There are fluids with special properties, including being susceptible to magnetism, and proving an almost frictionless surface while in the magnetic field.

Someone a while ago worked out that the correct designed gadget would produce power, not perpetual motion, but normal EM generated power converting input motion energy which works because of the low losses due to the fluid.

Some current (sorry!) applications include using wave motion to power sensor buoys.

Breaks no 'Laws of Nature'.