Explain the reason behind:
(a) Use of parachutes while jumping from an aircraft during emergency.
(b) Floating of clouds in the sky.
(c) Settling of dust particles in a closed room.

Explanation

(a) Due to its huge structure, a parachute experiences a large viscous force. So, it descends the air with a very small velocity and helps in landing a person safely on ground or water.
(b) Clouds consist of tiny droplets of water. These droplets are so small that effect of gravity is negligible for them. Therefore, they do not come to earth and appear to be floating in the sky.
(c) Dust particles are spherical bodies of very small radii. So, after acquiring the terminal velocity, they start falling through the air with uniform speed. As terminal velocity of a body is directly proportional to the square of radius of the body, therefore, the terminal velocity for dust particles will be very small and they will settle down in a closed room after some time.