Lesson 4 | Newton’s Third Law - Hazleton Area High School

Lesson 4 | Newton¡¯s Third Law

Student Labs and Activities

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Content Vocabulary

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Lesson Outline

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MiniLab

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Content Practice A

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Content Practice B

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Math Skills

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School to Home

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Key Concept Builders

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Enrichment

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Challenge

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Lab A

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Lab B

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Lab C

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Chapter Key Concepts Builder

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Launch Lab

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Launch Lab

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LESSON 4: 10 minutes

How do opposite forces compare?

If you think about forces you encounter every day, you might notice forces that occur in

pairs. For example, if you drop a rubber ball, the falling ball pushes against the floor. The

ball bounces because the floor pushes with an opposite force against the ball. How do these

opposite forces compare?

Procedure

1. Read and complete a lab safety form.

2. Stand so that you face your lab partner,

about half a meter away. Each of you

should hold a spring scale.

3. Hook the two scales together, and

gently pull them away from each other.

Notice the force reading on each scale.

4. Pull harder on the scales, and again

notice the force readings on the scales.

5. Continue to pull on both scales, but

let the scales slowly move toward your

lab partner and then toward you at a

constant speed.

Data and Observations

1. Identify the directions of the forces on each scale.

2.

Key Concept Describe the relationship you noticed between the force readings

on the two scales.

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The Laws of Motion

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Think About This

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Content Vocabulary

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LESSON 4

Newton¡¯s Third Law

Directions: On each line, write the term from the word bank that correctly replaces the underlined words in each

sentence.

force pair

law of conservation of momentum

momentum

Newton¡¯s third law of motion

1. If two objects are moving at the same speed, the object with more mass has more of a

measure of how hard it is to stop a moving object.

2. A set of forces that two objects apply to each other does not result in a net force of zero

because each force acts on a different object.

3. The transfer of momentum between two or more objects is described by the law that

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

states that the total momentum of a group of objects remains the same unless outside

forces such as friction act on the objects.

4. The motion that occurs when a skateboarder pushes on a wall is described by the law

that states that when one object exerts a force on a second object, the second object

exerts an equal force in the opposite direction on the first object.

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Lesson Outline

LESSON 4

Newton¡¯s Third Law

A. Opposite Forces

1. When an object applies a force on another object, the second object applies a force

of the same

on the first object.

2. When an object exerts a force on another object, the second object exerts a force

on the first object in the

direction.

B. Newton¡¯s Third Law of Motion

1. According to

, when one object applies a force on a

second object, the second object applies an equal force in the opposite direction on

the first object.

2. Any time a person

against a stationary object, the

object exerts an equal and opposite force on the person.

3. A(n)

is the forces that two objects apply to each other.

a. The forces in a force pair are equal in strength and act in

directions. They do not cancel each other out because each acts on a

different

.

but opposite in

of the

action force.

C. Using Newton¡¯s Third Law of Motion

1. When you push against an object, the force you apply is called the

force.

2. Newton¡¯s third law establishes that the object you push on applies an equal and

opposite

force against you.

3. According to Newton¡¯s second law of motion, when the reaction force results in

an unbalanced force, there is a(n)

accelerates.

force, and the object

D. Momentum

1.

is a measure of how hard it is to stop a moving object.

2. Momentum is the product of an object¡¯s

its

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and

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Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

b. For every action force, there is a reaction force that is equal in

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Lesson Outline continued

3. According to Newton¡¯s second law of motion, the force on an object is equal to the

mass of the object multiplied by the acceleration, or the

in the object¡¯s velocity.

4. Because momentum is the product of mass and velocity, the force on an object

equals its change in

.

E. Conservation of Momentum

1. In any collision, one object transfers

to another object.

2. According to the

, the total momentum of a group of

objects remains the same unless outside forces act on the objects.

3. One outside force is

, which decreases the velocities of

billiard balls and most other moving objects, and they lose momentum.

4. In a(n)

collision, the colliding objects bounce off each

other.

5. In a(n)

collision, the colliding objects stick together.

6. In elastic and inelastic collisions, the total

of all the

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

objects is always the same before and after any collision.

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