Brownian Motion
Introduction
Brownian motion, also known as pedesis, is a phenomenon that involves the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the fast-moving molecules in the fluid. This motion is named after the botanist Robert Brown, who first observed the movement in 1827.
History
The concept of Brownian motion predates the kinetic theory of gases. The Roman poet Lucretius' scientific poem "On the Nature of Things" (c. 60 BC) has a description of Brownian motion of dust particles in verses 113–140 from Book II. He uses this as a proof of the existence of atoms.
The first person to describe the phenomenon in detail was the British botanist Robert Brown in 1827. Brown was studying pollen grains of the plant Clarkia pulchella suspended in water under a microscope when he observed minute particles, ejected by the pollen grains, executing a jittery motion. By repeating the experiment with particles of inorganic matter he was able to rule out that the motion was life-related, although its origin was yet to be explained.
Mathematical Model
The mathematical model of Brownian motion has several real-world applications. It is used in physics to calculate, among other things, the drift velocity of a fluid, the diffusion constant, and the mobility of particles. In mathematics, it is a fundamental example of a stochastic process, and is used to construct other, more complicated stochastic processes and stochastic differential equations.
Physical Properties
The physical properties of Brownian motion are characterized by a number of parameters. These include the diffusion coefficient, which is a measure of the speed at which particles move through a fluid, and the friction coefficient, which quantifies the resistance to motion of the particles.
Applications
Brownian motion has applications in many areas of science and engineering. For example, it is used in physics to model the behavior of particles in fluids, in chemistry to understand the process of diffusion, and in finance to model the behavior of stock prices.
See Also
