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Brownian Motion


The Brownian movement was first described in 1828 by the botanist Robert Brown, while investigating the pollen of several plants. For more than half a century following, a score of scientists studied this motion, common to organic and inorganic particles of microscopic size when suspended in a liquid, to determine the causes and dynamics of the motion.
Brownian Motion

What is Brownian Motion?

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Brownian motion is described as a random motion present in the case of gas or liquid (fluid), which results in the collision of the molecule present in the substance. In other words, we can say that Brownian motion is a zig zag motion of molecules.

Standard Brownian motion: It is a continuous time stochastic process. Another name of this motion is Wiener process.

Brownian Motion Equation

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Mathematical expression of Brownian motion is mentioned below:
D = $\frac{RT}{N_{A}6\pi \eta a}$

D = $\frac{k_{B}T}{6\pi \eta a}$
is the gas constant,
NA is the Avogadro number,
T is the temperature,
$\eta$ is the viscosity,
a is the radius of the brownian particle

What causes Brownian Motion?

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The main causes of Brownian motion is listed below:
  • The dispersed molecules are collide with dispersion medium continuously
  • Due to this collision, molecules moves randomly
  • Since it is a random motion, it is not in a straight line motion

So, this motion is the result of unequal bombardment of dispersed molecules and medium.
 Cause of Brownian Motion

Brownian Motion and Diffusion

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Brownian motion is the random movement of particles in a medium. In that movement the concentration of particles and velocity are different. Whereas, in the case of diffusion, the molecule will move from higher concentration to lower concentration region until the concentration become equal. Both motions are different in all respect.

Brownian Motion Examples

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The examples of Brownian motion are illustrated below:
  • Motion of a particle in a gas
  • Movement of an ant
  • Particles inside a collider