# Newton’s third law of motionPage 1

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Slide 1 Forces and Interactions

Newton’s Third Law of Motion

Summary of Newton’s Laws

Vectors

Slide 2 ## Forces and Interactions

Interaction

is between one thing and another.

requires a pair of forces acting on two objects.

Example: interaction of hand and wall pushing on each other

Force pair—you push on wall; wall pushes on you.

Slide 3 ## Newton’s Third Law of Motion

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

Slide 4 A soccer player kicks a ball with 1500 N of force. The ball exerts a reaction force against the player’s foot of

A. somewhat less than 1500 N.

1500 N.

somewhat more than 1500 N.

None of the above.

Newton’s Third Law of Motion

Slide 5 A soccer player kicks a ball with 1500 N of force. The ball exerts a reaction force against the player’s foot of

A. somewhat less than 1500 N.

1500 N.

somewhat more than 1500 N.

None of the above.

Newton’s Third Law of Motion

Slide 6 Newton’s Third Law of Motion

Action and reaction forces

one force is called the action force; the other force is called the reaction force.

are co-pairs of a single interaction.

neither force exists without the other.

are equal in strength and opposite in direction.

always act on different objects.

Slide 7 Newton’s Third Law of Motion

Reexpression of Newton’s third law: To every action there is always an opposed equal reaction.

Example: Tires of car push back against the road while the road pushes the tires forward.

Slide 8 Newton’s Third Law of Motion

Simple rule to identify action and reaction

Identify the interaction—one thing interacts with another

Action: Object A exerts a force on object B.

Reaction: Object B exerts a force on object A.

Example: Action—rocket (object A) exerts force on gas (object B).

Reaction—gas (object B) exerts force on rocket (object A).

Slide 9 When you step off a curb, Earth pulls you downward. The reaction to this force is

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