Foucault pendulum

A long, freely swinging pendulum whose swing plane appears to rotate relative to the ground, demonstrating Earth’s rotation.

Coriolis effect: The apparent deflection of moving objects described in a rotating reference frame. Earth’s rotation makes the pendulum’s nearly fixed swing plane appear to turn relative to the floor.
Léon Foucault: A French physicist known for experiments demonstrating Earth’s rotation and measuring the speed of light. He devised the pendulum demonstration and presented it in Paris in 1851.
Simple pendulum: An idealized mass suspended from a pivot and swinging under gravity. The Foucault pendulum applies this familiar motion on a scale large enough to reveal Earth’s rotation.
Griffith Observatory: A public observatory in Los Angeles opened in 1935. Its Foucault pendulum demonstrates Earth’s rotation inside a widely visited science institution.
Coriolis force: A fictitious force used to describe motion in a rotating reference frame. It is a frame-dependent description of the deflection, while the pendulum’s inertial swing needs no physical sideways force.
Inertial frame: A reference frame in which objects obey Newton’s laws without fictitious forces. The swing plane stays nearly fixed when described against an inertial frame.
Panthéon, Paris: A Paris monument originally built as a church and later used as a mausoleum. Foucault’s celebrated public pendulum demonstration took place beneath its dome.
Newton's laws of motion: Three foundational laws relating motion, forces, and momentum in classical mechanics. The pendulum’s persistence in its swing direction follows from Newton’s account of inertia.
United States Capitol Rotunda: A domed ceremonial hall at the center of the United States Capitol. A Foucault pendulum installed there makes Earth’s rotation visible in a civic landmark.
Foucault gyroscope: A gyroscope experiment demonstrating Earth’s rotation through the orientation of a spinning rotor. It tests the same planetary rotation with a spinning rotor rather than a swinging mass.

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