UPSC CSE Prelims 2003

Correct Option

When a vehicle moves at high speed along a sharp circular path, two primary effects can occur:

• Skidding outwards (Statement 3): A centripetal force is required to maintain the circular trajectory. This force is primarily provided by the friction between the tires and the road. If the vehicle's speed is excessively high or the turn is too sharp, the required centripetal force may exceed the maximum static frictional force available. Consequently, the vehicle loses traction and skids outwards, away from the center of the circular path. This phenomenon is often understood in the non-inertial frame of the vehicle as the effect of an outward-acting centrifugal force.
• Overturning about its outer wheels (Statement 1): During a turn, the centrifugal force acts horizontally outwards through the vehicle's center of gravity. This force generates a torque that tends to lift the inner wheels. If this overturning torque becomes sufficiently large to overcome the restoring torque due to the vehicle's weight, the vehicle will overturn. This overturning typically occurs around the line connecting the points of contact of the outer wheels with the ground, causing the inner wheels to lift first.

Therefore, statements 1 and 3 are correct.

Incorrect Options

• Overturning about its inner wheels (Statement 2): Overturning occurs when the outward centrifugal force creates a torque that lifts the inner wheels. The pivot point for overturning is the outer edge of the vehicle, specifically the outer wheels. Therefore, overturning happens about the outer wheels, not the inner ones.
• Skidding inwards (Statement 4): Skidding inwards implies the vehicle moves towards the center of the circular path. This is contrary to the effect of centrifugal force, which always pushes the vehicle outwards from the center of the turn when the required centripetal force is not met.