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One of the longest-running exhibits at Science Park is the Foucault Pendulum, which was purchased in 1957 and has hung in the tower of the Museum of Science ever since. Although the signage and viewing window have been updated over the years, the pendulum itself has never been altered. The large brass bob rotates gently back and forth throughout the day, knocking into small pins set in a circle around the perimeter to mark the passage of time.
Scientists have used pendulums since the 16th century to measure and understand time, mass, and gravity. A basic pendulum is made of a weight suspended on a string, but complex variations of pendulums have been developed with different technical elements to study different aspects of gravity and mass.
French physicist Leon Foucault developed his model of pendulum in 1851 to demonstrate the rotation of the Earth. Although a simple device, it provided critical evidence about the Earth's movement.
The Museum of Science purchased this pendulum model from the California Academy of Science, who produced and sold several pendulums during the second half of the 20th century. Similar models were installed at the United Nations in New York and the Smithsonian Institute in Washington, D.C. The pendulums designed by the Cal Academy are now produced by Academy Pendulums, who have more detailed information on their website: https://www.academypendulums.com/article.html.
Technical drawings from the California Academy's pendulum handbook.
The large brass bob of the MOS's pendulum hangs at the bottom of a nearly 70-foot steel cable which is suspended up into the Museum tower, guided by a sensing mechanism, control electronics, and an electromagnetic ring to maintain its swing. The sensor at the top monitors the movement of the cable and briefly turns on the electromagnetic ring, near the suspension point, to control the cable and maintain a regular, even swing throughout the day. The long cable, along with the weight of the brass bob (235 pounds!) keep the Pendulum swinging smoothly. The glass enclosure also helps keep the Pendulum free from the effects of air currents.
Beneath the revolving pendulum is an enormous stone mosaic commissioned by the Museum in the early 1960s. This art piece, modeled after an Aztec calendar stone by sculptor P. David Holleman, was installed alongside the pendulum in 1962 as another approach to studying time and change. The colorful stones and details provide a bright backdrop for the pegs to be knocked down hourly by the swinging brass bob.
Want to learn more?
Want to learn more?
This site uses simple drawings to explain the function and design of Foucault's pendulums.
Smithsonian Institute
Smithsonian Institute
Although no longer on display, the Smithsonian had a similar pendulum in their National Museum of American History and provide a good explanation of its mechanics on this site.
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