Action/Reaction Pairs of Forces
As we have already discussed, any interaction is made up of an action force and a reaction force. Note: Any time one object is exerting a force on a second object, the second object must exert a force back on the first object, and this pair of forces make up the action force and the reaction force in a SINGLE interaction.
In the cartoon at the right, if we say that the action force is the force exerted by the snowball on the kid, then the reaction force must be the force exerted by the kid on the snowball. The two forces together make up a single interaction.
Please note: The action force involves the same two objects as the reaction force. The two objects just play opposite roles in the action force and in the reaction force; if in the action, the first object exerts a force on the second object, then in the reaction, the second object will exert a force on the first.
Now, it's your turn. In the self-quiz below, see if you can identify the reaction force and its direction given the action force and its direction.
Identifying Action and Reaction Pairs of Forces Self-Quiz
Scroll to the top of the page and read the material if you have not already. When you are ready to complete the exercise, fill in all the blanks. Then, press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!