Foucault Pendulum Overview

• Ancient Greek astronomers explained the apparent motion of the stars on the sky by assuming that the stars were located on a giant "Celestial Sphere" that spun once per day, with the spherical Earth sitting stationary at the center of the Celestial Sphere..
• In the 16th century, Nicolaus Copernicus proposed that it was the Earth that rotated, not the Celestial Sphere. Copernicus' theory was initially rejected because the idea of a moving Earth did not fit with the understanding of motion at that time.
• New ideas about physics and motion led to attempts to experimentally detect the Earth's rotation, but these attempts were largely unsuccessful and the idea of a rotating Earth eventually became accepted for theoretical reasons, not because of any direct evidence.
• In 1851 Leon Foucault devised a dramatic new demonstration that made Earth's rotation visible to even a causal observer. Foucault realized that the plane of oscillation of a pendulum would slowly turn, or precess, as a result of Earth's rotation. He demonstrated this precession using large pendulums installed in Paris.
• The Berry College Foucault pendulum is a 16-meter (53-foot) long pendulum with a 107-kg (236-lb) bob that swings back and forth about once every 8 seconds. The pendulum's plane of oscillation precesses with a period of about 42 hours, thus demonstrating the rotation of the Earth.
• Use the links to the left to learn more about the history of the debate over Earth's rotation, understand how the Foucault Pendulum works, and try out the interactive simulations that let you explore the science yourself!