Originally Posted By: redewenur
When you change posture from sitting to standing, various parts of your body are in motion relative to each other. That is to say, each of those parts exists within its own F of R.


Yea but more relevently you're accelerating. If you stand up without accelerating (assuming no relative motion of body parts), then you wouldn't perceive yourself as moving, rather you'd feel the room was moving around you.

I think that very clear explanation of time and space vectors implied the thing's being viewed from some arbitrary reference frame, not necessarily its own.