Question

1. which of the following is an example of a normal force?

the force of the ground pushing upward on a book
the force of gravity that pulls a book downward
the gravitational force that a book exerts on the earth
the friction between a book and the ground it rests on

Explanation:

A normal force is a contact force that acts perpendicular to the surface of contact. The force of the ground pushing upward on a book is a normal force as it is a contact force (between the book and the ground) and acts perpendicular to the surface (ground). The force of gravity pulling a book downward is gravitational force. The gravitational force a book exerts on the Earth is also gravitational (based on Newton's third law, but not a normal force). The friction between a book and the ground is a frictional force (parallel to the surface, not normal).

Answer:

the force of the ground pushing upward on a book