Question

We feel our weight whenever we stand over any surface but we feel weightlessness when we jump from certain height.
Explain this statement by using Newton's 3rd law.
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Answer 1

What you feel as 'weight' isn't exactly the gravity, but the force which acts on your body to counter the gravity. When you're standing on the ground, gravity acts on each and every particle in your body depending on the mass of that particle (hence it is a body force). However, the reactionary force from the ground acts only below your feet (hence it is a surface force). This reactionary force then gets transmitted throughout your body in the form of compressive and shear stress, which gives you the feeling of weight. During freefall, there is only gravity acting on your body, but nothing to provide the reactionary force to counter it, and hence you feel weightless.

On a side note, when you are inside a rocket accelerating upwards, the reactionary force on your body is much larger than the gravity, which results in much stronger compressive and shear stresses on the individual organs of your body. This results in the feeling of extremely large weight.

Answer 2

AS WE KNOW THAT NEWTON S THIRD LAW OF MOTION STATES THAT ACTION IS EQUAL TO REACTION N THUS WGEN WE STAND ON THE GROUND THAN THE GROUND ALSO APPIES THE SAME FORCE BACK WHILE JUMPING WE R NOT IN CONTACT WITH GROUND SO THERE IS NO FORCE ACTING ON US