So you need to Pick a problem: keep a coaster on its track

The train has no engine.

1. So a chain drags it up the first hill, and that height is all the energy it gets.
2. But if the chain snapped, you'd roll backward.
3. So anti-rollback dogs drop in behind each tooth of a ratchet. That's the clicking you hear.
4. But over a crest, the track drops away faster than you fall, and the train wants to lift off.
5. So the wheels grab the rail three ways: on top, on the side, and underneath.
6. But now you have to slow it without touching it.
7. So copper fins slide between magnets, stirring up eddy currents that push back.

A roller coaster isn't sitting on its track. It's wrapped around it.