When friction helps
So far we have discussed the harmful side of friction and the remedies for it. But there are occasions when friction is useful to us — and on some of them nothing would work without it.
Walking
We can walk over a surface only because that surface creates a frictional force on the soles of our feet and prevents them slipping. On wet ground, or ground where something like oil has been spilt, we are liable to slip and fall because the friction is low.
Tyres
Treads are cut into the tyres of a motor car to increase the friction between the surface of the wheel and the road. If there is not enough friction the car can skid and an accident can happen. In muddy or sandy places the wheels sometimes spin on the spot, and that too is because there is not enough friction for the wheel to move forward.
Figure to be added
Why treads matter in the rain
When vehicles run on wet roads, a layer of water between the tyre and the road reduces the friction between the two surfaces and the vehicle tends to skid. The treads are cut so that the water underneath the tyre has somewhere to escape to, which minimises the vehicle sliding on the water.
Rope
A rope is made by twisting coir fibres together. Even when a large force is applied to the rope its fibres do not come apart, and the reason is the friction between them.
Coir and nylon
A knot tied in a nylon rope comes loose more easily than one tied in a coir rope. That is because the frictional force acting between the coir fibres is greater than the frictional force acting between the nylon fibres.