Chapter 4, Problem 14Q

To determine

How large a force does the ground exert on us when we stand still on the ground? Why doesn’t this force make us rise up into the air?

Answer to Problem 14Q

Solution:

The magnitude of the force will be equal to our weight when we stand on the ground. We exert a force on the ground and the ground also exerts same force according to Newton’s third law. That is why the force is balanced and we do not rise in the air.

Explanation of Solution

According to Newton’s third law, for every action, there is an equal and opposite reaction. We exert a force on the ground when we stand on the ground is our weight and the ground exert the same magnitude of force in opposite direction.

The force exerted by the ground on us is:

$F=mg$,where m is your mass, g is acceleration due to gravity.

The downward force of our weight is balanced by an equal and opposite force exerted by the ground. The net force on our body is zero, our rate of acceleration is zero, and that is why the force is balanced and we don’t rise in the air.