Hi everybody I have been trying to develop an intuitive general understanding of how the trajectory of an object , that is moving at constant velocity, is changed by the sudden appearance of a central force but I am not sure my reasoning is correct. (1) Consider an object "A" not subject to any force and, therefore, moving at constant velocity "V". (2) Now, suppose that, "by magic", a central force appears at a distance R from "A" constantly pointing to a point "O" in space. As far as I understand the path that A will take depends from its velocity "V" at the time the central force appeared: (a) If V=0, then A will start to oscillate around O (b) if V= SQR(a x R) (where: SQR = square root, "a" = the acceleration, constant in magnitude, to which A is subject) then A will start to move along a circular path (c) if V < SQR(a x R), then A will start moving along an elliptical path (the smaller V the more "sqeezed" the ellipse -- the case V=0 could be considered as the degenarate case of this) (d) if V > SQR(a x R), then the trajectory of A will be curved by the central force but the path will not be (necessarily ?) a "closed" one like a circle or an ellipse Is the reasoning above correct? Points (a), (b), (c) make sense to me, so I believe they are correct, but I do have strong doubts about point d ... Thanks a lot for your help!