What it shows:
A sheet of aluminum falls slowly between the poles of a magnet because induced currents in the sheet set up magnetic fields which oppose the motion.
How it works:
As the aluminum sheet falls between the poles of the magnet, eddy currents are induced in the metal. These currents set up their own magnetic fields, which through Lenz's law oppose the change that caused them. As the cause is gravity pulling the sheet to Earth, the sheet decelerates as it passes between the poles of the magnet, only to accelerate again when it clears the magnetic field.
Setting it up:
Mount the Magnetron horseshoe magnet on the edge of the bench, on its side. The aluminum sheet is 10×30cm, with a luminous orange tape surround for visibility.
A good companion for the Eddy Current Pendulum and Magnetic Levitation demos.