essential question what are waves?a transverse wave and a longitudinal wave can combine to form...

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Lesson

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ESSENTIAL QUESTION

What are waves?By the end of this lesson, you should be able to distinguish between types of waves based on medium and direction of motion.

Waves

Ocean waves can cause great destruction. This woodblock print illustrates a great wave threatening boats off the coast of Japan.

AnswersAnswers for 1–3 should represent students’ current thoughts, even if incorrect.

1. T, F, F, T

2. Answers will vary, but should include items that produce sound or light, or that vibrate.

3. B

4. Students should define or sketch each vocabulary term in the lesson.

1

Unit 8 Introduction to Waves524

J S8P4.a Electromagnetic and mechanical waves: similarities and differences

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3 Distinguish Which of the following definitions of medium do you think is most likely to be used in the context of studying waves? Circle your answer.

A of intermediate size

B the matter in which a physical phenomenon takes place

C between two extremes

Active ReadingActive ReadingActive Reading

4 Apply As you learn the definition of each vocabulary term in this lesson, write your own definition or sketch to help you remember the meaning of the term.

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1 Predict Check T or F to show whether you think each statement is true or false.

T FThe air around you is full of waves.

Ocean waves carry water from hundreds of miles away.

Sound waves can travel across outer space.

Visible light is a wave.

2 Identify Make a list of items in the classroom that are making waves. Next to each item, write what kind of waves you think it is making. Explain your reasoning.

Engage Your Brain

Vocabulary Terms• wave

• medium

• longitudinal wave

• transverse wave

• mechanical wave

• electromagnetic wave

525Lesson 1 Waves

Quick Labs• Investigate Waves• Water Waves

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Crests

The points alongthe rope vibrateup and down. Troughs

Visualize It!

What are waves?The world is full of waves. Water waves are just one of many kinds of waves. Sound and light are also waves. A wave is a disturbance that transfers energy from one place to another.

Waves Are DisturbancesMany waves travel by disturbing a material. The material then returns to its original place. A medium is the material through which a wave travels.

You can make waves on a rope by shaking the end up and down. The rope is the medium, and the wave is the up-and-down disturbance. As the part of the rope nearest your hand moves, it causes the part next to it to move up and down too. The motion of this part of the rope causes the next part to move. In this way, the wave moves as a disturbance down the whole length of the rope.

Each piece of the rope moves up and down as a wave goes by. Then the piece of rope returns to where it was before. A wave transfers energy from one place to another. It does not transfer matter. The points where the wave is highest are called crests. The points where the wave is lowest are called troughs.

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5 Identify Underline the names for the highest and lowest points of a wave.

Active Reading

6 Label Draw an arrow near the rope to show the direction the wave travels.

Riding the Wave

The points along the rope move up and down.



Answers 5. See students’ pages for annotations

6. Students should draw an arrow coming from the hand toward the doorknob. If students recognize that the wave reflects back, then accept a double arrow.


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Waves Are a Transfer of EnergyA wave is a disturbance that transfers energy. Some waves need a medium to transfer energy, such as waves in the ocean that move through water and waves that are carried on guitar or cello strings when they vibrate. Some waves can transfer energy without a medium. One example is visible light. Light waves from the sun transfer energy to Earth across empty space.

A passing wave gives this leaf an up-and-down ride.

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7 Illustrate In the picture below, draw the leaf in the location it will be after 2 seconds.

8 Model In the space below, draw the leaf and wave as they will appear after 3 seconds.

Riding the Wave Each snapshot below shows the passage of a wave.

The leaf rises and falls as crests and troughs carry it.

Visualize It!


Answers 7. Students should draw the leaf at the

water’s surface, directly below the leaf image in the previous two illustrations.

8. Students should draw the leaf and wave so that they appear similar to the second image in the series (leaf in trough, in center of image).

Lesson 1 Waves 527


Visualize It!

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How does a wave transfer energy?A wave transfers energy in the direction it travels. However, the disturbance may not be in the same direction as the wave. Each wave can be classified by comparing the direction of the disturbance, such as the motion of the medium, with the direction the wave travels.

As a Longitudinal WaveWhen you pull back on a spring toy like the one below, you spread the coils apart and make a rarefaction. When you push forward, you squeeze the coils closer together and make a compression. The coils move back and forth as the wave passes along the spring toy. This kind of wave is called a longitudinal wave. In a longitudinal wave (lahn•jih•TOOD•n•uhl), particles move back and forth in the same direction that the wave travels, or parallel to the wave.

Sound waves are longitudinal waves. When sound waves pass through the air, particles that make up air move back and forth in the same direction that the sound waves travel.

compression rarefaction

10 Label In this longitudinal wave, label the arrow that shows the direction the wave travels with a T. Label the arrow that shows how the spring is disturbed with a D.

9 Identify As you read, underline the type of wave that sound is.

Active Reading

Different Ways to Transfer Energy

Sound waves are longitudinal waves.



Answers 9. See students’ pages for annotations.

10. The arrow near the hands should be labeled D; the arrow along the spring should be labeled T.

11. The arrow near the hands should be labeled D; the arrow along the spring should be labeled T.

12. transverse

13. P stands for primary or pressure; S stands for secondary or shear. Seismic waves are waves that travel through Earth. Body waves are seismic waves that travel through Earth’s interior. P waves are the fastest and first waves of an earthquake to be detected. S waves are second fastest and shear, or stretch, rock sideways.

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Visualize It!

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As a Transverse WaveThe same spring toy can be used to make other kinds of waves. If you move the end of the spring toy up and down, a wave also travels along the spring. In this wave, the spring’s coils move up and down as the wave passes. This kind of wave is called a transverse wave. In a transverse wave, particles move perpendicularly to the direction the wave travels.

Transverse waves and longitudinal waves often travel at different speeds in a medium. In a spring toy, longitudinal waves are usually faster. An earthquake sends both longitudinal waves (called P waves) and transverse waves (called S waves) through Earth’s crust. In this case, the longitudinal waves are also faster. During an earthquake, the faster P waves arrive first. A little while later, the S waves arrive. The S waves are slower but usually more destructive.

A transverse wave and a longitudinal wave can combine to form another kind of wave called a surface wave. Ripples on a pond are an example of a surface wave.

When these fans do “The

Wave,” they are modeling

the way a disturbance

travels through a medium.

Water waves are surface waves, a combination of transverse and longitudinal waves.

12 Categorize Is the stadium wave shown above a transverse wave or a longitudinal wave? State evidence to support your claim.

11 Label In this transverse wave, label the arrow that shows the direction the wave travels with a T. Label the arrow that shows how the spring is disturbed with a D.

Different Ways to Transfer Energy

Think Outside the Book Inquiry 13 Identify What do the letters S in

S waves and P in P waves stand for? Relate this to earthquakes and discuss it with a classmate.


529


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What are some types of waves?As you have learned, waves are disturbances that transfer energy. Waves can be classified by the direction of disturbance. But they can also be classified by what is disturbed.

Mechanical WavesMost of the waves we have talked about so far are waves in a medium. For water waves, water is the medium. For earthquake waves, Earth is the medium. A wave that requires a medium through which to travel is called a mechanical wave.

Some mechanical waves can travel through more than one medium. For example, sound waves can move through air, through water, or even through a solid wall. The waves travel at different speeds in the different media. Sound waves travel much faster in a liquid or a solid than in air.

Mechanical waves can’t travel without a medium. Suppose all the air is removed from beneath a glass dome, or bell jar, as in the photograph below. In a vacuum, there is no air to transmit sound waves. The vibrations made inside the bell jar can’t be heard.

Electromagnetic WavesAre there waves that can travel without a medium? Yes. Sunlight travels from the sun to Earth through empty space. Although light waves can travel through a medium, they can also travel without a medium. Light and similar waves are called electromagnetic (EM) waves. An electromagnetic wave is a disturbance in electric and magnetic fields. They are transverse waves. Examples of EM waves include

• visible light• radio waves• microwaves• ultraviolet (UV) light• x-raysIn empty space, all these waves travel at the

same speed. This speed, referred to as the speed of light, is about 300 million meters per second!

Making Waves

The sound from the toy cannot be heard because there is no air to transmit the sound.

Visible light is a type of wave called an electromagnetic wave.



Answers 14 Sunlight is an electromagnetic wave.

Water waves are mechanical waves.

A towel waving displays a mechanical wave.

Vocal sounds are mechanical waves. Music is a mechanical wave. Firelight is an electromagnetic wave.

530 Unit 8 Introduction to Waves


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14 Classify Identify each example of waves in these three photographs as mechanical or electromagnetic.

Sunlight is a(n)

Water waves are

A towel waving displays a(n)

Vocal sounds are

Music is a(n)

Firelight is a(n)


531


7_CFLAESE365909_1474A.aiSam Valentino08.03.10

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To complete this summary, fill in the lines below the statement to correct the statement so that it is true. You can use this page to review the main concepts of the lesson.

Visual Summary

18 Compare During a thunderstorm, you experience mechanical waves in the form of sound from thunder. You also experience electromagnetic waves in the form of light from lightning. If you were trying to compare mechanical and electromagnetic waves, what questions could you ask about thunder and lightning to develop explanations about how these two wave types are similar and how they differ?

Answers: 15 The water particles in the wave move mostly up and down; 16 The toy above shows a longitudinal wave, but the toy below shows a transverse wave; 17 This picture shows mechanical waves and electromagnetic waves (in the sunlight).

Waves are disturbances that transfer energy.

Waves can be longitudinal or transverse.

Waves can be mechanical or electromagnetic.

15 The water particles in the wave move to the right, along with the wave.

16 The toy above and the toy below both show longitudinal waves.

17 This picture shows only examples of mechanical waves.

Waves



Visual Summary Answers 15 The water particles in the wave move

mostly up and down.

16 The toy above shows a longitudinal wave, but the toy below shows a transverse wave.

17 This picture shows mechanical waves and electromagnetic waves (in the sunlight).

18 Sample answer: A leaf on the sur-face of a pond will bob up and down as waves pass, but will not move toward the shore.


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7_CFLAESE365909_1474A.aiSam Valentino08.03.10

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LessonLesson ReviewVocabularyCircle the term that best completes the following sentences.

1 A wave is a disturbance that transfers matter/energy.

2 In a longitudinal/transverse wave, the disturbance moves parallel to the direction the wave travels.

3 Mechanical/Electromagnetic waves require a medium in which to travel.

Key Concepts4–6 Identify Name the medium for each of the

following types of waves.

Type of wave Medium

ocean waves 4

earthquake waves 5

sound waves from a speaker

6

7 Describe Explain how transverse waves can be produced on a rope. Then describe how pieces of the rope move as waves pass.

8 Analyze Are the sun’s rays mechanical waves or electromagnetic waves? How do you know?

Critical Thinking9 Contrast Mechanical waves travel as

disturbances in a physical medium. Make a claim about how electromagnetic waves travel and support your thinking with evidence.

Use this image to answer the following questions.

10 Infer Even though the phone is ringing, no sound comes out of the jar. What does this tell you about the space inside the jar?

11 Claims • Evidence • Reasoning What does this same experiment tell you about light waves? Explain the evidence that supports your claim.

1


Lesson Review Answers 1 energy

2 longitudinal

3 mechanical

4 water

5 rock or Earth’s crust

6 air

7 Sample answer: A transverse wave can be made by shaking one end of a rope up and down with the other end fixed. As the wave moves down the rope, pieces of the rope move up and down.

8 The sun’s rays must be EM waves, because they travel through empty space to reach Earth.

9 EM waves travel as disturbances in electric and magnetic fields.

10 There is no air in the jar; the inside of the jar is a vacuum.

11 Light waves are EM waves that do not require a medium. They can travel through a vacuum. I know this because I can see the light from the phone.

Lesson 1 Waves 533

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My Notes

DO NOT EDIT--Changes must be made through “File info” CorrectionKey=GA-A


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essential question what are waves?a transverse wave and a longitudinal wave can combine to form...

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