by In 1851, French physicist Léon Foucault provided experimental evidence of the Earth’s rotation using a pendulum. Although Foucault is best known for this ingenious experiment, he also made several important contributions to physics, including the discovery of eddy currents and the measurement of the speed of light. Foucault is one of the 72 scientists whose names are engraved on the sides of the Eiffel Tower.
At the Arts et Métiers art museum in Paris, visitors can see Foucault’s pendulum experiment in action twice a day. The setup consists of a 17-meter-long metal cable suspended from the ceiling with a brass-coated lead ball attached to the lower end. As the pendulum swings, it gradually knocks over wooden pins arranged on a round table below, demonstrating the rotation of the earth.
According to Maela Levigne of the Arts et Metiers Museum, “The pendulum begins to swing in the direction in which it is thrown without any noticeable delay. The period of oscillation (of this pendulum) is between seven and eight seconds. Between each oscillation, the Earth shifts by one millimeter.”
She explained that even though the pendulum never leaves its plane of oscillation, it can still knock over the pins because the Earth shifts beneath it.
What moves is the Earth, which shifts relative to the plane of oscillation of the pendulum. “By shifting, the Earth moves the table, which in turn moves the cones lying on the table. They then come into contact with the pendulum and eventually fall.”
Foucault’s Pendulum
The Foucault pendulum consists of a large, heavy weight or bob that hangs from a long wire and can swing in any direction.
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