The Magnetic Pendulum
Colour by winner, find a fractal
Suspend an iron pendulum over three magnets arranged in a triangle. The motion is deterministic — Newton's laws plus magnetic attraction plus a touch of friction — and yet the question 'which magnet does it end up over?' has no smooth answer. Colour each starting position by its eventual winner and you uncover a basin-of-attraction fractal: red, green and blue regions interlocked at every scale, with every boundary point a frontier between all three magnets at once. Determinism without predictability.
