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Prototype kilogram replica

Definition of kilogram changed for the first time in 130 years

The metric system originated in the times of the French Revolution. During those periods, many different units of measurement were being used. The number went as high as 250,000 resulting in confusion and difficulty of trade in the country. Hence the new system was introduced that was meant to be uniform throughout and not vary according to the whims of the local rulers.

In the current International system of units, a few units are defined in such a way that they are the same anywhere in the universe, but a few like Kilogram are not defined like this. The kilogram was defined by a Platinum-Iridium cylinder, which is clearly not a standard definition.

The Le Grand K has served as the international prototype for the kilogram for 130 years. This golf sized material is composed of 90% of platinum and 10% iridium.


However, this arrangement posed several problems. If Le Grand K got contaminated and became heavier, then it meant that the kilogram grew heavier. On the other hand, if it lost weight, it resulted in the kilogram being lighter. It has been estimated that over time, the kilogram has lost nearly 50 micrograms of mass.

But now it will no longer be a standard for the kilogram. It has been replaced with the Planck’s constant. Being a natural property, its value cannot change with time as it is ingrained into the existence of the universe. Stephan Schlamminger, a scientist at the National Institute of Standards and Technology commented that a fundamental constant can never change its value, unlike any physical quantity. As a result of this, now the value of the kilogram will be same on Earth as in any other part of the universe.

Scientists who have been associated with the science of measurement for a very long period view this new definition of the kilogram along with similar changes in mole, ampere and Kelvin as a great advancement of humanity.

However, most of our daily calculations will be unaffected by this change. This decision to modify the four basic units of the International System of Units was made at the 26th General Conference on Weights and Measures in November of 2018. The change was accepted unanimously by the delegates of the 60 member nations who had gathered.


However, the copies of Le Grand K will not be useless immediately as they would be used as a standard of kilogram by NIST.

Do you think that these standards are really the final standards or something more precise and universal can be found? Tell us with a short and quick comment.

About the author: Kalpit Veerwal
Kalpit Veerwal is a second year Computer Science undergraduate at IIT Bombay. He is well known for being the only person to score 360/360 in JEE (Main). He is registered in the Limca Book of Records for the same. A blogger in his free time, he has also secured top ranks in various exams held in India and the world.

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