# Kinetic energy

## Energy of a moving physical body / From Wikipedia, the free encyclopedia

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In physics, the **kinetic energy** of an object is the form of energy that it possesses due to its motion.^{[1]}

**Quick Facts**Common symbols, SI unit ...

Kinetic energy | |
---|---|

Common symbols | KE, E_{k}, K or T |

SI unit | joule (J) |

Derivations from other quantities | E_{k} = 1/2mv^{2} E_{k} = E_{t} + E_{r} |

In classical mechanics, the kinetic energy of a non-rotating object of mass *m* traveling at a speed *v* is ${\textstyle {\frac {1}{2}}mv^{2}}$.^{[2]}

It can be shown that the kinetic energy of an object is equal to the work needed to accelerate an object of mass *m* from rest to its stated velocity. Having gained this energy during its acceleration, the object maintains this kinetic energy unless its speed changes. The same amount of work is done by the object when decelerating from its current speed to a state of rest.^{[2]}

The SI unit of kinetic energy is the joule, while the English unit of kinetic energy is the foot-pound.

In relativistic mechanics, ${\textstyle {\frac {1}{2}}mv^{2}}$ is a good approximation of kinetic energy only when *v* is much less than the speed of light.