Question Is gravity a perpetual motion machine?
The moon makes the tides, and machines can convert the tides into energy. Doesn't that sound like a perpetual motion machine?

Best Answer Perhaps. I think this search will be helpful to you.

Question How is perpetual motion related to anti-gravity?
On another question some claimed that an anti-gravity machine would require perpetual motion. I would like to know why and/or how.

Best Answer it wouLdn't but a perpetual motion machine might require anti-gravity, or atleast very LittLe gravity

Question Would it be possible to achieve perpetual motion in space (no gravity or friction)?
To my knowledge, the problems with achieving perpetual motion on Earth are friction and gravity. The friction takes energy away from the object by resisting motion, and gravity takes away energy by pulling objects toward each other. Since space is a vacuum, there would be no air resistance or other friction. Also there would no gravity in distant space, as there would be no other objects to influence it. So then it seems possible that in space, such perpetual motion, and theoretically unlimited energy, is possible to achieve. Any thoughts?

Best Answer The problem is that the term 'perpetual motion' has changed its meaning somewhat. It has come to mean a system from which you can extract energy without having to put energy into that system. There's no particular (Newtonian) objection to the idea of shooting an object off into deep space with as much kinetic energy as you care to give it and expecting it to keep going. The trouble is that if you try to use any of that energy, then *you* are the thing 'influencing' it and slowing it down. There's no unlimited energy there I'm afraid.