Give examples to show that friction is both a friend and a foe.
Advantages of friction:
(1) We are able to walk because of friction.
(2) Friction between the tip of the pen and a paper allows us to write.
Disadvantages of friction:
(1) Tyres and soles of shoes wear out because of friction.
(2) Friction between the different parts of machines produces heat. This can damage the machines.