Can you say MOTION?

[ostren]

I maintain that all physical motion is relative.
False. "Motion" is not a precise term... I would avoid using it if I were you.
So.. let me think :grumpy: the word "motion" is no good; it isn't found in any treatise about Relativity or in any Physics text -- 'that right, chroot??

[russ_watters]

All motion is relative, but not absolutely relative (I'm sure you'll get a kick out of that). All motion is measured relative to something else, but you can't just pick anything you want and change frames at any time you want. What you need to accept is that assuming an arbitrary gravity field gets switched on (materializes from nothing) at the instant a rocket fires its motor is not a reasonable thing to do. edit: thinking about it more, you'd need two gravity fields materializing out of nothing - one to counter the acceleration of the rocket that fired its motor and another that varies its strength/distance continually to provide constant acceleration for its companion flying in formation with it.

Same goes for the car turning that somehow manages to make the earth accelerate with a small force.

In any case, I doubt warren will be real happy with a continuation of that convoluted discussion.