(a) What is Brownian motion? Draw a diagram to show the movement of a particle (like a pollen grain during Brownian motion.)(b) In a beam of sunlight entering a room, we can sometimes see dust particles moving in a haphazard way in the air. Why do these dust particles move?

(a) The zigzag movement of the small particles suspended in a liquid or a gas is called Brownian motion.

(b) When a beam of sunlight enters a room, suspended dust particles are seen moving haphazardly. This is because the dust particles are constantly hit by the fast-moving particles of air and due to this remain suspended despite gravity acting on them. This is an example of Brownian motion.