# kinetic energy

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## kinetic energy:

see energy**energy,**

in physics, the ability or capacity to do work or to produce change. Forms of energy include heat, light, sound, electricity, and chemical energy. Energy and work are measured in the same units—foot-pounds, joules, ergs, or some other, depending on the system of

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## kinetic energy

(ki-**net**-ik) Energy possessed by a body by virtue of its motion, equal to the work that the body could do in coming to rest. In classical mechanics a body with mass

*m*and velocity

*v*has kinetic energy ½

*mv*

^{2}. A body with moment of inertia

*I*rotating with angular velocity ω has kinetic energy ½

*I*ω

^{2}.

## Kinetic Energy

the energy of a mechanical system, which depends on the velocity of motion of its points. The kinetic energy *T* of a mass point is equal to one-half the product of the mass *m* of the point and the square of its velocity *ν: T = ½ mν ^{2}.* The kinetic energy of the system is equal to the algebraic sum of the kinetic energies of all of its points:

*T*=

*Σ½mν*The expression for the kinetic energy of the system may also be written in the form

_{k}^{2}.*T = ½Mν*+

_{c}^{2}*T*, where

_{c}*M*is the total mass of the system,

*νc*is the velocity of the center of mass, and

*T*is the kinetic energy of the motion of the system about the center of mass. The kinetic energy of a rigid body in translational motion is calculated in the same way as the kinetic energy of a point with mass equal to the total mass of the body.

_{c}When the system is displaced from configuration (1) to configuration (2) the change in the system’s kinetic energy arises from the action of external and internal forces applied to it and is equal to the sum of the work *A _{k}^{e}* and

*A*performed by the forces over the given displacement:

_{k}^{i}*T*—

_{2}*T*=

_{1}*Σ*+

_{k}A_{k}^{e}*Σ*. This equation expresses the theorem of the change in kinetic energy, which is used in solving many problems in dynamics.

_{k}A_{k}^{i}At velocities approaching the speed of light, the kinetic energy of a mass point is

where *m _{o}* is the rest mass of the point,

*c*is the speed of light in vacuum (

*m*is the energy of the point at rest). At low velocities (ν «

_{o}c^{2}*c*) the above equation is transformed into the usual

*½mν*formula.

^{2}S. M. TARG

## kinetic energy

[kə′ned·ik ′en·ər·jē]## kinetic energy

**translational kinetic energy**depends on motion through space, and for a rigid body of constant mass is equal to the product of half the mass times the square of the speed. The

**rotational kinetic energy**depends on rotation about an axis, and for a body of constant moment of inertia is equal to the product of half the moment of inertia times the square of the angular velocity. In relativistic physics kinetic energy is equal to the product of the increase of mass caused by motion times the square of the speed of light. The SI unit is the joule but the electronvolt is often used in atomic physics.