Eddy current brake - coolest one known

People, Check this out in google/wikipedia.
Eddy current brake.

 

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I agree, they are just cool. We have a simple little experiment in the first year physics labs at my university, which we bring out to amuse the public on open days. Basically it is a pendulum arm with a flat metal plate at the bottom oriented like a swinging axe death trap, with another pendulum swinging on the same axis aligned right next to it, except the plate attached to this one has a series of slices taken out of it so it looks a little like a comb. There is a fairly powerful pair of magnets sitting either side of the lowest point of the pendulum arc. When you swing the pendulums it demonstrates that big eddy currents get you nice strong braking in the solid plate, while the slices cut in the second plate prevent such nice big current loops from forming so there is very little braking. It is cool.

 

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