Newton's third law can be summarized as "every action has an equal and opposite reaction". In this problem, consider the action of the entire Earth on a person standing at rest on the ground and the opposite reaction, where ‘action’ and ‘reaction’ are understood to mean ‘force’ and ‘reaction force’ What is the "equal and opposite" reaction force to the gravitational force of the Earth acting on the person?

Action force: Would be the force of your feet against the Earth given by the weight defined as:

Where g is a constat who represent the gravity in Earth

Reaction force: Would be the force of the Earth pushing against your feet. And on this case is represented by the normal force defined as:

Where represent the friction coefficient between the ground and the object.

And the friction force.

If we don't have any other forces involved in the y axis we can conclude that:

And as we can see we have that Action force = Reaction force

So then the third Law of Newton is satisfied.

Explanation:

For this case we have this:

Action force: Would be the force of your feet against the Earth given by the weight defined as:

Where g is a constat who represent the gravity in Earth

Reaction force: Would be the force of the Earth pushing against your feet. And on this case is represented by the normal force defined as:

Where represent the friction coefficient between the ground and the object.

And the friction force.

If we don't have any other forces involved in the y axis we can conclude that:

And as we can see we have that Action force = Reaction force

So then the third Law of Newton is satisfied.

this is poiselle's equation from fluid mechanic in physics. mech eng