http://en.wikipedia.org/wiki/Conservation_of_energy

Another consequence of this law is that perpetual motion machines can only work perpetually if they deliver no energy to their surroundings. If such machines produce more energy than is put into them, they must lose mass and thus eventually disappear over perpetual time, and are therefore impossible.

You can't just create energy out of nothing. Now about that warp drive on Moxie's car...

-Bal.