I found how to make a perpetual motion machine! (just joking, keep reading! :tongue2:) We just saw what they are in my thermodynamics class, and if I understood correctly, it represents the only heat-to-work conversion machine not (theoretically) in violation of the second law. And this solution is that q=w=0 (the heat absorbed and the work done are both 0). So it's just this thing that gets back to exactly its original macroscopic state ([itex]\Delta S=0[/itex]) after a certain "cycle" or "period". But what goal does it have? It must have one if hundreds of people are submitting perpetual motion machines ideas to the patent office every year.