Section 4.8 Banking of a Curve
In order to protect vehicles on a curvy road to skid outward, the road is slanted towards its outer edge which is called the banking of a curve. As the speed of vehicle increases, the centripetal force needed for circular motion of the vehicle also increases. On the level road the frictional force between tire and the road provides the necessary centripetal force Subsubsection 3.3.2.1 but as the speed increases this friction is not sufficient enough to provide required centripetal force which results in skid the vehicle off the road in opposite direction of the curve. To avoid such calamity the road is banked so that tire has protection from skidding upward. Due to banking necessary centripetal force is provided by the components of frictional force and normal force. Since the frictional force acts on a running tire and road is static in nature (unless it skids), it is directed towards upper edge of the slanted road if the car is running with low velocity or at rest. However the frictional force acts towards lower edge of road if the car has high velocity because the car has tendency to skid towards upper edge of the road.
