Brownian motion

American  

[brou-nee-uhn moh-shuhn] / ˈbraʊ ni ən ˈmoʊ ʃən /

noun

Physics.

1. the irregular motion of small particles suspended in a liquid or a gas, caused by the bombardment of the particles by molecules of the medium: first observed by Scottish botanist Robert Brown in 1827.

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Brownian motion Scientific  

/ brou′nē-ən /

1. The random movement of microscopic particles suspended in a liquid or gas, caused by collisions between these particles and the molecules of the liquid or gas. This movement is named for its identifier, Scottish botanist Robert Brown (1773–1858).

2. See also kinetic theory

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Brownian motion Cultural  

1. The erratic motion, visible through a microscope, of small grains suspended in a fluid. The motion results from collisions between the grains and atoms or molecules in the fluid.

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Discover More

Brownian motion was first explained by the twentieth-century physicist Albert Einstein, who considered it direct proof of the existence of atoms.

Etymology

Origin of Brownian motion

1870–75; Brown + -ian

Example Sentences

Moving from large-scale systems to molecular machines introduces challenges such as Brownian motion, which makes precise control more difficult.

From Science Daily • Mar. 31, 2026

Though debate continued for decades, the correct answer came from botanist Robert Brown, for whom Brownian motion was named.

From Seattle Times • Jul. 21, 2023

It was Albert Einstein who, starting in his epochal year of 1905, published several papers that explained precisely how Brownian motion could be used to measure the size of atoms and molecules.

From Textbooks • Aug. 12, 2015

In 1905, Einstein demonstrated that the quantum explained the photoelectric effect and the strange phenomenon known as Brownian motion.

From New York Times • Feb. 16, 2015

Clumps and clusters of birds in flight were questing back and forth, black dots against the blue sky, moving in some kind of desperate Brownian motion.

From "American Gods" by Neil Gaiman