Why does a spring stretch when rotated in uniform circular motion?
The horizontal rod containing the massless spring(stiffness = k) and block of mass 'm' is rotated uniformly about point P.
This centripetal force is provided by the elastic(restoring) force of the stretched spring which is 'kx' where x is elongation of the spring as compared to rest position.
Everything looks very neat very decent.
I am listing the problem as seen from two reference frames.
1. Rotating frame (as seen from rod).
As seen from the rod, centrifugal force is acting outwards. This will cause the block to move towards right, and hence stretching the spring. The centrifugal force will be balanced by the spring force acting left. Everything seems fine.
2. Inertial Frame (ground)
I am unable to understand why does the spring stretch in the first place? There is no reason why the spring should stretch. Their is no force acting on the block in the outward direction. There is a centripetal force acting on the block when it is undergoing rotation. But that force is towards the center. So the spring should contract???