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How To Observe Brownian Motion Under the Microscope

How To Observe Brownian Motion Under the Microscope

Brownian motion is the random movement of particles in a fluid or gas caused by collisions with other particles in the medium. The phenomenon is named after the botanist Robert Brown, who observed the erratic movement of pollen grains in water in 1827. Brownian motion occurs on a molecular level, and it is a fundamental concept in physics and chemistry.

In Brownian motion, the particles move in a zigzag pattern, constantly changing direction due to the impacts of the surrounding fluid or gas molecules. The speed and direction of each particle are unpredictable, and over time, the particles become evenly distributed throughout the medium.

Brownian motion has many practical applications, including the modelling of the diffusion of gases, liquids, and solids, and the movement of microscopic particles in biological systems. It is also used in financial mathematics to model stock price movements, and in computer simulations of complex systems.

Why smoke particles?

In this video, Paul uses smoke particles which provide a simple and effective way to visualise the random movement of small particles in a fluid or gas. Because smoke particles are relatively large and easy to see, they can demonstrate Brownian motion without requiring specialised equipment. Additionally, observing Brownian motion with smoke particles can help illustrate the concept of diffusion and the random nature of molecular motion, which has applications in various fields, including physics, chemistry, and biology.

You will need:

  • Microscope: A 4/10 objective will work
  • A “Whitely Bay” smoke cell – essential that the smoke pot is really clean (a pipe cleaner will work).
  • Round cover slip for the pot.
  • 12v Power Pack
  • Leads
  • Paper straw
  • Matches / lighter
  • Heatproof mat for the straw /match


  1. Light the top of the straw.
  2. Keep it upright and let burn until smoke flows from the bottom of the straw.
  3. Place above the pot until it is full of smoke.
  4. Slide cover slip across to trap as much of the smoke sample as possible
  5. Adjust the focus and lighting as needed to get a clear image.

It’s important to note that the method for viewing Brownian motion under a microscope may vary depending on the type of microscope and the technique used.

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