Browian motion

Brownian motion is the constant random (or haphazard) movement of tiny particles in fluids.

Experiment to demonstrate Brownian motion

Experiment 1: Using Pollen grains.

When pollen grains molecules are dropped in water or suspended in water and observed through a microscope,

The molecules will be seen making irregular movements in random directions.

This shows that particles of matter are ever in a state of constant random motion.

Experiment 2: Using Smoke particles in air.

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Smoke is placed in a glass cell and the glass cell illuminated with light from one side.

The smoke particles are then observed from above using a microscope.

Observation:

White specks of smoke particles will be seen moving in a constant random motion.

This shows that particles of matter are ever in a state of constant random motion.

Explanation:

The constant random motion is due to un even collision (or bombardment) of the invisible air molecules with the visible pollen grains or smoke particles.

Factors that affect Brownian motion

(i) Temperature

When the temperature of the smoke cell is increased, smoke particles are seen moving faster and when it is reduced, they are seen moving slowly.

Increase in temperature increases the kinetic energy of the molecules, hence they move faster than before.

Decrease in temperature decreases the kinetic energy of the molecules, hence they move slowly.

ii) Size and density of the particles

When the size of the particles is increased, Brownian motion is reduced and when the size of particles is reduced, Brownian motion increases.