Okay, these questions are relatively complex from my perspective. Bare with me if they turn out to be simple to the rest of you... Question one. This one will require that some assumptions be verifierified before the question will make sense. Premise 1: Energy possesses mass Premise 2: The velocity of a body is relative to the velocity of the observer. The same is true of acceleration Premise 3: Kinetic Energy, as a form of energy, has mass. (i have a feeling this is where my mistake lies) Okay, so question one. Is the mass of an object relative to the position of the observer? In other words, if a body is falling toward or away from an observer, the body would have a kinetic energy relative to the observer in proportion to the velocity of the body. As kinetic energy is a from of energy, and energy has mass, increased kinetic energy would have mass. Would this mean that the mass of an object is NOT a fixed quantity regardless of the location of the observer? This presents MASSIVE (LOL) problems, as that would indicate that the effect of gravity produced by the body would be relative to the vector of the observer. Question 2: As a body falls toward another body, and is accelerated by gravity, it's velocity is increased relative to the body toward which it falls. As we know that the mass of an object increases with it's velocity, this object becomes more massive as it accelerates. Would this object be "objectively" more massive? By that i mean, would an observer traveling the same vector observe this increase in mass, or would it be more massive only within a given point of reference? Okay, that's my first attempt to explain these ideas that i have in my head. I don't have the math to get it all out, and as i'm sure you all know, you can do a LOT more in your head than you can with words. Someone ask for clarification if my question doesn't make sense.