Foucault Pendulum

Due to the pendulums inertia, once started, it will oscillate in the same plane forever. However, since the pendulum is on Earth which rotates about its own axis, from our rotating point of view the pendulum’s plane of oscillation seems to be what’s rotating. The period of rotation depends on your latitude too: at the North Pole the pendulum rotates once a day but at the equator it doesn’t rotate at all!