kilogram was until then defined as equal to the mass of the “big K”, a cylinder made of platinum and iridium and carefully preserved since 1889 at the International Bureau of Weights and Measures in Sèvres (Hauts-de -Seine).
Recently, however, scientists have noticed that the mass of the international prototype has varied slightly compared to those of the six control copies made at the same time.
This variation, although it may seem small for a lambda person, is nevertheless important today that science and industry have passed the “nano measure”, or even smaller.
That is why the new definition of the kilogram has been drawn from quantum physics, to be defined from the Planck constant (h).
In addition to the kilogram, the kelvin, measured from water, will be redefined from the Boltzmann constant (k), related to the measurement of thermal agitation of the fundamental constituents of a body.
The ampere will be connected to the elementary charge (e), the electric charge of a proton.
The mole, the unit of quantity of matter, used essentially in chemistry, will be defined directly by fixing the Avogadro constant (NA).