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 Foucault Pendulum Rotunda The pendulum in the rotunda of the Indiana State Museum reproduces the famous experiment first performed in Paris in 1851 by Jean Hbernard Leon Foucault, a French astronomer and physicist. Until a few hundred years ago, nearly everyone believed the earth was flat and the sun, moon, and stars rotated about it. Foucault is remembered as the first man to demonstrate the rotation of the earth without using anything outside of the earth - such as sun or stars - as a point of reference. A leading scientist of his day, Foucault also invented the gyroscope.

 After two earlier experiments, Foucault suspended a ball weighing 61 pounds on a steel wire 220 feet long from the dome of the Pantheon in Paris. Protruding from the ball was a pin adjusted to draw a mark through a ring of wet sand beneath the ball. Drawing the ball to one side, Foucault then released it. With each swing the pin made a mark in the sand and appeared to rotate in a clockwise direction, thus demonstrating, as he predicted, that the pendulum would revolve about 270 degrees in 24 hours and show the rotation of the earth. The pendulum seems to change its path during the day, but actually the floor beneath it changes by being twisted or moved counter-clockwise by the daily rotation of the earth. The same experiment in Indianapolis requires about 40 hours for a complete circle and approximately 24 hours for 240 degrees. This is due to the different latitudes and the length of the wire - the longer the wire, the slower the bob swings and the less impeded by friction with the air. The time varies at other locations on the earth, also. At the North Pole, it would turn a full 360-degree circle in 24 hours, while at the equator it would not turn at all. Since air resistance would normally stop the pendulum after a few hours, an iron collar is installed on the wire near the top of the Indiana State Museum=s glass dome. surrounded by an electromagnet, the collar is attracted to the magnet as the bob swings out. As the collar touches the magnet, the magnet shuts off allowing the wire to swing back. This keeps the pendulum going but does not alter the path of the pendulum's swing.

 The Indiana State Museum's Foucault Pendulum Facts: The bob is made of hollow bronze, weighing 212 pounds. The bob is supended on 85 feet of 1/8-inch standard aircraft control cable. The pendulum was installed in November 1968. The pendulum makes a swing of about 14 feet in 10 seconds.

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