This fascinating experimnet uses two tubes, one plastic and the other copper. First hold the plastic tube vertically, and drop a strong magnet down the tube. Measure the time taken for the magnet to fall through the tube and then repeat the experiment using the copper tube.
This experiment shows induced currents and relies on the magnetic field produced by a falling magnet in a tube acting so as to oppose the motion of the magnet so slowing down its rate of fall. (see diagram 1) The field of the falling magnet induces a current (shown red in diagram 1) in the tube which produces an opposing magnetic field to that of the magnet.
Using the copper tube a metre long takes over five seconds, compared with approximately 0.75 s when the same magnet is dropped down a plastic tube of the same dimensions. If the tube is cooled the resistance of the copper falls, the induced current is greater, and the magnet falls even more slowly. Allowing the magnet to slide down the tube when it is inclined at an angle to the vertical is almost more impressive - it takes nearly thirty seconds to emerge depending on the angle of tilt of the tube!
Lenz's law: Induced emf (ε) = minus the rate of change of flux in the circuit or the flux acts so as to oppose the change producing it. ε = -dφ/dt. Therefore the induced currents flowing round the tube produce a magnetic field along its axis, which slows down the rate of fall of the magnet.