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Perpetual motion describes "Motion that continues indefinitely without any external source of energy; impossible in practice because of friction." It can also be described as "the motion of a hypothetical machine which, once activated, would run forever unless subject to an external force or to wear". There is a scientific consensus that perpetual motion in an isolated system would violate the first and/or the second law of thermodynamics.

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There is no such thing as real perpetual machine, as it defies the law of thermodynamics. Friction is definitely present as the ball goes around the track,and the air resistance force too. The magnets …
answered Sep 22 '12 by James Kujareevanich