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

Friction is both a friend and a foe due to following reasons:
Friction act as friend:
• We are able to walk because of frictional forces between ground and our feet.
• We are able to write because of friction between ball point and the paper surface.
• Nails and screws stick to wall surfaces because of friction.
• Lighting a match stick is because of friction between match stick and the side surface of match box.
Friction act as foe:
• Wear and tear of soles of our shoes is due to friction.
• When a tyre deflates, it is difficult to move the vehicle because of increased friction between the tyre and road surface.
• Machines gets heated up because of friction.
• Due to friction, machines and vehicles consumes more fuel and increase maintenance cost.

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