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When does an object has energy
if it can produce a change in itself or in its surroundings.

Work
 is the product of the net force exerted on an object and the distance the object moves in the direction of the force.
 W = Fd N·m = Joule (J)
 If force is at an angle: W = Fd cos θ (cos 90o = 0)
 Work is the transfer of energy by mechanical means. Energy is the ability to change an object.

Kinetic energy (KE):
energy an object has because of its motion.

Potential energy (PE):
energy an object has because of position, shape or form.

The net work done on an object is equal to its change in KE.
F = ma W = Fx W = max

Gravitational PE
 depends on the weight of the body and its separation from Earth.
 PE = mgh

How does PE depend on height?
 (Recall this equation: vf2 = vi2 + 2gx and multiply each term by ½ m)
 E = ½ mvf2 = ½ mvi2 + mgh
 If h = 0, then E = ½ mv2
 If v = 0, then E = mgh
 Total E = KE + PE
 Note: need a reference level to calculate PE

Elastic potential energy
is energy available for use when a deformed elastic object returns to its original configuration.

The sum of KE + PE = mechanical energy.

the Law of Conservation of Energy
 According to the Law of Conservation of Energy, the total energy of a closed, isolated system is constant.
 (If something is conserved, we mean it remains constant.)
 Energy can change form but the total energy does not change.
 Note: mechanical energy is not conserved in the presence of friction.

Power
 is the rate of doing work or the rate at which energy is transferred.
 P = W/t J/s = Watt (W) P = Fd/t = Fv

