Motor which operate solely on magnet and gravity?

[Harmony]

I received an assignment from my professor which sounds like follow:

"Suggest a motor which operates only on magnets and gravitational force."

While I did make a search online and found some model which seems to work, I am sill a little skeptical (There are videos online, but none of them are authentic). Are there any design which full fills such requirement, and has been verified? I was told that such machine would not violate the 2nd Law of Thermodynamics because the magnet itself is the energy source. Can anyone verified / debunk this?

Thanks in advanced.

[mgb_phys]

Without any external energy input - it's going to be tricky.
Otherwise it's quite easy.
1, Attach plastic paddle wheel to electric motor.
2, Stand above it
3, Drop magnets onto paddle wheel.
4, Motor turns - generates electricity

[Bobbywhy]

You may try putting a permanent magnet on a Focault pendulum.
As the pendulum precesses the magnetic interacts with the earth's magnetic field and adds kinetic energy!

[Ivan Seeking]

It not only violates the second law, it also violates Ivan's law. :biggrin:

Perpetual motion/free energy discussions are banned because it [such a motor] would violate the second law.

There is a small amount of energy stored in the field of a magnet, but only a very little bit. And there is no way to switch it on and off as we would do for a motor using electromagnets, brushes, and a rotor.