Normal forces won't exceed the weight (active force) on an object.

A ball is dropped from a height h. It bounces (vertically) on a tabletop, and raises back to a height just less than h. Which of the following best describes the normal force that the table exerts on the ball? Explain your choice.

a. The table cannot exert a force.

b. The normal force is less than mg.

c. The normal force is equal to mg.

d. The normal force is greater than mg.

 Correct Answer

Students suffering from this misconception will tend to choose answer c. A large number of the examples in physics texts and most classes deal with instances in which the normal force is equal to the weight. This can sometimes become a rote memory item that students apply to all situations.

Related misconceptions/student difficulties that may arise in the question:

Passive forces don't exist (tables don't exert a normal force).