Unit of the month: KILOGRAM
20 May 2019
Mass is a quantity that has been inseparably bound to humanity for thousands of years. The need to trade goods is a fundamental part of any civilization, and the methods to do so are constantly developing. Our first records of using measurement standards in trade come from a few thousand years BC, in ancient Egypt. The ancient Egyptians employed stones to check the weight of goods, later stones were replaced by standards casted from bronze. Amazingly, until yesterday we did something very similar. The International Mass Standard was also a material measure – cylinder made of platinum-iridium alloy.
Today, new definitions of the SI base measurement units come into force, one of them being the kilogram, our unit for May – the last unit we’ll be looking at.
Definition of the kilogram up to 20th of May 2019 was as follows:
The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.
From today, the new definition comes into force:
The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10−34 when expressed in the unit J s, which is equal to kg m2 s−1,where the metre and the second are defined in terms of c and ∆νCs.