The Pendulum Doesn't Turn - The Earth Does!
First exhibited in 1851 at the World’s Fair in Paris, the Foucault Pendulum (named after Jean Bernard Leon Foucault, the French physicist who invented it) is a visual demonstration of the Earth’s rotation.
Throughout the day, the direction of the pendulum’s swing appears to change. Actually the Earth is turning under the pendulum as it swings. At Houston’s latitude (30° N.) the pendulum will precess through 180° or halfway around each day. During this time, it will knock down all of the pins.
The time required for the pendulum to complete its swing is a function of its length. Swinging from a cable over 60 feet long, the pendulum’s period is just over 7 seconds. The pendulum receives the energy needed to keep swinging from a magnet surrounding the cable at its top. As the pendulum reaches the middle of its swing, it closes a circuit that activates the electromagnet. The magnet pulls the cable away from the center position. The pendulum keeps on swinging as the world turns below.