Used to show that when a conductor is exposed to a changing magnetic field, this causes a flow of current, eddy current, which produces an induced magnetic field to oppose the change.
|Variable gap magnet|
Let the 3 pendulums swing between the gap magnet one at a time and observe the difference. The solid pendulum stops as it goes between the variable gap magnet. The slotted pendulum oscillates freely. The third one with slits oscillates then stops.
You can also drop a small bar magnet inside a copper pipe and the student will see that it takes more time for the bar magnets to reach the ground due to the force generated from the eddy current.