When vehicles go through turnings, they travel along a nearly circular arc. There must be some force which will produce the required acceleration. If the vehicles go in a horizontal circular path, this resultant force is also horizontal. Consider the situation in which a car of weight mg is moving on a horizontal circular road of radius r with a constant velocity v.
The external forces acting on the car are
The tyres have a tendency to slip outwards. Hence, the frictional forces act towards the centre. Thus, for a safe turn we must have
However, there is a limit to the magnitude of the frictional force. If ms is the coefficient of friction between the tyres and the road, the magnitude of friction cannot exceed msN. We know that
N = mg
Hence, if a car takes a turn at a velocity greater than v, then it will skid outwards.
