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Brownian Movement

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The random or zig-zag motion of a particle in a colloidal solution or in a fluid is called Brownian motion or Brownian movement. This motion was first discovered by a botanist Robert Brown in 1827 while observing the movement of pollen grains in the water with a microscope, hence, the name Brownian motion or Brownian movement. The physics behind the Brownian movement and its theoretical model was first published by Albert Einstein in 1905.

Let’s learn about Brownian Movement its properties, and others in detail in this article.

What is Brownian Movement?

Brownian Motion occurs in a colloidal solution or in a fluid when the particle of the colloidal solution collide with each other randomly. Brownian movement is observed in liquids as well as in gases. For example, when sunlight enters a room, we may sometimes observe microscopic dust particles suspended in the air moving quickly and randomly. This is an example where Brownian motion in gases (as air is a gas) is demonstrated. 

Since they are constantly impacted by fast-moving air particles, the small dust particles move around. Though we cannot see the incredibly small particles or molecules of air, we can witness the effect created by their continuous and quick motions. The quick and random movement of small dust particles hanging in the air demonstrates that air is made up of particles that are continuously moving. Brownian motion is the zig-zag random movement of tiny particles floating in a liquid or gas. Brownian motion leads to two conclusions regarding the nature of matter,

  • The matter is made up of small particles 
  • Particles are in a state of continuous motion.

Brownian motion is the uncontrolled or irregular movement of particles in a fluid caused by collisions with other fast-moving molecules. Random particle movement is usually reported to be stronger in smaller particles, less viscous liquids, and at higher temperatures.

The following image shows the Brownian movement of the particle inside a gas chamber,

Brownian Movement of particles in a gas chamber.


Brownian Movement in Colloids

Brownian motion is best described in colloidal solutions. This motion is observed in colloidal solutions because the particles collide with unequal forces because the particle size is not uniform in the colloidal solution. The particles in the colloidal solution do not coagulate and settle at the bottom of the container because of the Brownian Movement.

Cause of Brownian Motion

The different causes of the Brownian Motion can be summarized as follows,

  • The velocity of the particles is inversely proportional to the square root of the mass of the particles, therefore the smaller size particles move faster as compared to the larger size particles and vice versa. Therefore, after the Brownian motion smaller particles quickly acquire a higher velocity.
  • Viscosity of fluids (a resistive force) is inversely proportional to the speed in Brownian Motion, i.e., a higher viscosity restricts the motion of the particle, whereas a lower viscosity results in a higher velocity. Therefore, Brownian motion is more dominant in the lower-viscosity fluids.
  • Velocity of the particles is directly proportional to the temperature of the fluid and therefore higher the temperature higher will be the Brownian motion and vice versa.

Effects of Brownian Motion

Various effects of the Brownian Motion are,

  • Particles of fluid (liquid or gas) are in constant motion because of the Brownian movement.
  • Brownian motion is responsible for distinguishing a true sol from a colloidal sol.
  • Brownian motion prevents the coagulation of some solutions.

Brownian Motion Examples

The random or zig-zag motion of the particles in a fluid (liquid or gas) is Brownian motion. The following daily-life examples show the presence of Brownian motion in natural phenomena,

Movement of Dust Particles in Room

The dust particles being tiny in size are not visible to the naked human eye, however, the movement of dust particles is visible to the human eye due to the Tyndall effect (scattering of the light). 

Diffusion of Particles in the Air

Air pollutants, dust particles, gas molecules, and dust motes are mixed up in the air and exhibit the Brownian motion. There are several types of pollutant gases (carbon dioxide, carbon monoxide, sulfur, etc.) in the air that mix up with the air and deteriorates its quality due to Brownian motion.

The particles in the air get diffused and follow the Brownian Motion.

Diffusion of Particles in the Air


Movement of Electrons in Conductors

Conduction of electricity is only possible with the movement of electrons inside a conductor, however, due to the presence of a large number of free electrons in the conductor, their motion is followed by the Brownian motion when there is no electric field applied.

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FAQs on Brownian Motion

Q1: What is the Brownian movement?


The random or zig-zag motion of particles in a fluid (liqiuid or gas) is called the Brownian movement.

Q2: What is the cause of the Brownian movement?


The particle in the colloidal solution collides with each other with unequal forces which cause these particles to move randomly in a zig-zag motion this motion is called as Brownian Motion.

Q3: What are examples of Brownian motion?


Various examples where Brownian motion can easily be seen are,

  • Motion of pollen grains on the surface of the water.
  • Motion of dust particles in the atmosphere.

Q4: How does the Brownian motion affect temperature?


As the energy of the particle of the solution increases with the increase in temperature the Brownian motion of the colloidal solution increases.

Q5: What is the Brownian Movement in Chemistry?


In Chemistry Brownian movement is also called Brownian motion, is defined as the random movement of particles of the fluids because of their collision with other fluid molecules.

Generally, the movement of a particle is easily observed in the less viscous liquid, with smaller-sized particles, and at a higher temperature.

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Last Updated : 18 Apr, 2023
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