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Q.9 Give examples to show that friction is both a friend and a foe.
Answer :

Advantages of friction:
(i) We are able to walk because of friction.
(ii) Friction between the tip of the pen and a paper allows us to write.
Disadvantages of friction:
(i) Tyres and soles of shoes wear out because of friction.
(ii) Friction between the different parts of machines produces heat. This can damage the machines.