Pendulum

Foucault Pendulum- Invented by Jean Foucault (French physicist) in 1851. It gave the first direct proof that the Earth rotates on its axis. The Observatory pendulum is a 240-pound brass sphere suspended from a 40-foot steel wire. Once started, it continues to swing in the same direction. A ring magnet above the ceiling keeps the pendulum in motion without influencing the direction of its swing.

 

Every ten minutes or so the pendulum knocks over a peg, but it's not the pendulum that has moved: the earth has moved the peg into the path of the pendulum. The pendulum is disconnected from the turning of the earth, and the earth rotates beneath it, making it look as if the pendulum is changing the direction of its swing.

 

At the north and south poles, it takes 24 hours for a complete circle of pegs to be moved into the pendulum's path. The closer it is to the equator, the more slowly the pegs rotate. At the

equator itself, there is no apparent shift, and no pegs would be knocked down. The pit here is divided into 42 hourly divisions, which is how long it takes the pendulum here to go through the full circle. Griffith Observatory. DSC-5253

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