Earth's rotation Foucault in 1851, which consisted of a lead-filled brass sphere suspended from the top of the Panthéon in Paris. Because of the Earth's rotation under the swinging pendulum, the pendulum's plane of oscillation appears to rotate at a rate depending on latitude. At the latitude of Paris the predicted and observed shift was about clockwise per hour. Foucault pendulums now swing in museums around the world. Earth's rotation period relative to the Sun (solar noon to solar noon) is its "true solar day" or "apparent solar day". It depends on the Earth's orbital motion and is thus affected by changes
Foucault pendulum Earth, "F" is the component of the Coriolis force in the "x"-direction and "F" is the component of the Coriolis force in the "y"-direction. The restoring force, in the small-angle approximation, is given by Using Newton's laws of motion this leads to the system of equations Switching to complex coordinates , the equations read To first order in Ω/"ω" this equation has the solution If time is measured in days, then and the pendulum rotates by an angle of −2π sin("φ") during one day. Many physical systems precess in a similar manner to a Foucault pendulum. As early as 1836,