perpetual-motion machine

perpetual-motion machine device that would be able to operate continuously and supply useful work, in violation of the laws of thermodynamics . A machine that would produce more energy in the form of work than is supplied to it in the form of heat would violate the first law of thermodynamics, which is a special case of the law of conservation of energy (see conservation laws , in physics), and is known as a perpetual-motion machine of the first kind. A machine that would completely convert heat from a warm body into work, without letting any heat flow into a cooler body, would violate the second law of thermodynamics, which is concerned with entropy changes, and is known as a perpetual-motion machine of the second kind. There were a number of early attempts to design and construct various types of perpetual-motion machines; however, since the 19th cent., when the laws of thermodynamics became understood, most such attempts have been abandoned.

perpetual motion Hypothetical machine that continues to work without any energy being supplied. Such a machine would require either the complete elimination of friction, or would have to violate the laws of thermodynamics.

per·pet·u·al mo·tion • n. a state in which movement or action is or appears to be continuous and unceasing. ∎  the motion of a hypothetical machine that, once activated, would run forever unless subject to an external force or to wear.