The Kilogram gets redefined

On Friday, November 15, scientists met in Versailles, France at the General Conference on Weights and Measures. There they voted to change the definition of a Kilogram. This official change will take place on May 20, 2019, aka World Metrology Day.  

Since 1889, the kilogram was defined by “the weight of a platinum-based ingot called ‘Le Grand K’ which is locked away in a safe in Paris.” Several replicas have been made and distributed around the world, used to calibrate scales so that the whole world is using the same system of measurement. Now, the kilogram will be defined regarding electric current, using an electromagnet. “It’s making history,” says student Sumaya Saddiq.

A big reason for this change is because the “Big K” doesn’t weigh the same amount as it did when it was first created. Over time, this ingot and its copies lost 50 micrograms, which is about the weight of an eyelash. Though it doesn’t seem like much, it makes a big difference when it comes to measuring.

So how does this new system work? The pull of an electromagnet is directly related to the amount of electrical current going through it. Using the electromagnet, scientists can measure the weight of a kilogram “in terms of the amount of electricity needed to counteract the weight” according to BBC.com.

The only issue with the use of electromagnet is that the unit it’s measured in is tiny, called Planck’s constant, or h. The Kibble Balance, built by Dr. Bryan Kibble, has an electromagnet that is placed on one side of a scale and a weight (i.e., a kilogram) on the other. Then, an electrical current goes through the magnet until both sides are equal.

So, the kilogram will be measured based on how much electricity in terms of h is needed to have the scales be balanced. This new system brings many advantages, including the fact that a kilogram can now be measured anywhere at any time instead of just in a location that has “Big K’ or one of its copies.  

Sophomore Ella Lau thinks this change is a great idea, saying “This new system will make everything easier and way more accurate. I’m glad they’re making the change!”


Sophia DiPrima