What's the difference between i.e. and e.g.?
straight line having one end fixed to a body and the other end attached to a moving point and used to describe the position of the point relative to the body. As the point moves, the position vector will change in length or in direction or in both length and direction. If drawn to some scale, the change in length will signify a change in the magnitude of the vector, while a change in direction will signify a rotation of the vector. Changes in magnitude and direction are the only changes that a position vector can experience, and the velocity of the point is defined as the time rate of change of the position vector.