In rough surfaces there are holes and cracks which contain air in them.When a body slides on rough surface,air in the holes is pushed out to create vaccum and holds the body and don't let it to slide..Hence ,rough surfaces increase friction.
3 ways where increase friction is used are:
1.In vehicles,tyres are retreated to increase the friction.
2.Mountaineers use hooked shoes to increase the frriction.
3.Feet of the horses are fitted with horse shoes to increase the friction.
3 ways wherein decrease friction is used are:
1.Skating ranks are made plain and smooth to decrease the friction.
2.iceskates are made smooth and plain for easy skating.
3.Ball bearings are oiled to decrease the friction in machines.
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