Question

how does an eddy current brake stop something moving?

Answer 1

Suppose we have a railroad train that's actually a huge solid block of copper mounted on wheels. Let's say it's hurtling along at high speed and we want to stop it. We could apply friction brakes to the wheels—or we could stop it with eddy currents. How? What if we put a giant magnet next to the track so the train had to pass nearby. As the copper approached the magnet, eddy currents would be generated (or "induced") inside the copper, which would produce their own magnetic field. Eddy currents in different parts of the copper would try to work in different ways. As the front part of the train approached the magnet, eddy currents in that bit of the copper would try to generate a repulsive magnetic field (to slow down the copper's approach to the magnet). As the front part passed by, slowing down, the currents would start generating an attractive magnetic field that tried to pull the train back again (again, slowing it down). The copper would heat up as the eddy currents swirled inside it, gaining the kinetic energy lost by the train as it slowed down. It might sound like a strange way to stop a train, but it really does work. You'll find the proof of it in many rollercoaster cars, which use magnetic brakes like this, mounted on the side of the track, to slow them down.