The Significance of Foucault's Pendulum

In 1848, Foucault had noticed an interesting aspect in the behavior of pendulums. When you turn the point from which the pendulum is hung, the movement of the pendulum is not disturbed. It wasn't until 1851 that Foucault would use this to demonstrate the Earths rotation in the Panthéon in Paris. He hung a 28 kg brass bob from the ceiling using a 67 m long cable. On the floor, there was a wooden platform with a layer of sand that the pendulum would trace its motion in. This made the deflection of its motion more evident. Foucault had reasoned that the pendulum appears too be rotating because the Earth is rotating beneath, while not affecting the pendulums motion. Not only did this demonstrate the Earth's rotation, but the Coriolis Effect as well.

Retrieved from http://ian.umces.edu/blog/2011/03/17/leon-foucault-science-communicator/

The  Coriolis Effect is not felt to be the same at all parts of the world. The effect of the Coriolis effect is greatest at the poles, and at its least at the equator. This is why Foucault's pendulum would not work at the equator, but its motion would experience deflection of the greatest degree at the poles. Below is a graph showing the effect of the Earth's spin on the pendulum's motion depending on the latitude at which the the pendulum is located. At the equator the pendulum will not be affected at all. At the South Pole, the pendulum will make a full rotation in the clockwise direction. At the North Pole, the pendulum makes a full rotation in the counter clockwise direction. These transformations take an entire day.

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The image above is an example of Foucault's Pendulum at work and the apparent deflection it goes through.