Theoretically, is it possible to store huge amount of energy using a flywheel that spins at speeds that approach light speed? Can the amount of energy be higher than the mass equivalence of the wheel?
Theoretically, it would be possible to accelerate any mass, even spin a flywheel, to near light speed. As mass increases with speed, relativistic mass could be many times the rest mass. In practice, however, with any material available today, a flywheel would tear itself to pieces long before reaching relativistic speeds.