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When I jump off of something, even with eyes closed I can be pretty certain that I'm falling due to the associated sensation of falling. However, as gravity should be affecting each of my internal organs equally, surely the sensation must be due only to the air resistance, which causes my outer body to accelerate slower than my organs?

As a follow up, assuming the above is correct, would the best way to minimise the sensation of falling be to keep as narrow a profile as possible I.e. keep pencil shape rather than spread arms and legs out flat?

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  • $\begingroup$ Are you comparing the sensation of falling to the sensation of being weightless? $\endgroup$
    – DanDan面
    Commented May 6, 2023 at 21:37
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    $\begingroup$ A large contribution to your "associated sensation of falling" is the lack of reaction force applied to your body by the earth. Minimizing your profile won't make that part of the sensation disappear. $\endgroup$
    – Amit
    Commented May 6, 2023 at 21:46

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When you're in an elevator, you can easily feel when it's accelerating up or down. But that can't be due to air resistance: the elevator carries its air with it, so you feel no air resistance.

What happens is that the stresses on your body change. If the acceleration is downward, you have less force keeping your various parts and the elevator moving together. In a freely falling elevator, that force is ~zero, and that's the same as freely falling without the elevator.

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As a rule, air resistance can be neglected while the mass of air displaced is much smaller than the mass of the moving object. Since you have about 1000 times the density of air, you can neglect air resistance in your dynamics while you are moving much less than 1000 body lengths. This same logic applies to falling sheets of paper, which behave differently than falling reams of paper, and also helps explain why aerodynamic forces are important in golf and baseball but not really in basketball.

Unless you skydive, free fall is a good approximation for your dynamics. (A homework problem is how long it takes a skydiver to reach their terminal velocity; I remember six or ten seconds.) In free fall, the fluid in the vestibular system of your inner ear does not accumulate in the bottoms of its little channels. This is different from the situation when you are standing or lying down. It is the difference that you associate with the sensation of falling.

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