Perpetual motion is the motion of that continues forever in an unperturbed system. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an external source. This kind of machine is impossible, since its existence would violate the and/or laws of thermodynamics. These apply regardless of the size of the system.
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Flywheel energy storage (FES) works by spinning a rotor () and maintaining the energy in the system as . When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of ; adding energy to the system correspondingly results in an increase in the speed of the flywheel.
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