Give examples to show that friction is both a friend and a foe.

Friction as a friend :

1. We are able to walk on floor due to friction between floor and our feet.
2. We are able to write due to friction between pen and paper.
3. An object in motion will never stop if there is no friction.
4. Without friction between tyres of automobiles and roads, they could not be started, stopped or turned to change direction of motion.
5. Friction helps us to tie a knot.

Friction as a foe :

1. It wears out the materials like screws, ball bearing or soles of shoes.
2. Friction produces heat and so the jar of mixer becomes hot when it runs for a few minutes.
3. Friction slows down moving objects, hence, more force is required.
4. Due to friction blades of scissors or knives become blunt.
5. Due to increased friction between tire and the road surface, when the tire deflates, it becomes difficult to move the vehicle.