Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Pushing a box up a hill

A person is pushing a box up a hill. What force is related by Newton's third law to the person's force on the box?

The box's force on the person. Incorrect answer: The person's force on the box is opposed by friction, and also by gravity.

This answer fails all three parts of the POFOSTITO test, the most obvious of which is that three forces are referred to instead of a pair.

→ Solved problem: More about example 2 page 176, problem 20

→ Solved problem: Why did it accelerate? page 176, problem 18

Last Update: 2009-06-21