Perpetual motion is the motion of bodies that continues forever in an unperturbed system. A perpetual motion machine is a hypothetical machine that can do work infinitely without an external energy source. This kind of machine is impossible, as it would violate either the first or second law of thermodynamics or both.

Will a perpetual motion machine ever be invented?

Almost as soon as humans created machines, they attempted to make "perpetual motion machines" that work on their own and that work forever. However, the devices never have and likely never will work as their inventors hoped.

Why can perpetual motion not work?

The first law of thermodynamics says that energy can't be created or destroyed. You can't get out more energy than you put in. That rules out a useful perpetual motion machine right away because a machine could only ever produce as much energy as it consumed.