Kinetic energy

Lore & Background

The principle that kinetic energy is proportional to mass times velocity squared was developed by Gottfried Leibniz and Johann Bernoulli, who described it as 'vis viva' (living force). Émilie du Châtelet recognized the implications and published an explanation. The terms 'kinetic energy' and 'work' in their present scientific meanings date to the mid-19th century.

Reader's Guide

Kinetic energy is fundamental to physics, representing the energy an object has due to motion. In classical mechanics, it is calculated as ½mv², a formula accurate for speeds much less than the speed of light. The concept is conserved in elastic collisions and can be transformed into other energy forms, such as potential energy, heat, or electrical energy. Examples include a cyclist converting chemical energy into kinetic energy, a spacecraft gaining kinetic energy to reach orbit, and billiard balls transferring kinetic energy in collisions. Kinetic energy is not invariant; it depends on the observer's frame of reference. Its historical development from vis viva to modern terminology illustrates the evolution of physics. The SI unit is the joule; the English unit is the foot-pound. Relativistic mechanics requires a different formula when speeds approach the speed of light.

Did You Know?

• The adjective 'kinetic' comes from the Greek word κίνησις (kinesis), meaning 'motion'.
• The same amount of work done to accelerate an object from rest to a given speed is done by the object when decelerating to rest.