What is Brownian motion?

Brownian motion refers to the random motion of suspended particles in a liquid or gaseous fluid due to the unpredictable collision between particles and solvent molecules caused by thermal fluctuations. 

Brownian motion is often demonstrated through the movements of small particles such as pollen that can be observed in the liquid under the sunlight. An important feature of Brownian motion is that small particles move fast while large particles move slowly. Therefore, the diffusion behaviors of particles can be used to calculate the particle size.

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