Perpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not.

There is undisputed scientific consensus that perpetual motion would violate either the first law of thermodynamics, the second law of thermodynamics, or both. Machines which comply with both laws of thermodynamics but access energy from obscure sources are sometimes referred to as perpetual motion machines, although they do not meet the standard criteria for the name.

Despite the fact that successful perpetual motion devices are physically impossible in terms of our current understanding of the laws of physics, the pursuit of perpetual motion remains popular.
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