- At the General Conference on Weights and Measures on November 16 in Versailles, nations unanimously approved new scientific definitions for the kilogram and other units. Researchers voted to get rid of it in favour of defining a kilogram in terms of an electric current.
- Currently, it is defined by the mass of a cylinder of a platinum-based ingot called “Le Grand K” which is locked away in a safe in Paris. Le Grand K has been at the forefront of the international system of measuring weights since 1889. Several close replicas were made and distributed around the globe. But its copies were seen to change – ever so slightly – as they deteriorated.
- That is why the new kilogram will be defined in terms of a tiny but unchanging value called the ‘Planck constant’. The ‘Planck constant’, that derives from quantum physics, can be used along with a Kibble balance, an exquisitely accurate weighing machine, to calculate the mass of an object using a precisely measured electromagnetic force.
- Electromagnets generate a force. Scrap-yards use them on cranes to lift and move large metal objects, such as old cars. The pull of the electromagnet, the force it exerts, is directly related to the amount of electrical current going through its coils. There is, therefore, a direct relationship between electricity and weight.
- So, in principle, scientists can define a kilogram, or any other weight, in terms of the amount of electricity needed to counteract the weight (gravitational force acting on a mass).
