I’ve gone skydiving before, and you have maybe 1-2 seconds of that small drop in your stomach feeling before you reach terminal velocity at about 120mph. But that should only make sense if the plane you are jumping out of is going about 90 mph in the vertical direction right? I’m assuming it’s not, maybe flying 90mph in the horizontal axis. So can someone explain why there’s still not a huge change in acceleration to cause that drop in stomach feeling?
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The “freefall feeling” only occurs when nothing is pushing on you. When exiting an airplane, the relative wind is pushing on you, first from the front and then gradually more below, so while you do feel a bit lighter at first, you don’t get to feel weightless. For that, you need to jump from a balloon, helicopter or stationary object, or go on a rollercoaster designed to have air-time (wooden rollercoasters usually have lots of this).
When you exit a plane at 90mph, you will begin accelerating downward at 9.81m/s^2 – but you will also begin accelerating backward at about half that rate, because of the aerodynamic drag on your body. You are losing horizontal velocity as you are gaining vertical velocity in fact, your total acceleration is larger than it would be if the plane was stationary.
But the G force that you feel is a function of the aerodynamic force acting on you, which depends on your speed. You don’t feel the gravitational force because it acts on every part of your body equally – that’s why, if you jump from a static object like a helicopter or hot air balloon, then for the first few seconds you would feel completely weightless, until you gain enough speed to generate significant air resistance.
When you are at terminal velocity, the air resistance is equal to your weight, so it presses up on your body with the same force you would feel if you were lying flat on the ground, so you feel 1G. But when you leave a plane travelling 90mph, the aerodynamic force on your body is about half that, so you’d feel about 0.5G – but you feel it horizontally rather than vertically.
Before you jump out of the plane, the plane is pushing up on you. When you jump, that force goes away suddenly. That’s an acceleration (at least, if you don’t want Einstein to describe General and Special relativity to you), which you feel. The plane isn’t pushing up on your feet, so your body isn’t pushing up on your stomach, so you feel your stomach move upwards(relative to you).
Then you also jump out into air travelling at 50 knots/miles per hour, or 25m/sec. You will start to decelerate in the horizontal direction as you are moving through the air in that direction but there is nothing to keep pushing you, but that force is at right angles to what your stomach is doing, so if anything it will add to the general weirdness you feel.
Then, as others have said, you start to speed up and the moving air is now pushing up on you, so now you are in a pretty normal 1G situation, with the moving air is pushing you up instead of the ground, so you feel pretty normal – except for your brain freaking out about all that nothing beneath you.
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