Algodoo

Weird. As the simulation frequency getting larger, the box moves slower.
To prove that the belt isn't moving at all, I used script to grey out the block as soon the laser shines on each individual rope links.
You can always stop the motor to prove that it only moves whenever it spins.
To avoid isodecryptor's problem, I'll let everyone free to point out the misconception of this mechanism. I won't be offended.