A body needs a force F₁, just to start motion on a surface, a force F₂, to continue its motion and a force F₃ to roll on the surface. What is (i) the static friction (ii) sliding friction and (iii) rolling friction? State whether F₂, is equal, less than or greater than (a) F₁ and (b) F₃.

Friction is a necessity and also acts as an evil. Explain.

For successful launch of a rocket such as Chandrayaan from earth's surface to space, it has to overcome :

1. electrostatic force of earth.
2. gravitational force of earth.
3. frictional force of earth's atmosphere
4. both (2) and (3)

When you apply mustard oil to your hands, out of the following objects, which object will be difficult for you to hold :

1. Earthen cup
2. Thermocol tumbler
3. Wooden cup
4. Glass tumbler