Question

Can normal force do work? If not, why not? If so, give an example.

Answer 1

Hint: Usually normal force does not perform any work, since the action of normal work does not produce any motion. But there are some cases where the direction of motion is parallel to the direction of the normal force. In these cases work is said to be done by the normal force.

Complete answer:
If a force acts across a distance, it performs work, otherwise, it does not. It is said that normal force cannot alter the speed of an object moving along a surface. Normal force, acting as centripetal force, can change an object's motion, but no work is done since acceleration is perpendicular to velocity.

Normal force is not used to complete any tasks. A block going up or down an incline does not operate with normal force. Because the normal force is, by definition, perpendicular to the surface, and the block slides along the surface, no component of the normal force is parallel to the motion.

In some cases normal forces do perform work. Consider the following example: A person is travelling in an elevator. The normal force is the force imposed on the individual by the elevator floor. As the elevator ascends, so does the individual. Meaning the normal force is parallel to the motion of the person conducting work. The normal force and negative work are anti-parallel to the motion of the elevator as it descends.

Note: Normal force is a contact force. A normal force cannot be exerted on two surfaces that are not in touch. For example, if the surfaces of a table and a box are not in touch, they cannot exert normal forces on each other. When two surfaces, such as a box and a table, come into contact, they exert a normal force on each other that is perpendicular to the contacting surfaces. This normal force will be as strong as is required to keep the surfaces from piercing each other.