I've been teaching about eddy currents induced in metal by changing magnetic fields, Trouble is, not many students seem to know what an eddy is. I found some eddies on the River Wear near Durham. They are shortlived mini-whirlpools in the water. In the same way, an eddy current is a circular current loop that's really going nowhere. But it does act as a mini-electromagnet which can cause problems.
