[RedDevil]

Another fun test of induced electromagnetism:
If you have a copper pipe, like an old piece of plumbing, and a magnet that fits inside it - hold the tube vertical and drop the magnet in.
It will take several seconds to descend through the tube!

The reason is that the magnetic field induces a current going round the tube, creating a magnetic field opposing that of the falling magnet. As the copper has some electrical resistance the currents die down, the field drops off and the magnet sinks down, but by doing so increases the magnetic field further down the tube.

Now if you cut a slit alongside the tube so the current can't go round you'll see in that part it will hardly impede the magnet at all. There will still be local currents, but no longer the strong one going round. It will still impede the magnet slightly, but the difference is enormous.

This principle is used in frictionless shock absorbers. By replacing the tube with coils and controlling the current one can control the level of dampening and venture into active suspension or even temporary ride height adjustment.