Brownian movement definition of Brownian movement in the Free Online Encyclopedia.

Brownian movement or motion, 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 colloid (kŏl`oid) [Gr.,=gluelike], a mixture in which one substance is divided into minute particles (called colloidal particles) and
..... Click the link for more information. )—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 kinetic-molecular theory of gases, physical theory that explains the behavior of gases on the basis of the following assumptions: (1) Any gas is composed of a very large number of very tiny particles called molecules; (2) The molecules are very far apart compared to
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Brownian movement

The irregular motion of a body arising from the thermal motion of the molecules of the material in which the body is immersed. Such a body will of course suffer many collisions with the molecules, which will impart energy and momentum to it. Because, however, there will be fluctuations in the magnitude and direction of the average momentum transferred, the motion of the body will appear irregular and erratic.

In principle, this motion exists for any foreign body suspended in gases, liquids, or solids. To observe it, one needs first of all a macroscopically visible body; however, the mass of the body cannot be too large. For a large mass, the velocity becomes small. See Kinetic theory of matter