In conductors, electric currents are generated whenever there is a changing magnetic field. These currents generate their own magnetic field, which opposes the magnetic field which generates them. If a strong magnet was dropped onto a piece of aluminum, the magnet once dropped generates a current in the aluminum because as the magnet gets closer, the field gets stronger at the position of the aluminum. This generates an electrical current, which creates its own magnetic field in opposition to the magnet's field, acting on the magnet, and slowing it down.

Here's where it starts getting really interesting. The generated magnetic field will be notably weaker than the field of the dropped magnet, because the current is subject to electrical resistance. But what if we used a superconducting material, where there is zero electrical resistance, the two magnetic fields should equal eachother, right?

This is called the Meissner effect. This video shows an experiment of a strong magnet being put on top of a YBCO superconductor. All superconductors need to have their temperature dropped dramatically in order to to hit the superconducting threshhold known as a transition temperature. Typical transition temperatures are below 10 kelvin. YBCO is a unique material known as a high temperature superconductor, meaning that it can be cooled to its transition temperature with liquid nitrogen (about 70 kelvin).