Lesson 2.4: A Closer Look at Forces and Newton’s Third Law

Suppose a vehicle hits a concrete barrier (or another immovable object) and comes to a sudden stop. If you are a passenger, you will tend to keep moving forward according to Newton’s first law of motion. Without safety restraints, your body will then collide with a part of the vehicle, which will by then be stationary. By taking a closer look at the forces on both your body and the vehicle part, you gain a better understanding of why you could sustain injuries. As some may know, being a passenger in a vehicle that is involved in a collision is a terrifying experience.

You have examined the dynamics of objects interacting mainly from the perspective of one of the involved objects. In this lesson you will widen your perspective to include the experience of the other object involved. You will take a closer look at the forces on both objects and the relationship between these forces as expressed in Newton’s third law of motion.

• Read pages 257 to 259 of the textbook. Answer the questions as you encounter them.
  

In the next activity, you will explore the forces and the changes in momentum of objects during an interaction.

 

• Read “2.4 Summary” on page 262 of the textbook. Then, complete “2.4 Questions” on pages 262 and 263.
  
  Check your answers with those in the “Practice Answers” in the online course.

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Go to Assignment 2.4: A Closer Look at Forces and Newton’s Third Law.