How do those little pendulums work?

[davidhorman]

I have a couple of those "executive toy" pendulum things - like a couple of dolphins, or concentric circles. They swing back and forth, and in the base is a magnet powered by a 9V battery.

How does the magnet keep the pendulum swinging? I'm pretty sure there are no moving parts in the base.

David

 

[RCNelson]

The part that swings is a magnet.

In the base there is a wire coil which will produce a small voltage as the swinging magnetic part passes over the coil.

This voltage triggers a circuit which makes a pulse of current through an electromagnet coil.

The magnetic field pulse emanating from the electromagnet coil nudges the swinging magnet so that it can keep swinging forever (or until the battery dies).