Foucault’s Experiment

Foucault's Pendulum: A Visible Proof of Earth's Rotation

The concept of Earth spinning on its axis, completing a full rotation roughly every 24 hours, is a cornerstone of modern astronomy. While the Earth's rotation is invisible to our naked eye, a clever experiment devised by French physicist Léon Foucault in 1851 provided undeniable visual proof. This experiment, now famously known as Foucault's Pendulum, has become an iconic demonstration of Earth's motion.

The Experiment:

The setup is remarkably simple. A heavy metal ball, typically several kilograms in weight, is suspended from a long, fine wire. The wire is ideally attached to a fixed point, high above the ground, allowing the ball to swing freely in any direction.

Once set in motion, the ball oscillates back and forth, tracing a plane of vibration. The magic happens when we observe this plane over time. Instead of staying fixed, the plane of vibration appears to slowly rotate. This rotation is not due to any external force acting on the pendulum but is a direct consequence of the Earth rotating beneath it.

The Science Behind the Rotation:

The key to understanding Foucault's pendulum lies in the concept of inertia. As the Earth rotates, the pendulum's plane of vibration tends to maintain its original orientation relative to the distant stars (a frame of reference that is considered to be at rest). However, since the Earth is rotating beneath the pendulum, the plane of vibration appears to rotate relative to the Earth’s surface.

The Rotation's Dependence on Latitude:

The rate of rotation of the pendulum's plane is not constant but depends on the observer's latitude:

• At the poles: The plane of vibration completes a full rotation in one sidereal day (23 hours, 56 minutes), coinciding with Earth's rotation.
• At the equator: There is no apparent rotation of the plane of vibration as the pendulum's motion stays perfectly aligned with the Earth's surface.
• At intermediate latitudes: The rotation time of the plane is proportional to the sine of the latitude. For example, at 45° latitude, the plane will complete one rotation in approximately 34 hours.

Foucault's Pendulum: A Legacy of Scientific Wonder:

Foucault's Pendulum, besides being a beautiful and elegant experiment, has become a cultural icon. It serves as a powerful reminder of the constant, yet invisible, motion of our planet.

Large Foucault's pendulums are on display in museums and universities around the world, serving not just as scientific demonstrations but also as mesmerizing art installations. They invite us to pause and reflect on the intricate workings of our universe, proving that even seemingly simple objects can reveal profound truths about our world.