A flywheel is a rotating mechanical device that
is used to store rotational energy. Flywheels have an inertia
called the moment of inertia and thus resist changes in
rotational speed. The amount of energy stored in a flywheel is
proportional to the square of its rotational speed. Energy is
transferred to a flywheel by the application of a torque to it,
thereby increasing its rotational speed, and hence its stored
energy. Conversely, a flywheel releases stored energy by applying
torque to a mechanical load, thereby decreasing the flywheel's
rotational speed.
