1. HOMEWORK
Page: 115
Problems: all even

2. 4.3 Newton’s Third law

3. Learn about The Newton’s Third Law Identify action-reaction pairs
TODAY’s OBJECTIVES
Learn about The Newton’s Third Law
Identify action-reaction pairs
Identify friction

4. THE NEWTON’S THIRD LAW

5. Forces always exist in pairs
The basis for the Newton’s Third Law

6. For every ACTION, there is an equal and opposite REACTION
THE NEWTON’S THIRD LAW
If two objects interact, the magnitude of the force exerted on object 1 by object 2 is equal to the magnitude of the force simultaneously exerted on object 2 by object 1, and these two forces are opposite in direction
For every ACTION, there is an equal and opposite REACTION

7. ACTION - REACTION pair = forces that objects exert on each other
THE NEWTON’S THIRD LAW
ACTION - REACTION pair = forces that objects exert on each other

8. ACTION - REACTION pair = DO NOT cancel each other

9. THINK ABOUT IT… (on a worksheet)
A child causes a wagon to accelerate by pulling it with a horizontal force. Newton’s third law says that the wagon exerts an equal and opposite force on the child. How can the wagon accelerate? (Hint: Draw a free – body diagram for each object.)

10. THINK ABOUT IT… (on a worksheet)
A child causes a wagon to accelerate by pulling it with a horizontal force. Newton’s third law says that the wagon exerts an equal and opposite force on the child. How can the wagon accelerate? (Hint: Draw a free – body diagram for each object.)
The reaction force (from the wagon) acts on the child, not on the wagon itself, so there is still a net force on the wagon

11. Example 3 (on a worksheet)
identify the action-reaction pairs in the following situations: a. A person takes a step. b. A snowball hits someone in the back. c. A baseball player catches a ball. d. A gust of wind strikes a window

12. Example 4 (on a worksheet)
If a small sports car collides head-on with a massive truck, which vehicle experiences the greater impact force? Which vehicle experiences the greater acceleration? Explain your answers.

13. Example 4 (on a worksheet)
If a small sports car collides head-on with a massive truck, which vehicle experiences the greater impact force? Which vehicle experiences the greater acceleration? Explain your answers.
Each impact force has the
same magnitude (3rd Law). The sports car experiences the larger acceleration because it has a smaller mass, and acceleration is inversely proportional to mass.

14. Classwork
Page: 117
Problems: Quick Check

15. Classwork Page: 118 - 119 Problems: Investigation 4-3
Part 1 and Part 3

16. HOMEWORK
Page: 120
Problems: all

17. ANSWERS TO WORKSHEET EXAMPLES

18. Practice Problems
Page: 112
Problems: 3 (Nathan)
4 (Lauryn)

19. Practice Problems Page: 115 Problems: 2 (Larissa) 4 (Jack)
6 (Volunteer)

20. Practice Problems Page: 120 Problems: 2 (Larissa) 4 (Jack)
6 (Volunteer)