What i am going to write is an extremely basic question. It's not a paradox. But why I thought of writing it here, is because meny people go wrong in answering it. Let's see how many of you go wrong here. OK, the question is as simple as this :- You are in space surrounded by an isotropic medium of mass such that there is no gravity acting on you and on the small piece of stone you are holding. Somehow, you had, when you were young, borrowed a massless string from the Alpha Centaurians and you have that string in your pocket right now. So you take the string out, tie the mass to one of its ends, hold the other end and rotate it. The scene is this :- the stone is rotating about your hand with a constant speed of 'u'. The entire string is lying in the plane traced by the circular trajectory of the stone. Basically, it's a normal uniform circular motion. List down the forces acting on the stone. If you got an answer at this stage, of course, you are wrong because the question is still ambiguous. The forces will depend on the reference frame from which you are looking at it. So I need to specify the reference frame. OK, it's the frame from which you look stationary. Now list the forces.