Flywheel

A flywheel is a mechanical device that uses the <a href="/facts/Conservation_of_angular_momentum/7TuSVFxq">conservation of angular momentum</a> to store <a href="/facts/Rotational_energy/sFhMenoK">rotational energy</a>, a form of kinetic energy proportional to the product of its <a href="/facts/Moment_of_inertia/TpLLAVl7">moment of inertia</a> and the square of its <a href="/facts/Rotational_speed/DAVXQgXj">rotational speed</a>. In particular, assuming the flywheel's moment of inertia is constant (i.e., a flywheel with fixed mass and <a href="/facts/Second_moment_of_area/TludHUKK">second moment of area</a> revolving about some fixed axis) then the stored (rotational) energy is directly associated with the square of its rotational speed.
Since a flywheel serves to store mechanical energy for later use, it is natural to consider it as a <a href="/facts/Kinetic_energy/aJRxUd4p">kinetic energy</a> analogue of an <a href="/facts/Capacitor/hyowqv7n">electrical capacitor</a>. Once suitably abstracted, this shared principle of energy storage is described in the generalized concept of an <a href="/facts/Accumulator_(energy)/qnvvAVvb">accumulator</a>. As with other types of accumulators, a flywheel inherently smooths sufficiently small deviations in the power output of a system, thereby effectively playing the role of a <a href="/facts/Low-pass_filter/QFsUjw7h">low-pass filter</a> with respect to the mechanical velocity (angular, or otherwise) of the system. More precisely, a flywheel's stored energy will donate a surge in power output upon a drop in power input and will conversely absorb any excess power input (system-generated power) in the form of rotational energy.
Common uses of a flywheel include smoothing a power output in <a href="/facts/Reciprocating_engine/ItLAxmW3">reciprocating engines</a>, <a href="/facts/Flywheel_energy_storage/YwXWjuRo">flywheel energy storage</a>, delivering energy at higher rates than the source, and controlling the orientation of a mechanical system using <a href="/facts/Gyroscope/UjXGsfMq">gyroscope</a> and <a href="/facts/Reaction_wheel/m3M5RKGF">reaction wheel</a>. Flywheels are typically made of steel and rotate on conventional bearings; these are generally limited to a maximum revolution rate of a few thousand <a href="/facts/RPM/fdNmLToF">RPM</a>. High energy density flywheels can be made of carbon fiber composites and employ <a href="/facts/Magnetic_bearing/AF9sRk6F">magnetic bearings</a>, enabling them to revolve at speeds up to 60,000 RPM (1 <a href="/facts/KHz/6Wshj5qm">kHz</a>).

Flywheel open-in-new

Flywheel