Magnetic pendulum

HOW

1. Pull the string to one side until all the pendulums are evenly displaced.
2. Observe the movement of the pendulums.

WHY

The centres of the pendulums are strong magnets. A magnetic field is created around them. Under the pendulums are plates of various materials: copper, aluminium, brass, and stainless steel.

When a magnet moves over a metal plate, its magnetic field induces the eddy currents in it. They are the source of a magnetic field with such a direction and sense that the interaction of the magnetic fields has the effect of dampening the movement of the pendulums. The effect described is strongest for plates that are good conductors of electricity.