There are 2 objects. Object 1 is stationary and Object 2 is in motion. Object 1's position in the 3D world is (x=0,y=0,z=0). I have Object 2's velocity (also in x,y,z directions). I need to calculate the speed at which Object 2 is moving towards (or away from) Object 1. Keep in mind that this will not be Object 2's speed, because it is not moving directly towards Object 1. It is moving on it's own path, but I need to know the change in speed towards Object 1. Hope I explained that good enough, if not then ask. How can this be done?