Rolling Friction

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Most of us have used cycles and some of us still do. You must have noticed that well filled tyres make cycling a whole lot easier than the tyres that are not completely filled with air. This is due to rolling friction between the tyres and the road.

When a body rolls over another body, the places of contact get deformed and a slight bump is formed.

The bump caused in front has to be constantly overcome. It is like constantly climbing an incline. Secondly, the adhesive forces between the two surfaces also have to be overcome constantly. It is due to these two factors that rolling friction arises. It is denoted by f_r and is given by

= coefficient of rolling friction

R = normal reaction

r = radius of rolling body

This equation is applicable only for pure rolling and no sliding. It also must be noted that the coefficient of rolling friction, m_r, has the dimensions of length.

Friction is a necessary evil

By now you must have realised that friction has more advantages than disadvantages. Let us see some advantages and disadvantages of friction.

Advantages

• Friction aids walking. Our feet pushes the floor back and the floor pushes our feet forward, by using friction to do so (every action has equal and opposite reaction).

• Friction between tyres of vehicles and the road make controlled motion possible.

• Many machine parts stay in place and are also driven by friction.

• All kinds of brakes in vehicles use friction for braking.

• Nails stay in place in the walls because of friction.

Disadvantages

• Friction causes wear and tear in machine parts.

• A large amount of fuel and energy in vehicles and machines is used to overcome friction.

• Friction between the bone joints, especially legs in old people, causes discomfort, pain and various ailments.