I was reading about a situation in my brother’s physics textbook where a bike is riding along a curved vertical surface. It’s mentioned there that normal reaction provides the centripetal force and the bike does not fall off the wall because gravity is balanced by the friction between the bike and the surface ( if the speed is high enough). And friction depends on the normal reaction.
So my question is, what is creating the normal reaction here? My first guess was centrifugal force. But as far as I know, centrifugal force is not a real force and we need to take it into account only if our frame of reference is the bike itself. if FOR is the bike, then the bike can not have any acceleration and can be explained by centrifugal force balancing the normal reaction. But if the frame is stationary, there’s no centrifugal force. Then what’s creating a normal reaction here?