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Brownian motion
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Two-panel diagram illustrating Brownian motion. The top shows a Brownian particle among randomly moving blue molecules, while the bottom highlights uneven molecular collisions on the particle's surface, causing its movement.
Diagram illustrating Brownian motion, showing red and brown circles representing particles above and below a blue wavy line, with many small gray dots symbolizing atoms.
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Brownian motion summary
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Italian-born physicist Dr. Enrico Fermi draws a diagram at a blackboard with mathematical equations. circa 1950.
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Two-panel diagram illustrating Brownian motion. The top shows a Brownian particle among randomly moving blue molecules, while the bottom highlights uneven molecular collisions on the particle's surface, causing its movement.
Brownian particle (Left) Random motion of a Brownian particle and (right) random discrepancy between the molecular pressures on different surfaces of the particle that cause motion.

Brownian motion

physics
Also known as: Brownian movement
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Brownian motion, any of various physical phenomena in which some quantity is constantly undergoing small, random fluctuations. It was named for the Scottish botanist Robert Brown, the first to study such fluctuations (1827). If a number of particles subject to Brownian motion are present in a given medium and there is no preferred direction for the random oscillations, then over a period of time the particles will tend to be spread evenly throughout the medium....

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