CyberJIT,
Our observation of light movement is NOT distorted at all, regardless of our relative speeds. If we're moving towards an incoming beam, or away from it, or parellel to it, we still measure it to have the same relative velocity because our perception of time is altered by our speed. This is not intuitive I know, but it has been backed up by experiments with jets flying at different speeds around the Earth (a few seconds were lost/gained in one case, so you could theoretically increase your life span by living on a jet, ignoring the effect it would have on your health).
Acceleration due to gravity is 9.8 ms^-2 but only on Earth. It is less on Mars and more on Jupiter. There is an element of deception in giving this acceleration an exact value. What if an object more massive than Earth was being attracted towards us due to gravity? What will happen, is that both Earth and the more massive object (x), will move towards a centre of gravity. Object x will still accelerate towards the centre of gravity at 9.8 ms^-2, however Earth will be accelerating towads this point even faster, and their relative acceleration will be the sum of these two accelerations (in different directions obviously).
I'm fairly sure the effects of gravity are propogated at the speed of light, but I'm not entirely sure. I think this is still being tested in experiments.
You raise an interesting point about objects moving away from each other. What if one object is going one direction at 60% of the speed of light, and another object is going in the opposite direction at 60% of the speed of light. Their relative velocity is (in Newtonian physics) 120% of the speed of light. I'm honestly not sure whether this is allowed in general relativity. Surely it would have to be. Perhaps someone can answer this question.
Kashi
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