A thin inelastic string is tightly wound on a cylinder. One of the ends of the string is attached to the above surface. Initially the whole system (string +cylinder) is held near the surface. When it is released from that position, find the acceleration of the centre of mass of the cylinder.
When we are calculating the sum of the forces on the body we are not taking into account the frictional force between the cylinder and the thread. Why is it so?