Magnetic Braking
Drop a magnet down a metal tube and, instead of falling freely, it drifts down slowly — the moving magnet induces electric currents in the metal that create a drag force opposing its own fall.
Try looking inside the copper tube from the top and you will notice something interesting.
Additional Information
This only works with a conductive but non-magnetic metal like copper or aluminum — the tube itself isn’t magnetic, but it still reacts to a moving magnetic field.
The induced currents are called eddy currents, and the effect is known as Lenz’s law: induced currents always oppose the change that created them. In the plastic tube, no such currents are produced, so the magnet falls almost normally under gravity.
Roller coasters and some elevators use this exact same eddy-current effect as a smooth, contact-free braking system.