Lenz's law

One of the first laws that is usually studied in high school Physics courses is Faraday-Lenz's law. I remember our teacher telling us that Michael Faraday discovered one of the most important laws in electromagnetism, which in fact relates electric to magnetic effects - and that Lenz's contribution was only the minus sign!-. I also remember our Electromagnetism Professor at the UPV-EHU entering the classroom with a copper tube and two seemingly identical pieces of metal and doing the magic that you can see in this video!

Faraday's law states that the variation of a magnetic flux through a conductive coil will induce an electromotive force in the latter. Emil Lenz realised that this electromotiv force will oppose to the magnetic flux variation (so he is responsible for the minus sign in Faraday's law, a.k.a. Faraday-Lenz's law).

In order to reproduce this astonishing effect you will only need a metallic (but non-magnetic! that is, essentially not made out of iron) tube and a small magnet (and if you want the full show, a small metallic chunk, this time it can be a piece of iron).