The definition of Kilogram from now has been changed forever.
Kibble Balance. Image credit: NIST

The definition of Kilogram from now has been changed forever.

What if I ask you, what do you understand by the Kilogram? You would definitely tell me that it is the unit of mass. Yes, of course, you are right but do you know, how it’s defined? After more than 130 years the definition of Kilogram now has been changed forever. What has it’s mean now, you will be able to get it in this article. So, without any further ado, let’s get started.

The decision of changing the definition of Kilogram and the other three units i.e Ampere, Kelvin and Mole, made at the General Conference on Weights and Measures in Versailles, France on World Metrology Day i.e. 20 May 2019, organized by the International Bureau of Weights and Measures (BIPM).

From now all the SI units will now be defined in terms of constants and end to the use of physical objects to define measurement units. This will ensure the future stability of the International System of Units (SI) units and open the opportunity for the use of new technologies, including quantum technologies, to implement the definitions.

Now comes to the headline i.e the definition of the Kilogram. For more than 130 years, it is defined as, a metal cylinder (the International Prototype of the Kilogram (IPK)) of a platinum alloy stored at the BIPM vault in France, but from now it will be retired.

Le Grand K. Image credit:

And from now on it will be defined by the Plank constant. The Planck constant relates a photon’s energy to its frequency. This incredibly small number has to be measured by a very sensitive Kibble balance that uses a powerful magnetic field to do its work.

Watt balance. Image credit: J. L. Lee / NIST

And according to the new definition, the magnitude of a Kilogram would be “set by fixing the numerical value of the Planck constant to be equal to exactly 6.626069… × 10E-34 when it is expressed in the SI unit s‾ ¹m² kg, which is equal to J-s.”

Note: Representatives from 60 countries voted to redefine the International System of Units (SI).

Now an obvious question might arise in front of you that “Why all three?” This is because of the unit of Planck constant. Its unit is kg-m²/s. So at first, we need to define the Metre, Second and the Kilogram.

For example, a Metre is determined by the distance light travels in a vacuum in 1/299792458 of a second. A Second is determined by the time it takes for a caesium atom to oscillate 9,192,631,770 times.

  • The Ampere will be defined by the elementary electrical charge (e).
  • The Kelvin will be defined by the Boltzmann constant (k).
  • The Mole will be defined by the Avogadro constant (N).

Researchers will now be able to weigh things accurately without going to France to compare them with the cylinder, known as Le Grand K because if it lost or gained some mass, the definition of the Kilogram would alter.

Martin Milton, the Director of International Bureau of Weights and Measures (BIPM) said “The SI redefinition is a landmark moment in scientific progress. Using the fundamental constants we observe in nature as a foundation for important concepts, such as mass and time, means that we have a stable foundation from which to advance our scientific understanding, develop new technologies and address some of society’s greatest challenges.”

Let me remind you that this will not affect the normal life of us in any way. The kilogram will still be a kilogram like we measure earlier, but it means a lot for scientists and researchers.

Just as the redefinition of the second in 1967 provided the basis for technology that has transformed how we communicate across the globe, through GPS and the internet, the new changes will have a wide-reaching impact in science, technology, trade, health, and the environment, among many other sectors.

So that’s it for today guys. Did you enjoy reading this article? If so, then please share it. If you have any suggestions and queries related to the post, let me know in the comment section below. Please do like and share this post to your near and dear ones to explore the knowledge you must know.

Thank you.

Anil Kashyap

I want to explore new things every single moment of life. Life motto: Learn and teach as much as you can until your last breath.

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