This robustly constructed inertia demonstrator works reliably every time and is a great improvement on traditional versions of this classic experiment. A steel ball rests on a thin metal card on top of a pillar, and a spring-loaded catch is mounted next to the pillar. When the catch is released, a piston strikes the edge of the metal card sharply. The card flies out from under the ball, which remains in place on top of the pillar due to its large inertial mass. The card is tethered to the aluminum base for easy recovery after the experiment.