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Brownian movement

Brownian movement, zigzag, irregular motion exhibited by minute particles of matter when suspended in a fluid. The effect has been observed in all types of colloidal suspensions (see colloid)—solid-in-liquid, liquid-in-liquid, gas-in-liquid, solid-in-gas, and liquid-in-gas. It is named for the botanist Robert Brown who observed (1827) the movement of plant spores floating in water. The effect, being independent of all external factors, is ascribed to the thermal motion of the molecules of the fluid. These molecules are in constant irregular motion with a velocity proportional to the square root of the temperature. Small particles of matter suspended in the fluid are buffeted about by the molecules of the fluid. Brownian motion is observed for particles about 0.001 mm in diameter; these are small enough to share in the thermal motion, yet large enough to be seen with a microscope or ultramicroscope. The first satisfactory theoretical treatment of Brownian motion was made by Albert Einstein in 1905. Jean Perrin made a quantitative experimental study of the dependence of Brownian motion on temperature and particle size that provided verification for Einstein's mathematical formulation. Perrin's work is regarded as one of the most direct verifications of the kinetic-molecular theory of gases.

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Brownian movement

Brownian movement The continuous random movement of microscopic solid particles (of about 1 micrometre in diameter) when suspended in a fluid medium. First observed by Robert Brown in 1827 when studying pollen grains in water, it was originally thought to be the manifestation of some vital force. It was later recognized to be a consequence of bombardment of the particles by the continually moving molecules of the liquid. The smaller the particles the more extensive is the motion. It can be observed in the particles of a colloidal solution and in the cytoplasm and nucleoplasm of dead cells.

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Brownian movement

Brownian movement Random, zigzag movement of particles suspended in a fluid (liquid or gas). It is caused by the unequal bombardment of larger particles, from different sides, by the smaller molecules of the fluid. The movement is named after the Scottish botanist Robert Brown (1773–1858), who in 1827 observed the movement of plant spores floating in water.

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Brownian motion

Brown·i·an mo·tion / ˈbrounēən/ • n. Physics the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium.

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Brownian motion

Brownian motion The random movement of small particles which are dispersed in a colloidal solution or suspension. See BROWN, ROBERT.

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Brownian motion

Brownian motion Random movement of small particles dispersed in a colloidal solution or suspension.

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