In your discussion of the force concept you may have heard that a force is a push or pull exerted by one object on another. You may also have heard a popular expression of Newton’s third law: “For every action, there is an equal, but opposite reaction.” Unfortunately, this expression leads to some naïve conceptions about forces. Unlike Newton’s first two laws, which deal with the effects of forces on a single object, the third law describes the interaction between two objects. In this experiment, you will examine this interaction in a variety of situations so that you might develop a better understanding of the forces involved when two objects interact.


In this experiment, you will

  • Observe the magnitude and direction of forces exerted by interacting objects.
  • Observe the time variation of these forces.
  • Develop a more robust expression of Newton’s third law.