A flywheel includes a shaft a rotor attached to the shaft. The rotor rotates using the shaft as a central axis. The rotor includes at least one magnet along an outer circumferential surface thereof, at least one coil spaced apart from the rotor in a radial direction. The coil may form a magnetic field that exerts a magnetic force on the magnets when current is supplied to the coil by an electric circuit, thus mitigating fluctuations in rotation of the rotor.