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Foucault's pendulum a weight, usually a ball suspended by a wire that is attached at the ceiling with a joint that allows the weight to swing in any direction.

Foucault's pendulum is a weight, usually a ball suspended by a wire that is attached at the ceiling with a joint that allows the weight to swing in any direction.

The motion of this pendulum proves that the earth is rotating underneath the pendulum.  The angle of the rotation of the pendulum per hour remains fixed at any location and equals:

The motion of this pendulum proves that the earth is rotating underneath the pendulum.  The angle of the rotation of the pendulum per hour remains fixed at any location and equals: