We all know the truth of earth rotation, but never had a man proved it like Foucault. He just showed us the phenomenon of the earth rotation by a simple experiment- Foucault Pendulum, which can make us see the fact by our own eyes.
In 1851, the French physicist Léon Foucault placed a pendulum device in the Paris National Cemetery. The length of the pendulum was 67 meters. An iron ball was at the bottom of the pendulum weighing 28 kilograms, and a slender needle was inserted under the iron ball. It turned out that Foucault was to prove the earth’s rotation. He imagined that when the pendulum swings, it will maintain a fixed swing direction without external force. If the earth is rotating, then the ground below the pendulum will rotate, and the pendulum suspended in the air will have a tendency to keep the original swing direction. For the observer, the swing direction of the pendulum will change with respect to the ground. The original idea is perfect, but the experiment is not easy to set. Because the change in the direction of the pendulum is subtle, a slightly stronger stream of air will affect the experimental results. Foucault finally chose the test site in the Paris Observatory, and placed a sand table under the pendulum. When swinging, the tip of the pendulum marks a track on the sand table, thus recording the direction of the swing. The results of the experiment are in perfect agreement with Foucault’s ideas (Oprea, 1995). The pendulum swings show a slow, continuous rotation from east to west. Foucault’s demonstration directly proves that the earth rotates from west to east.
It was found that at the poles of the earth, Foucault’s pendulum swings 24 hours, while at the equator, the pendulum has no rotation; in the region between the poles and the equator, the pendulum’s rotation speed falls in between. Below the equator the apparent rotation begins again, but in the opposite direction.
As mentioned earlier, the speed at which Foucault pendulum rotates at different points in the Earth is different. This shows that the line speeds at different locations on the Earth’s surface are different. Therefore, Foucault can not only verify the rotation of the Earth, it can also be used to find the latitude of the place.