At the Franklin Institute Science Museum years ago, they had a huge (2 foot diameter? More?) copper disk attached to a crank suspended in the gap of a big-ass electromagnet. The idea was you spun the crank, and then operated a foot pedal that applied current to the electromagnet, which braked the wheel with eddy currents.
The disk had slotted sectors, so you could tell that the braking effect was less when those sectors were in the gap.
I don't know if the exhibit survived the themparkification of fi.edu... I hope so but somehow I doubt it.
There's a similar demo at the Exploratorium in San Francisco - you can drop disks of different materials (and with different cutouts) through the electromagnet and see the different rates at which they drop. I recall it also had a thoughtful warning sign instructing folks to keep their (magnetic stripe) BART cards away from the electromagnet!
The disk had slotted sectors, so you could tell that the braking effect was less when those sectors were in the gap.
I don't know if the exhibit survived the themparkification of fi.edu... I hope so but somehow I doubt it.