HOMEWORK Page: 115 Problems: all even

4.3 Newton’s Third law

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

THE NEWTON’S THIRD LAW

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

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

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

ACTION - REACTION pair = DO NOT cancel each other

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.)

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

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

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.

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.

Classwork Page: 117 Problems: Quick Check

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

HOMEWORK Page: 120 Problems: all

ANSWERS TO WORKSHEET EXAMPLES

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

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

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