Foucault pendulum
A Foucault pendulum is an educational device that illustrates the Earth's rotation through its swinging motion. Developed by French physicist Léon Foucault, the first pendulum was demonstrated at the Paris Observatory in 1851 and later showcased a larger version at the Pantheon in Paris. This demonstration was significant as it provided tangible proof of the Earth's axial rotation, a concept that was not widely accepted at the time despite advancements in astronomical understanding. The pendulum swings in a fixed plane while the Earth rotates beneath it, leading to the observable gradual shift in the pendulum's bob position, completing a full rotation in about 33 hours at the latitude of Paris.
The Foucault pendulum became a pivotal moment in science communication, making complex scientific ideas accessible to the general public and solidifying Foucault's reputation as a leading scientist. Its impact reached beyond science, as it inspired future demonstrations and became a staple in museums and educational institutions worldwide. Today, it continues to serve as a teaching tool, illustrating fundamental principles of physics and Earth science, while also featuring in popular culture, notably in Umberto Eco's acclaimed novel, "Foucault's Pendulum."
Foucault pendulum
A Foucault pendulum is a device designed to demonstrate the rotation of Earth. Named for Léon Foucault, a French physicist who built the first such device, the Foucault pendulum made its debut at the Paris Observatory in February of 1851. Several weeks after his initial demonstration, Foucault created a larger pendulum, consisting of a 62-pound bob that was suspended from the roof of the Pantheon in Paris with a 220-foot wire. This exhibition attracted a great deal of attention in both scientific and lay circles.
At the time of Foucault's public exhibition, scientists had amassed a growing body of evidence supporting the theory that Earth was not stationary but in fact moved through space. However, it was not yet widely accepted that Earth also rotated on its axis as it circled around the sun, and the Foucault pendulum is regarded as the first time that hard proof of Earth's axial rotation connected with a mass audience in an easily understandable form.
Background
Léon Foucault was born in Paris in 1819, and he demonstrated an aptitude for the construction of machines during his childhood and teen years. After a brief stint as a medical student, Foucault began conducting photography tests using microscope lenses. With a rising reputation as a scientist, Foucault went on to collaborate with fellow French physicist Hippolyte Fizeau on a series of groundbreaking experiments intended to measure the speed of light. His 1851 invention of the Foucault pendulum is considered the first major scientific breakthrough of his career.
For centuries, thinkers and scientists had speculated about the rotational movement of the Earth. Aristarchus of Samos was one of the first theorists to propose Earth's orbit and axial rotation as explanations for the apparent movement of stars across the night sky. However, influential early astronomers and mathematicians including Hipparchus of Nicaea and Claudius Ptolemy rejected Aristarchus's theory. In its place, they supported the idea that Earth occupied a central place in the cosmos, with everything revolving around it. This idea prevailed until it was challenged by scientists including Nicolaus Copernicus, Giordano Bruno, and Galileo Galilei. Although the revolutionary work of these European astronomers was initially controversial, their findings were later adopted by the scientific mainstream.
As astronomical study and inquiry continued, scientists found mounting evidence that long-held traditional views about space and the universe were highly erroneous. By Foucault's time, scientific understanding of space had greatly advanced, expanding to include concepts such as solar systems, galaxies, and the possible existence of exotic objects such as black holes. It was also universally accepted that Earth was a spherical object, suspended in space, and revolved around the sun. However, theories that Earth also rotated on its own axis during its orbit had not yet been conclusively proven in a way that was accessible to laypeople.
The Foucault pendulum provided that elusive proof. Foucault's giant display at the Pantheon in Paris showed that the position of the pendulum's swinging bob changed at a rate of about 11.25 degrees per hour, completing a full rotation in slightly less than 33 hours. Earth's rotation was the only explanation that could account for the changing position of the bob, while the northern latitude of Paris explained why it took 33 hours, rather than 24 hours, to make a complete rotation. Thus, the Foucault pendulum proved not only that Earth was spinning on its axis but also established the rate at which it was rotating. When corrected to account for latitude, a Foucault pendulum would complete a full rotation in 23 hours, 56 minutes, 4.1 seconds. This length of time is known as a sidereal day, and marks the amount of time it takes for Earth to fully rotate on its axis.
Impact
Foucault's exhibition at the Pantheon caused a sensation with international reach. The gradual rotation of the Foucault pendulum was repeated in demonstrations given to large crowds in cities across Europe and North America, and Foucault's reputation as one of the leading physicists of his time was cemented. On a popular level, the Foucault pendulum marked the point at which it became widely accepted that Earth rotated on its axis as it circled around the sun. From a scientific standpoint, the invention marked a breakthrough in scientific understanding of orbital mechanics.
In 1852, the year after his initial demonstration, Foucault used a gyroscope to demonstrate the rotation of Earth in an even simpler and more accessible way. In his gyroscope experiment, Foucault used the device's circulating rotor to demonstrate constant motion relative to the position of Earth, but not to that of the stars. Foucault's gyroscope consistently reverted to its initial position after one full day, regardless of the latitude at which the experiment was conducted. Because its results were not dependent on latitude, some science historians consider Foucault's gyroscope demonstration to be even more successful than his pendulum exhibition.
Foucault went on to earn the prestigious Copley Medal from the Royal Society of London in recognition of his achievements, and he was appointed to a position at the Imperial Observatory in Paris in 1855. While there, Foucault pioneered several important improvements in telescope technology, including the use of concave mirrors to achieve greater degrees of magnification. In 1862, Foucault became the first modern scientist to measure the speed of light accurately, using a revolving mirror to determine that light travels at a rate of 299,796 kilometers per second. Using the currently accepted speed of light as a benchmark, Foucault's initial calculation was 99.999 percent accurate.
Although Foucault's original pendulum was a highly simplistic invention from a technical and mechanical standpoint, it functioned with such ease and clarity that it has gone on to become a common feature at scientific museums and universities around the world. In the twenty-first century, it is still used to demonstrate the principle of Earth's axial rotation to students. Foucault's pendulum was also immortalized in popular culture when it became the namesake of a widely read 1988 novel by the Italian author and philosopher Umberto Eco.
Bibliography
Aczel, Amir D. Pendulum: Leon Foucault and the Triumph of Science. State University of New York Press, 2007.
Beech, Martin. The Pendulum Paradigm: Variations on a Theme and the Measure of Heaven and Earth. Universal Publishers, 2014.
Berman, Bob. Zoom: From Atoms and Galaxies to Blizzards and Bees: How Everything Moves. Hachette UK, 2014.
"Foucault Pendulum." Department of Earth and Environmental Sciences, University of Munich, www.geophysik.uni-muenchen.de/outreach/foucault-pendulum. Accessed 17 Nov. 2016.
"The Foucault Pendulum." School of Physics, University of New South Wales, www.animations.physics.unsw.edu.au/jw/foucault‗pendulum.html. Accessed 17 Nov. 2016.
"Foucault's Pendulum." Franklin Institute, www.fi.edu/foucaults-pendulum. Accessed 17 Nov. 2016.
Giacometti, Jose A. "Foucault Pendulum Revisited, the Determination of Precession Angular Velocity Using Cartesian Coordinates." Revista Brasileira de Ensino de Fiscia, vol. 43, 2021, doi.org/10.1590/1806-9126-RBEF-2019-0140. Accessed 3 Jan. 2022.
Mann, Adam. "What's Up with That: How a Swinging Pendulum Proves the Earth Rotates." Wired, 27 May 2014, www.wired.com/2014/05/wuwt-foucaults-pendulum/. Accessed 17 Nov. 2016.
Sparkes, Matthew. "What Is Foucault's Pendulum?" Telegraph, 18 Sept. 2013, www.telegraph.co.uk/technology/google/google-doodle/10317223/What-is-Foucaults-Pendulum.html. Accessed 17 Nov. 2016.