perpetual-motion machine

A machine that could run forever. A perpetual-motion machine would have to produce at least as much energy as was needed for its operation. According to the second law of thermodynamics, such a machine is impossible, and to date none has ever been successfully demonstrated.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.