Foucault pendulum
- For the novel Foucault's Pendulum by Umberto Eco, See Foucault's Pendulum (book).
A Foucault pendulum, or Foucault's pendulum, named after the French physicist Jean Foucault, was conceived as an experiment to demonstrate the rotation of the Earth and the Coriolis force. It is a tall pendulum free to oscillate in any vertical plane and capable of running for many hours, and was first exhibited in 1851 from the ceiling of the Panthéon in Paris.
At almost any location on Earth -- except the equator -- it can be observed that the plane within which the pendulum swings slowly rotates. At either the North Pole or South Pole, the plane of oscillation of a pendulum rotates once per sidereal day (in essence, the pendulum remains in the same plane while the Earth rotates underneath it, as predicted by Newton's first law of motion). At other latitudes, the plane of oscillation of a pendulum rotates with an angular speed proportional to the sine of its latitude; thus one at 45° rotates once every 1.4 days and one at 30° every 2 days.
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