[Physics] Why can’t we feel acceleration under free fall?

equivalence-principlefree fallnewtonian-gravitynewtonian-mechanics

It's a common experience when we are in some vehicle like a car being accelerated we can feel the "invisible push/pull" or acceleration caused due to the change in velocity I assume we can always trust this ability of ours to decide if we are being accelerated whether in car/bus/train/rocket whenever our velocity changes we can feel it. In physics lectures you often hear professors saying that when a body say a closed box is freely falling (ff) say towards the earth, the man (or whatever) inside can never tell if he is in ff or somewhere in quiet space away from all matter with no gravity around.

But now you can see the problem in former the man's velocity is increasing by $9.8~\mathrm{m/s}$ every second now if I give a super-car and you put on the accelerator definitely your friend sitting besides, even if blind and deaf can tell if he is indeed accelerating or not. So now here is my question why the man inside the ff box can't feel the acceleration and (his velocity is changing wildly) and how is his state identical to that of a man standing still in deep space with no gravitational pull around.

I was seeking a intuitive answer which doesn't involve relativity theory as I don't understand it yet and which could be explained by classical mechanics.

Best Answer

CASE -I:Consider the acceleration of a body with mass M when a force of 100 N is applied on a body.
CASE-II : Consider the acceleration of the same body when a force of 1000 N and 900 N respectively are applied on it simultaneously in opposite directions.

The acceleration in both cases will be the same as the net force is 100 N.

Now consider the internal changes in the body. The body in case II is experiencing a much severe crushing power than in case I.

Similarly in a free fall only a single force is acting on the body. In all other cases cited in the question two or more forces are acting on the body in opposing directions.