'All laws of physics hold good in all inertial frames of reference.' observer A - standing still on earth observer B - in jetplane-1 flying at mach-2 jetplane-2 is moving at mach-1 co-directional to jetplane-1. A observes in accordance with Newton's 3rd law. B observes, fuel level going down in jet-2, exhaust moving out from the tail. But jetplane-1 is moving backwards for him, which is not in accordance with 3rd law. Again I know I am missing something here. Any clue what it is? thanks.