In 1851 Léon Foucault suspended a 28 kg brass-coated lead ball from the dome of the Panthéon in Paris. His purpose was to demonstrate the rotation of the earth by showing that the pendulum, which swings in one fixed plane, appears to move at a rate of 11 degrees per hour. In reality, the observer, the floor and the whole earth are rotating while the pendulum remains in its constant plane.
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