12 Facts About Foucault pendulum

Foucault pendulum or Foucault's pendulum is a device named after French physicist Leon Foucault, conceived as an experiment to demonstrate the Earth's rotation.

The Foucault pendulum was introduced in 1851 and was the first experiment to give simple, direct evidence of the Earth's rotation.

The original, now damaged Foucault pendulum bob is displayed in a separate case adjacent to the current Foucault pendulum display.

An exact copy of the original Foucault pendulum has been operating under the dome of the Pantheon, Paris since 1995.

At either the Geographic North Pole or Geographic South Pole, the plane of oscillation of a Foucault pendulum remains fixed relative to the distant masses of the universe while Earth rotates underneath it, taking one sidereal day to complete a rotation.

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Foucault pendulum requires care to set up because imprecise construction can cause additional veering which masks the terrestrial effect.

The initial launch of the Foucault pendulum is critical; the traditional way to do this is to use a flame to burn through a thread which temporarily holds the bob in its starting position, thus avoiding unwanted sideways motion .

Notably, veering of the Foucault pendulum was observed already in 1661 by Vincenzo Viviani, a disciple of Galileo, but there is no evidence that he connected the effect with the Earth's rotation; rather, he regarded it as a nuisance in his study that should be overcome with suspending the bob on two ropes instead of one.

Besides air resistance the other main engineering problem in creating a 1-meter Foucault pendulum nowadays is said to be ensuring there is no preferred direction of swing.

The inner gimbal of the Foucault pendulum gyroscope was balanced on knife edge bearings on the outer gimbal and the outer gimbal was suspended by a fine, torsion-free thread in such a manner that the lower pivot point carried almost no weight.

At least three more copies of a Foucault pendulum gyro were made in convenient travelling and demonstration boxes and copies survive in the UK, France, and the US.

The Foucault gyroscope became a challenge and source of inspiration for skilled science hobbyists such as D B Adamson.