In Léon Foucault’s 1848 pendulum experiment, the changing swing plane demonstrated Earth’s rotation.
A long pendulum tends to keep swinging in nearly the same plane because of inertia. As Earth rotates beneath it, an observer on the ground sees the plane gradually turn relative to the floor.
The apparent rate depends on latitude. It is fastest at the poles, where a complete apparent rotation takes about one sidereal day, and it is zero at the equator. Paris, where Foucault demonstrated the effect, lies at an intermediate latitude.
The pendulum does not need to be driven around in a circle. Its changing orientation is an observational effect caused by the rotating reference frame of Earth, making the demonstration a vivid mechanical proof of planetary rotation.