Show two tubes of the same size, one made of copper or aluminium and one made of plastic (not telling the public what material they are made of).

Drop a magnet through the aluminium or copper tube. The magnet falls much more slowly than if it were in free fall.

Drop the magnet again but now bring a ferromagnetic ring on your finger close to the tube. The magnet stops falling.

Repeat but now with a plastic tube, the magnet will fall in free fall.

To perform this trick we can ask for a volunteer to run a race, whoever takes the longest to get through the tube wins. We give the metal tube to the volunteer and keep the plastic one, count to 3 and drop the magnet at the same time. We congratulate the winner for managing to slow down the fall.

This magic trick is related to the Lenz's Law, a fundamental law of electromagnetism that explains the direction of an induced current in a conductor in response to a changing magnetic field, with the induced current creating its own magnetic field to oppose the change. This law is named after the Russian physicist Heinrich Lenz, who formulated it in the mid-19th century. 

Lenz's Law tells us that the direction of the induced current is such that it opposes the change in the magnetic field that caused it. In other words, the induced current creates a magnetic field that counteracts the change in the original magnetic field.

A common example used to illustrate Lenz's Law is the experiment with a magnet and a conducting tube (e.g., a copper or aluminium tube). When you move the magnet towards the tube, the changing magnetic field induces an electric current in the tube. According to Lenz's Law, the induced current creates a magnetic field that opposes the motion of the magnet.

This opposition between the induced current's magnetic field and the original magnetic field is the reason why objects, like the magnet, experience resistance or "drag" when moving through conductive materials.