Chapter 7, Problem 27A

Consider the two forces acting on a person who stands still, namely, the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they comprise an action—reaction pair? Why or why not?

To determine

Whether two forces acting on the person equal and opposite to each other.

Whether they comprise of action-reaction pair.

Explanation of Solution

Introduction:

As per Newton’s third law of motion, there exists an equal but opposite reaction force for an action force.

When a person stands still on the floor, the net force on it is zero. The two forces- gravitational force pulling the person downwards and the upward normal force are equal and opposite in nature.

As the person is not directly in contact with the ground, there would exist two pairs of interaction forces. The weight of the person would act on the floor and the normal reaction force would act on the person from the floor. The floor would exert the force on the ground which would exert opposite yet equal force on the floor.

Conclusion:

Thus, as per Newton’s third law of motion, the two forces would be opposite yet equal in nature. There would be two pairs of interaction forces.