Foucault’s Pendulum






Leon Foucault was a French physicist born in Paris on September 18, 1819. After an education received chiefly at home, he studied medicine, which he abandoned in favor of physics. He is well known for his invention of the Foucault pendulum, which proved that the earth is not stationary, but revolves on its axis.

In 1851, Leon Foucault gave his first demonstration on the rotation of the Earth with the help of a long and heavy pendulum suspended from the roof of the Pantheon in Paris. The Earth’s rotation causes the trajectory of the pendulum to change over time, knocking down pins at different positions as time elapses. The experiment caused a sensation in both the learned and popular worlds, and “Foucault pendulums” were suspended in major cities across Europe and America.

In 1855, Foucault was awarded the Copley Medal of the Royal Society for his remarkable contribution and research. Foucault also won Napoleon III as a patron, who created a job for him at the Imperial Observatory. There he worked on telescopes and more precise experiments until his death in 1868.

Among his other scientific achievements, Foucault upended Isaac Newton’s theory of the speed of light by proving that light moved more slowly through water than air; discovered electrical eddy currents; made an improvement to the mirrors used in reflecting telescopes; and conducted many experiments with gyroscopes which were important to the development of airplanes, telescopes, and spacecraft.

Google is commemorating Foucault’s 194th birthday with an animated doodle that depicts Foucault’s Pendulum in the Pantheon, Paris. Google’s doodle includes a rendering of the Foucault Pendulum swinging, along with a small clock and globe icon that, when clicked, allow users to control the pendulum’s movements.

Learn more:

How Léon Foucault taught us to watch the world spin

How Foucault’s pendulum proves that the earth is rotating

List of Foucault pendulum locations (see if there’s one near you!)

Foucault Pendulum on YouTube

The gyroscope was another tool used by Foucault to study the earth’s rotation

Leon Foucault’s biography

Foucault Pendulum Lesson Plan

(NOTE: in the above lesson plan, the list of pendulum locations isn’t complete; refer to the more accurate Wikipedia list instead.)

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