The Foucault Pendulum is named for the French physicist Jean Foucault (pronounced "Foo-koh), who first used it in 1851 to demonstrate the rotation of the earth. It was the first satisfactory demonstration of the earth's rotation using laboratory apparatus rather than astronomical observations.

Imagine you are in a museum located at the north pole and that the museum has a Foucault Pendulum suspended from the ceiling at a point exactly over the pole. When you set the pendulum swinging it will continue to swing in the same direction unless it is pushed or pulled in some other direction. (This is due to a basic law of nature called Newton's First Law.) The earth, on the other hand, will rotate once every 24 hours underneath the pendulum. Thus if you stood watching the pendulum, after a quarter of an hour or so, you would be likely to notice that the line of the pendulum's swing has changed to a different direction. This would be especially clear if one marked the position of the line of swing in the morning and had the pendulum knocking down pegs arranged in a ring at the center.