Eddy Currents, Magnetism, Gearless Magnet Bike
https://www.youtube.com/watch?v=yCh9Plk7DSw “Hey that’s pretty neat to learn about the alternating polarity creating a greater resistance. I didn’t think of that. You could print a little cube grid that holds multiple magnets with opposing fields and probably get a much more impressive slow down when dropping it down a pipe.”