# Mechanical Energy

Mechanical energy includes, on the one hand, potential energy or
energy of position; for example, the potential energy *E*_{pot}
of a mass m 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 as
well.

There is also kinetic energy or 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
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 reconstruction 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.

Pictured at the right is a reconstruction of a thousand year old design for the construction of a continuously rotating wheel. It is located in the museum of the Institute for the History of Arabic-Islamic Science at the University of Frankfurt a.M.