Hello, my textbook says that the magnitude of centripetal acceleration is equal to the sum of the forces acting on that object. (this is in regard to an object in a circular path, by a string. See https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Centripetal_force_diagram.svg/220px-Centripetal_force_diagram.svg.png for an example) I was wondering why is this so? To me, it doesn't make sense that they are equal in magnitude, since the forces are perpendicular. Please help.