# Power

PowerÂ measures howquickly work gets done. For example, a force of 100J of work in 20 seconds is being done at a rate of 100J/20s = 5J/s. This is the power (P), and from sample calculation above the units are obviously J/s. This is defined as the watt, W, which should not be confused with the *W* which defines work.

Power = work/time = *W*/*t*

The faster work gets done, the greater the power. If there is constant *v* and force is parallel to path, then P = Fv

Energy is the ability to do work. Moving objects inherently have energy because they can crash into something and exert a force over a distance. Kinetic energy is this energy of motion.

Fd=.5mv^{2}

W=.5mv^{2}

KE = .5mv^{2}

This assumes the initial speed of the object is 0. If it were not, then W = KE_{final} - KE_{initial}.W^{total} = ΔKE.

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Potential energy is energy of an object due to position. There is gravitational, electrical, and elastic potential energy. Potential energy is placed on position in a gravitational field. ΔPE_{grav}=-W_{by Fgrav}=mgh. If the brick had fallen, it would have been -mgh.

PE = -mgh

Gravity is a conservative force.