A Perpetuum Mobile
(Latin for "forever moving") is an old dream of mankind: A machine that creates more energy than it receives from the outside. (A weaker version just keeps moving on and on, without creating new energy you could put in use.)
Obviously, a Sub-Trope
of Artistic License - Physics
. To be precise, a Perpetuum Mobile
contradicts the Second Law of Thermodynamics. Of course, this didn't stop some people from believing in a PM - they just insist that obviously, the Second Law has to be wrong.
Subtrope of Applied Phlebotinum
. A Mad Scientist
may work on this.
- In the second Jim Button book by Michael Ende, the protagonists invent it. Essentially, their version is based on a magnet which you can switch on and off, which pulls their locomotive.
- Gaston Lagaffe once invented one. It doesn't do much, it just hops around (and gets on his coworkers' nerves).