- 1a : continuing forever : everlasting <perpetual motion>
- b (1) : valid for all time <a perpetual right> (2) : holding (as an office) for life or for an unlimited time
- 2: occurring continually : indefinitely long-continued <perpetual problems>
- 3: blooming continuously throughout the season
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.