freefall adn uniform motion in space feel the same because as you accelerate towards earth you eventually stop accelerating this called terminal velocity, and is because the byouyancy of the atmosphere and the gravitaion accleration acting on your body cancel out.
In free fall you are not accelerating. As you approach terminal velocity, the drag/resistance/friction of the upwardly accelerating atmosphere begins to accelerate you upward.
At terminal velocity you are being accelerated upward at 9.8m/s/s. You can check this with an accelerometer.
And where/why are you introducing buoyancy?
If we assume that the FlatEarth is accelerating and we put a person outside it, 1 of two things would happen
1) the person might be in tandem with the flatearth , in which case they woudl feel thelelves accelerating (because of the UA), because there is no atmosphere to cancel it out
or
2) they would see the Flatearth acclerating away from them, because they are not accelerating ( in this case you have to explain why the UA is not affecting them).
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