Teaching Newton's Third Law of Motion
Forces in Motion
If your students are preparing to study Newton's Third Law of Motion, then they should be familiar with the terms of motion as well as Newton's First Law of Motion and Newton's Second Law of Motion. Be sure that students understand forces in particular and how they apply to motion. Remind them that force is the product of mass and acceleration as stated in Newton's Second Law of Motion. Then, move on to the motion activity listed below. If students have difficulty grasping the concept of force as stated in Newton's Second Law of Motion, refer them to the Newton's Second Law of Motion Study Guide.
Activity to Illustrate
For this motion activity you will need a rod of some type, two balls of equal weight and two equal lengths of rope or string.
- Describe Newton's Third Law of Motion to students as for every action there is an opposite and equal reaction.
- Place the rod so that each side of the rod is balanced on a level surface and each level surface is of an equal height.
- Tie each ball to a string.
- Tie each string to the rod so that the balls hang at an equal distance from the floor and are side by side and touching.
- Ask a student to pick up one ball and drop it so that it swings against the other ball.
- Discuss the fact that the hit ball moved roughly the same amount of distance from the ground as the first ball was when it was dropped.
- Using Newton's Third Law of Motion, explain why the ball that was hit moved as well as why it moved where it did.
- Ask one student to place their hand on the side of one of the balls so that they are preventing it from moving. The side that the student is holding should not be touching the other ball.
- Pick up and drop the first ball as you did during the first part of this activity.
- Discuss what happens when the first ball drops and hits the second ball.
- Discuss how Newton's Third Law of Motion applies to this experiment.
When this activity is complete, discuss how Newton's Third Law of Motion impacts our everyday lives. For instance, why are airbags in cars necessary? How does Newton's Third Law of Motion apply to them?
Upon completion of this activity, students should understand and be able to use Newton's Third Law of Motion. Use the Newton's Third Law of Motion Study Guide to reinforce what students have learned or to assist them in understanding how it works.