Perpetuum mobile

Looking at this toy you get the impression it is moving with no apparent cause ad infinitum! It seems that it acts like a perpetuum mobile, a machine that, once set in motion, would remain in motion infinitely if it was placed in perfect vacuum and we could ignore friction connected with movement.

The existence of perpetuum mobile is excluded by the basic laws of physics. In the case of our toy, there is a device in its platform powering the pendulum by means of magnetic force which itself is powered by a 9-volt battery. One coil, hidden inside the platform, produces electricity from the movement of the pendulum. A simple electronic system powers the other coil with the current going in such a direction so as to push the pendulum away. This can be compared to a parent pushing a child on a swing. You have to push at the right moment and the push can't be too strong.

There are some machines which, at first glance, operate like a perpetuum mobile. A meticulously constructed mechanic clock can go on without winding even for a few hundred years.