when cycle is going on curved path why the normal reaction at top and bottom places is zero?

Hi

when the cycle is going on the curved path and is at the top then at this point of time 3 forces are acting at this body

1) weight - downwards (mg)

2) normal reaction - downwards

3) centrifugal force - outwards (mv^2r)

as we know normal reaction is self adjsuting force, at this point weight is counter balanced by the centrifugal force. so normal reaction is zero as mv^2r = mg.

But this is not the case at the bottom because centrifugal force and the weight are in the same direction, normal reaction will have to be there to conter balance the sum of these two. mg+mv^2r = N.