work continuously done without an external supply of energy
Perpetual motion refers to a machine or system that could theoretically work continuously without needing an external supply of energy. It matters because such a machine is impossible according to the laws of physics, which is why understanding why perpetual motion cannot exist helps us grasp fundamental principles about how energy works in our universe.
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Robert Fludd's 1618 "water screw" perpetual motion machine from a 1660 wood engraving. It is widely credited as the first attempt to describe such a device.
Something for Nothing (1940), a short film featuring Rube Goldberg illustrating the U.S. Patent Office's policy regarding perpetual motion machines (and the power efficiency of gasoline) Perpetual motion is the motion of bodies that continues forever in an unperturbed system. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an external energy source. This kind of machine is impossible, since its existence would violate the first and/or second laws of thermodynamics. These laws of thermodynamics apply regardless of the size of the system. Thus, machines that extract energy from finite sources cannot operate indefinitely because they are driven by the energy stored in the source, which will eventually be exhausted. A common example is devices powered by ocean currents, whose energy is ultimately derived from the Sun, which itself will eventually burn out.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).