Perpetual motion machine

A hypothetical machine that runs indefinitely or produces useful work without an energy source. Its operation would violate established laws of thermodynamics.

First law of thermodynamics: The principle that energy is conserved: it cannot be created or destroyed, only transferred or transformed. A machine producing work without an energy input would violate energy conservation.
Bhaskara II: A twelfth-century Indian mathematician whose writings describe a wheel intended to turn perpetually. His self-turning wheel is among the best-known early perpetual-motion proposals.
Maxwell's demon: A thought experiment in which an intelligent being sorts gas molecules in ways that appear to reduce entropy. It tests the second law through information and measurement rather than a mechanical perpetual-motion design.
Perpetual motion patent: A patent application or grant concerning a machine claimed to operate perpetually or produce work without adequate input. Patent offices have used thermodynamic impossibility as grounds for requiring working models or rejecting such claims.
Second law of thermodynamics: The principle that the total entropy of an isolated system cannot decrease in spontaneous processes. A cyclic machine converting heat from one reservoir entirely into work would violate this law.
Villard de Honnecourt: A thirteenth-century French architect and engineer known for a surviving illustrated portfolio of designs. His portfolio includes a proposed overbalanced wheel that would supposedly turn continuously.
Brownian ratchet: A proposed device that seems to extract directed motion from random thermal fluctuations. Its apparent one-way motion illustrates why thermal noise cannot power a perpetual-work machine.
Patent model: A physical model submitted to demonstrate how an invention is intended to work. Historical demands for models exposed claims that lacked a functioning mechanism.
Perpetual motion machine of the first kind: A proposed machine that produces net energy without receiving energy from outside. This subtype directly contradicts the first law of thermodynamics.
Cornelis Drebbel: A Dutch inventor and engineer active in the late sixteenth and early seventeenth centuries. A self-moving perpetual clock was attributed to him, though its mechanism and status remain uncertain.

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