Steve Mould explains and extols the virtues of a wonderfully-designed perpetual motion simulator (previously at BB) crafted by William Le. He even commissioned a transparent version that shows the clever and surprisingly complex interior workings—and the batteries!—that make the illusion possible.
Perpetual motion is impossible but this device simulates what it might look like and it uses some really clever engineering.
William Le is the original creator of this widely knocked-off design, so if you like it you should buy one from him on Etsy. I really like this Escher-like marble run.
