Question

Explain the need for banking of tracks.

Answer 1

In a leveled circular road, skidding mainly depends on the coefficient of static friction py. The coefficient of static friction depends on the nature of the surface which has a maximum limiting value. To avoid this problem, usually, the outer edge of the road is slightly raised compared to the inner edge. This is called banking of roads or tracks. This introduces an inclination, and the angle is called the banking angle. “Let the surface of the road make angle 9 with a horizontal surface. Then the normal force makes the same angle 9 with the vertical. When the car takes a turn.

Free body diagram of a particle including the centrifugal force 

there are two forces acting on the car:

(a) Gravitational force mg (downwards)

(b) Normal force N (perpendicular to the surface)

We can resolve the normal force into two components N cos θ and N sin θ. The component balances the downward gravitational force ‘mg’ and the component will provide the necessary centripetal acceleration. By using Newton's second law.

Effects of centrifugal force

The banking angle 0 and radius of curvature of the road or track determine the safe speed of the car at the turning. If the speed of the car exceeds this safe speed, then it starts to skid outward but frictional force comes into effect and provides an additional centripetal force to prevent the outward skidding.

At the same time, if the speed of the car is a little lesser than safe speed, it starts to skid inward and frictional force comes into effect, which reduces the centripetal force to prevent inward skidding. However, if the speed of the vehicle is sufficiently greater than the correct speed, then frictional force cannot stop the car from skidding.