Many machines use magnetic brakes from the small to the gigantic. The analysis of the effect is simple in some ways and quite tricky in others. There are two ways of looking at magnetic braking, both of which are mentioned in the demonstration write-up. The basic idea is that when a conductor moves through a magnetic field, currents are induced that resist the motion. These are called Eddy currents, and the reduction in the kinetic energy of the conductor is equal to the resistive heating caused in the conductor by the induced Eddy currents. Another approach to explaining magnetic braking is that the Lorentz force acting on the electrons in the moving conductor acts to move the electrons outward, and the Lorentz force associated with that outward motion in the applied magnetic field serves to slow down the moving conductor. These two ways of thinking about magnetic braking are equivalent; that is, they make the same predictions. A couple of questions for reflection: If the conductor is a perfect conductor (no resistance, but not a superconductor), is there any braking effect? Also, can a magnetic brake by itself bring a moving conductor to a complete stop? Why, or why not?

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