The definition of a kilogram is officially going to change
The definition of a kilogram is officially going to change
Scientists set to change definition of the kilogram
18 November, 2018, 05:43
Weighing stuff just got more thrilling, as the world metrological community has now redefined the kilogram-and other quantities-to be based on physical constants. "We can now measure everything more accurately using knowledge of how the universe operates at the atomic level than we can using objects we can can see and feel". He asked what would happen if a fingerprint got on the kilogram prototype and increased its mass. The change puts electrical measurements back into the SI where all other measures are made.
From May 20, 2019, the definition of kilogram will be based on the Planck constant, a concept of physics.
All modern mass measurements are derived from the kilogram, whether micrograms of pharmaceutical medicine or gold dust, kilos of fruit or fish, or tonnes of steel.
The metal kilo is being replaced by a definition based on Planck's constant, which is part of one of the most celebrated equations in physics but also devilishly hard to explain.
In a similar way, the SI unit for the ampere will now be based on the constant for the charge of the electron.
Perdi Williams from the National Physical Laboratory said: "The new system is going to work a lot better". "As an historic artefact that has been under study for 140 years, it will continue to be important for researchers for years to come", it says. Using combinations of these constants and the equations of quantum mechanics, scientists created revised SI units for measuring mass, electric current, temperature and the mole that are at least one million times more stable than artifacts like Le Grand K. Today knowing that a kilogram is a kilogram is done with a set of global prototype kilogram weights made from very hard metals like platinum, but even that isn't entirely accurate.
"We know from comparing the kilogram in Paris with all the copies of the kilogram that are all around the world that there are discrepancies between them and Le Grand K itself", Dr Stuart Davidson, head of mass spectrometry at the National Physical Laboratory in the United Kingdom told the BBC. SI is the International System of Units, through which measurements are communicated. The new definition of a kelvin promises advantages for scientists needing to make very precise measurements.
Instead of checking it against an actual weight, scientists can now find an exact kilogram by measuring the amount of electricity needed to lift it, using a special set of scales known as The Kibble balance.
For 130 years, a kilogram has been defined by a lump of metal sitting in a vault in Paris.
It was originally called a "watt" balance, the SI unit of power. According to its original design, the kilogram was "equal to the mass of a liter of water".
The new method, decided at the General Conference on Weights and Measures in Paris on Friday, will be a formula called the "Planck constant".
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