perpetual motion

American  

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.

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perpetual motion British  

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

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Etymology

Origin of perpetual motion

First recorded in 1585–95

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Example Sentences

See Examples For:

perpetual motion

Here, perpetual motion tips over into physical comedy.

From Los Angeles Times ● Jun. 11, 2026

Hughes is the NHL’s perpetual motion machine, the defenseman who never stops skating.

From The Wall Street Journal ● May 3, 2026

The objective of the value investor like Buffett is to make money over the long term, but the manner in which this is accomplished is also in perpetual motion.

From Barron's ● Dec. 12, 2025

“If that occurred with cloud seeding, they’d have water all the time. You can’t create rain out of thin air per se and get 6 inches of water. That’s akin to perpetual motion technology.”

From Seattle Times ● Apr. 17, 2024

And Josie might as well have been a perpetual motion machine, her head spinning around to gaze at everything in wonder, her toes tapping, her fingers fidgety.

From "The School for Whatnots" by Margaret Peterson Haddix

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