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Foucault's Pendulum
Foucault's Pendulum
Resource Typeimage
TitleFoucault's Pendulum
Coverage / Year1939
DescriptionThe Foucault Pendulum hangs suspended via a sixty-four foot, six inch length of thin cable, has a sixteen-inch diameter brass sphere, filled with lead shot and weighs 650 pounds. Situated underneath the pendulum is a terrazzo platform inlayed with a compass rose, time scale and a circular degree scale. The length of time per swing is 8.9 seconds; the apparent movement of plane of swing is ten degrees per hour.
InterpretationIn 1851, Jean-Baptiste Foucault (1819-1868) suspended a sixty-two pound pendulum with 228 feet of piano wire from the dome of the Pantheon in Paris, France to demonstrate that the Earth rotates on its axis. The ball or 'bob' was held to one side by a string until it had come perfectly to rest. Then, the string was burned to start the pendulum swinging. This careful starting procedure was used to eliminate any extraneous forces, allowing only gravity to affect the weight, thus producing a pendulum swing in a true plane. A light stylus on the bob traced the path of the swing in a layer of fine sand on the floor. The apparent hourly deviation of a Foucault Pendulum depends on the latitude. The deviation is fifteen degrees at the poles, zero degrees at the equator, and ten degrees in Chicago. Once started, the pendulum's swing was fixed by its inertia in a constant plane in space. Since the pendulum was free to swing in any direction with respect to the building (and therefore the earth), Foucault knew that the Earth's rotation would cause an apparent movement of the plane of swing, which could be seen if the pendulum would swing long enough. The pendulum did swing for a long time. Although air resistance continually reduces the amplitude of a pendulum's swing, Foucault's heavy bob had sufficient speed to greatly reduce the effect of air resistance on each swing. The extremely long length of the wire made the period of the swing very slow, about 250 swings per hour. Time passed and those present could see by the marks in the sand that the pendulum did swing in a different direction with respect to the floor. Foucault's Pendulum experiment confirmed Nicolaus Copernicus' (1473-1543) theory that the Earth rotates on an axis. Copernicus theorized that the planets revolve around the Sun, in contrast to Claudius Ptolemy who theorized that the planets and Sun revolve around the Earth.
Lesson Plans / ThemesHow we learn about communities;
Learning Standards16 History; 10-12 Science; 13 Science, Technology and Society;
Author or CreatorFoucault, Jean-Baptiste, 1819-1868
SourceAbbott, David Ed. Physicists, The Biographical Dictionary of Scientists. New York: Peter Bedrick Books, 1984. Edward De Bono. Eureka! Illustrated History of Inventions From the Wheel to the Computer. New York: Holt, Rinehart & Winston, 1974
Subject / KeywordsPendulum; Mechanical tools; Equipment; Astronomy; Copernicus, Nicolaus, 1473-1543; A Century of Progress; World's Fair;
Collection PublisherMuseum of Science and Industry, Chicago;
Further InformationFor any further information related to this record, please contact the Collection Publisher. See for more information about this project.
Rights Management Statement
Resource Identifier39.179
CONTENTdm file name12532151982002_FAUCULTP.jpg
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