A magnetic race
Choose one pipe and move the magnet on the pipe upwards. Drop the magnet and watch how it moves. Conduct that experiment with different pipes and compare the results.
Turn the frame with the pipes so that all the magnets are up. Watch how they race.
How it works
A falling magnet induces the so-called eddy currents in the pipes. These currents generate a magnetic field which repels the field of the magnet. As a result of interaction between magnetic fields of the magnet and eddy currents, the magnet does not fall freely. The effect of slowing down the fall is proportional to the magnitude of eddy currents. The magnitude of eddy currents depends on the electrical conductivity of a particular pipe. The pipes are made of copper, aluminium, brass and stainless steel.
Eddy currents are generated because of electromagnetic induction. This phenomenon, discovered in 1831 by an English physicist Michael Faraday is the most common form of generating electricity.