As long as the discussion has become ------- --consider the "vomit comet".
How do you measure the kinetic energies of the people floating inside and bumping into each other .
-I am just a country boy - but to me a craft floating/flying in a moving sea of air, is in exactly the same situation as the people floating in the airplane.
gravity is still working of course but the any forces are only relative to the interior of the cabin - nothing else.
No?