Brownian Motion

Brownian motion, also known as Brownian movement, any of several physical phenomena in which some amount is regularly experiencing small, random fluctuations. 


Whenever someone sprays a bottle of perfume across the room and some seconds later you start to smell the perfume in the air. Have you ever speculated how the perfume molecules traveled to the room you are in followed by your nose? Or have you observed how a drop of food color travels in a glass of water? Yes, it does spread out in seconds without even a mild stirring at all and eventually ends up color the whole glass of water. Both these phenomena occur due to the presence of Brownian Motion. 


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Brownian Movement

“Brownian motion denotes the random movement exhibited by tiny particles that are suspended in any fluids. This random movement is commonly known as Brownian Motion. This random motion of particles happens as a result of particle collisions that are fast-moving and immersed in water. 


The name of Brownian motion is derived from the Scottish botanist Robert Brown, who noticed pollen grains moving erratically in water. He defined the motion in 1827 but was unable to explicate it. While pedesis derives its name from Brown, he was not the first personality to explain it. It was a Roman poet Lucretius who described the motion of dust particles around the year of 60 B.C., which was further utilized by him to present as evidence of atoms. 


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The phenomena of transportation remained a mystery until 1905 when Albert Einstein published a paper that explained the pollen was being moved by the water molecules in the liquid. As with Lucretius, Einstein's explanation served as indirect evidence of the existence of atoms and molecules. At the beginning of the 20th century, the being of such tiny components of matter was only a theory. In 1908, Jean Perrin experimentally verified Einstein's hypothesis, which earned Perrin the 1926 Nobel Prize in Physics "for his work on the discontinuous structure of matter."


The mathematical explanation of Brownian motion is a comparatively easy probability calculation, of significance not just in the subjects of physics and chemistry, but also to describe other statistical phenomena. The first person to propose a mathematical model for Brownian motion was Thorvald N. Thiele in a paper on the least-squares method that was published in 1880. A contemporary model is the Wiener process, named in honor of Norbert Wiener, who described the function of a continuous-time stochastic process. Brownian motion is a well-thought-out Gaussian process and a Markov process with continuous path occurring over continuous time.


What is Brownian Motion

If some particles are subjected to Brownian motion, they are present in a given medium and there is no preferred direction for the random oscillations, then over a period of time, the particles will incline to blowout homogeneously all over the medium. Thus, if A and B are two regions lying adjacent to each other than at time t, A contains twice as many particles as B, at that instant the probability of a particle’s leaving A to go in B is double as great as the likelihood that a particle will leave B to go in A. 


Causes and Effects of Brownian Motion

Brownian motion describes randomness and chaos. It is one of the simplest models of randomness. The various causes and effects of this motion are listed in this subsection.


  1. What causes Brownian Motion?

The size of the particles is inversely proportional to the speed of the motion, i.e. Small particles exhibit faster movements.

This is because the transfer of momentum is inversely proportional to the mass of the particles. Lighter particles obtain greater speeds from collisions.

The speed of the Brownian motion and viscosity of the fluid are inversely proportional. The lesser the viscosity of the fluid, the quicker is the Brownian movement.

Viscosity is a quantity that expresses the magnitude of the internal friction in a liquid. It is the measure of the fluid’s resistance to flow.


  1. Effects of Brownian Motion

Brownian movement causes a constant motion in the particles in a fluid. 

This prevents particles from settling down, leading to the stability of colloidal solutions.

A true solution can be distinguished from a colloid with the help of this motion.

Albert Einstein’s paper on Brownian motion was vital evidence on the existence of atoms and molecules. The kinetic theory of gases which explains the pressure, temperature, and volume of gases is based on the Brownian motion model of particles. 


Brownian Motion Examples

Maximum instances of Brownian motion are transportation processes that are affected by greater currents, yet also exhibit pedesis.

Examples comprise:

The movement of pollen grains on still water.

Motion of dust motes in a room (though largely influenced by air currents).

Dispersal of pollutants in the air.

Dispersal of calcium over bones.

Motion of "holes" of electrical charge in semiconductors.


Significance of Brownian Motion

The initial significance of defining and unfolding Brownian motion was that it reinforced the modern atomic theory.

FAQ (Frequently Asked Questions)

1. What Causes Brownian Movement in a Colloidal Solution.

Colloidal “solutions” consist of minute particles (solid or liquid) which cannot be seen by the naked eye but can be seen through a microscope, suspended in a liquid medium (solvent). They are not true solutions. For example, milk. Milk consists of minute fat particles suspended in water. The fat particles scatter light and can be seen. Now the question is why milk appears to be “milky”? (opaque and white) and not like water? So, you can observe Brownian motion when the fat particles are kicked here and there by the water molecules.

2. What is the Difference Between Brownian Motion and Motility?

It can be quite complex to differentiate between a movement due to Brownian motion and movement due to other effects. In biology, for example, an observer needs to be able to tell whether a specimen is moving because it is motile (capable of movement on its own, perhaps due to cilia or flagella) or because it is subject to Brownian motion. Typically, it's imaginable to segregate the processes because Brownian motion appears jerky, random, or like a vibration. True motility appears often as a path, or else the motion is twisting or turning in a specific direction. In microbiology, motility can be established if a culture inoculated in a semisolid medium wanders away from a stab line.