Question 3: When you stand still on the ground, how large a force does the earth exert on you? Why doesn’t this force make you rise up into the air?
Force exerted by earth on us
When someone stands still on the ground, s/he exerts a force equal to his/her weight on the earth VERTICALLY down. (By definition, your weight is the force with which the earth’s gravity pull you). The earth pushes you NORMALLY up with the same force. This is called Normal force or normal reaction of the earth. This normal force enables us standing on the earth and also realizing our weight. If it did not exist we would have sunk in the earth like we sink in water!
This the force exerted by the earth when we stand still on its surface is equal to our weights.
Why we do not rise up in the air?
Now, both these forces are equal and opposite. Therefore, there is no net force acting on the person. The zero net force means we are not pushed in any direction, of course including the upwards. So, the reason we do not rise up in the air.