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Kinetic and potential energy

Kinetic energy is the energy of motion and grows with the square of the speed. Potential energy is stored energy due to position, for example height in a gravitational field. The height is measured from a reference level you choose yourself, and only height differences matter.

E_k = \tfrac12 mv^2

kinetic energy

E_p = mgh

potential energy in a gravitational field

Symbols

$E_k$	kinetic energy	J
$E_p$	potential energy	J
$v$	speed	m/s
$h$	height above the reference level	m

Example

A bicycle with rider, $m = 80$ kg, moves at $v = 10$ m/s. Kinetic energy: $E_k = \tfrac12\cdot 80\cdot 10^2 = 4000$ J $= 4.0$ kJ.

Doubling the speed quadruples the kinetic energy – it depends on

v^2

, not

v

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Part of Foundations of Physics: Work, energy and power.