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perpetual motion

noun, Mechanics.
1.
the motion of a theoretical mechanism that, without any losses due to friction or other forms of dissipation of energy, would continue to operate indefinitely at the same rate without any external energy being applied to it.
Origin of perpetual motion
1585-1595
1585-95
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2016.
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British Dictionary definitions for perpetual-motion

perpetual motion

noun
1.
Also called perpetual motion of the first kind. motion of a hypothetical mechanism that continues indefinitely without any external source of energy. It is impossible in practice because of friction
2.
Also called perpetual motion of the second kind. motion of a hypothetical mechanism that derives its energy from a source at a lower temperature. It is impossible in practice because of the second law of thermodynamics
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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