Mechanical energy includes: *potential energy*, also known as *energy of position*.
The potential energy *E*_{pot} of a mass *m*, for example, is equal to
*E*_{pot} = *m g h*, where *g* is the acceleration due to gravity
and *h* is the height. Potential energy can be found in elastic deformation, in which the original
shape of a material is recovered after an external force is removed.

There is also *kinetic energy*, also known as *energy of motion*,
*E*_{kin} = ½ *m v*^{2},
which arises from the motion of a mass *m* with a velocity *v*.
Similar to kinetic energy of translation (the energy of moving from place to place)
the rotational energy of a body with angular velocity *ω* and a moment of inertia
*Ⅰ* with respect to the rotational axis is described by
*E*_{rot} = ½ *Ⅰ* *ω*^{2}.

When mechanical energy is not converted to another energy form (other than potential energy), the principle of conservation of mechanical energy applies:

This describes, for example, the undamped vibration of a pendulum. An experimental proof of the conservation of mechanical energy is the fact that one cannot build a perpetual motion device.

The picture at the left is a replica (exhibited in the museum NAWCC) of a clock presented in 1815 by David Geiser as a perpetual motion device. After his early death in 1817, it became known that the device did not, in fact, run continuously.

The picture at the right depicts a thousand year old design for the construction of a continuously rotating wheel. It runs continuously indeed, but only on the Internet page www.hp-gramatke.de.