Sorry for the delay.
As the water is not compressible, if it is pushed backwards, there would be some gap of *something* in the front of the plane. It's not a good analogy. May we continue with air ?
Fair enough but I simply used it to give a better insight.
This raises more questions:
If the air is pushed backwards during the plane's acceleration, there is more pressure in the back of the cabin than in the front It seems logical as air molecules are pushed backwards but can't allow empty space in the front. You said that they expand there, so the pressure lowers. Is it correct ?
Molecules get agitated by vibrations/sound and friction, right? When you run in a sports hall, you feel the friction of air on your body. If you try to swing a ping pong bat really fast, it puts pressure on your wrist due to the force.
You are compressing the air in front because of that speed of swing.
In a plane, your acceleration is doing the same thing inside the cockpit. like a bat compressing the air and you feel that on your body as a force whilst under acceleration only, but to feel it for a while, your plane must accelerate rapidly each second, because once it levels out, so does the air pressure.
If the air is pushed backwards, why the pilot's body isn't pushed too ? I can ask in another manner. What pushes the air back and why this *force* (or call it the name you want) doesn't push on the pilot ?
The pilots body is pushed, only he/she has a seat that absorbs that push, plus a large strong body frame that can easily dissipate that energy under normal flight conditions.Remember. Our bodies are designed to live under strong atmospheric forces and it takes huge accelerations to distress us in a closed environment.
Some planes do have open cockpits. There is no glass around the pilot, just outside air at atmospheric pressure. How can the air around him can be pushed backwards, as it will immediately equalize with the surrounding air? You still experience some accelerations in these planes.
The air around him is pushed backwards but marginally, because an open cockpit plane will not be going fast enough, so all he/she will feel, is deflected wind onto them.
When I'm in a plane accelerating before take-off, I cleary feel the seat pushing on my back, not the air around me pushing on my body. How do you explain that ?
No, you don't feel that seat pushing on your back. You feel your back pushing onto that seat. Your body frame is large and your head is small, so your body takes the lions share of that compression which results in you being pushed back.
Get in your car and tie a rubber ball on a string onto your sun visor. Now accelerate away and watch that ball come at your face. It's just compression of air.
If people try to look for the complicated gravity forces and what not, they will never grasp the simple concept.