What is a Foucault Pendulum?
A Foucault Pendulum is a tall pendulum designed to swing freely in any vertical plane, visibly demonstrating the rotation of the Earth. Suspended from a fixed point, its plane of swing appears to slowly rotate relative to the floor, even though the pendulum itself maintains a constant plane of oscillation in space due to inertia.
How It Works: Inertia and the Coriolis Effect
The pendulum's bob, due to its inertia, strives to maintain its original plane of swing in relation to the distant stars. As the Earth rotates beneath it, an observer on the ground perceives the pendulum's swing plane as rotating. This apparent rotation is a manifestation of the Coriolis effect, influenced by the observer's changing position on the spinning Earth.
A Classic Demonstration Setup
Typically, a Foucault Pendulum consists of a heavy bob suspended by a very long wire from a high ceiling, often in large public buildings like museums or universities. A common demonstration involves placing small pegs in a circle around the pendulum's base, which the pendulum's bob gradually knocks over, visually confirming the subtle shift in its swing plane over time.
Proving Earth's Rotation
Historically, the Foucault Pendulum provided one of the most direct and compelling experimental proofs that the Earth rotates on its axis. It offered a tangible, observable demonstration of this fundamental astronomical phenomenon from Earth's surface, making the abstract concept of planetary rotation concretely evident to scientists and the public alike.