What about free energy?

There are many sites describing and selling "free energy" sources using strong static magnets only. I do not want to bust this myth, and say that a device like that can not work, and can not actually transform energy.  However the sad fact according to the current laws of physic is, that nothing in the world is for absolutely free. Those who claim inventing free energy are stating inventing perpetuum mobile.

The ultimate perpetuum mobile

This joke might reveal what the contradiction of perpetuum mobile is.

The rabbi is asked one day:

- Is it true that if I let fall a slice of bread with butter on the top, it will fall on the side with the butter?

- Yes, answers the rabbi.

- And is it true that if a cat is falling it always falls on the feet?

- Yes.

- So what happens if I let fall a cat standing on the top of the butter bread?

But really, what happens? Let's suppose that both statements are true. Both items should fall on the side where they are glued together. So the answer is simple: it should never fall, and keep flying. And we can say that this is the greatest discovery of all times.