OCC's Foucault Pendulum. A live demo proving Earth spins beneath our feet. Suspended in the planetarium lobby, it swings and slowly alters direction, knocking down pins

A Foucault pendulum is a simple, heavy weight suspended on a long wire that swings in a constant plane. As it swings, the Earth rotates underneath it, making the path of the pendulum appear to slowly shift in a circle. It was first used by French physicist Léon Foucault in 1851 as a direct visual proof that the Earth rotates on its axis.