Latin term for a
perpetual motion device. A
device (
thermodynamically
closed system) that achieves motion which can be used to do
work (i.e. a closed
exothermic reaction). Conceptually "weaker" versions (but essentially equivalent) are not-quite closed systems which exhibit
motion at a fixed rate despite
energy loss.
Forbidden by the first law of thermodynamics (conservation of energy) and the third law of thermodynamics (increase of entropy), depending on exact formulation. In other words, quite impossible; don't waste your time looking for one.
However, an excellent source of physics puzzles!