Article
Article
Brownian motion
Article By:
Barger, Vernon D. Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin.
Last reviewed:November 2021
DOI:https://doi.org/10.1036/1097-8542.097200
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The irregular motion of a body arising from the thermal motion of the molecules of the medium in which the body is immersed. A body that is immersed experiences many collisions with the molecules in the medium, which impart energy and momentum to the body. Because, however, there are fluctuations in the magnitude and direction of the average momentum transferred, the motion of the body appears irregular and erratic, as shown in the illustration. Brownian motion, also known as Brownian movement, was discovered by the Scottish botanist Robert Brown, who observed through a microscope that the very fine pollen grains of the plant Clarkia pulchella continuously move about when suspended in water. Brownian motion occurs in mixtures of different microscopic substances. See also: Classical mechanics; Collision (physics); Colloid; Energy; Molecule; Momentum; Motion; Physics; Statistical mechanics; Thermodynamic principles
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