What's the role of friction in vertical circular motion?

Friction in vertical circular motion prevents the object from slipping and maintains the circular path.

In more detail, friction plays a crucial role in vertical circular motion, which is a type of motion where an object moves in a circular path vertically. This is often observed in scenarios such as a roller coaster loop or a spinning bucket of water. The role of friction here is to provide the necessary centripetal force that keeps the object moving in a circular path.

Centripetal force is the force that makes an object follow a curved path, and its direction is always orthogonal to the velocity of the body, towards the fixed point of the instantaneous centre of curvature of the path. In the absence of friction, there would be nothing to provide this force, and the object would move in a straight line path, as per Newton's first law of motion.

In the case of a car moving in a circular path, for instance, the friction between the car's tyres and the road surface provides the centripetal force. If the road is icy or wet, reducing the friction, the car is more likely to skid or move off the circular path. Similarly, in the case of a roller coaster, the friction between the wheels of the coaster and the tracks provides the necessary centripetal force to keep the coaster moving in its vertical circular path.

Moreover, friction also prevents the object from slipping. When an object is in vertical circular motion, it experiences different forces at different points in its path. At the top of the circle, the object experiences the force of gravity pulling it down, and the tension or normal force pushing it up. At the bottom of the circle, these forces are reversed. If there were no friction, the object could slip at these points, especially at the top of the circle where the force of gravity is strongest.

Therefore, friction is essential in vertical circular motion as it provides the necessary centripetal force and prevents the object from slipping off its circular path.