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28 Unit 1 • Energy

Look at the photos. Discuss the photos with your partner. Describe the photos.

How are the two photos the same? How are they different?

Lesson 3

Waves

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Lesson 3 • Waves 29

The photos on this page are similar to the photos on the last page, but there are differences, too. Look closely. Discuss the photos with your partner. How are the photos similar to the photos on the first page of this lesson? How are they different?

Which pair of waves do you think has more energy—the waves on the first page of this lesson or the waves on the second page? Explain your answer.

Look AheadHow do waves travel? Where do waves get their energy? You will learn more about waves and energy in this lesson.

Explore!

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30 Unit 1 • Energy

Wave MovementMaterials• Laundry line (thin rope) about 2 meters long• Black tape or thick black marker

Steps

Hold one end of the rope in your hand. Give the other end to one of your teammates. Walk away from your partner until the rope is above the floor but not stretched tight. As your third teammate watches, move your hand up and down gently, over and over again. Your partner should hold the other end of the rope still. Trade spots so that everyone has a chance to move and watch the rope.

Describe what the rope did when your teammates moved their hands up and down.

Describe how the rope moves differently when you move it at different speeds or from different heights.

Wrap some black tape or make a thick black mark around the rope at the halfway point. Work with your teammates to move the rope up and down again. When it is your turn to observe, watch the tape or black mark.

How is the movement of the rope different from the movement of the tape or black mark?

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Lesson 3 • Waves 31

Think About It

When you moved the rope up and down, you were creating waves. The energy needed to make the waves came from your arms.

Which waves had the least amount of energy? Which had the most?

Imagine you wanted to make an enormous wave with your rope. What would you need to do? Talk about your ideas with your group. Explain your reasoning.

Imagine you wanted to make lots of little waves with your rope. What would you need to do? Talk about your ideas with your group. Explain your reasoning.

Share your thoughts with the other members of your group, and listen to their ideas. Then use the lines below to write your final ideas.

32 Unit 1 • Energy

Understand

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32 Unit 1 • Energy

As a wave moves, it carries energy. The rope carried energy in waves from your arm to your classmate’s arm.

Ocean waves are usually caused by something disturbing the surface of the water. Wind is the most common cause of ocean waves. Wind is moving air. As the wind hits the surface of the ocean water, it transfers motion energy to the water. This energy moves through the water in the form of waves.

Compare the waves in the two photos above. What do you think caused the differences in the waves?

A model represents, or stands for, something else. Think back to the Explore activity. Describe how the activity was a model for the motion and energy of ocean waves.

Lesson 3 • Waves 33

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Lesson 3 • Waves 33

Waves can be tall or short. The tops of waves can be close together or far apart. The diagram below shows how scientists measure waves.

AmplitudeWavelength

Wavelength

The height of a wave is called its amplitude. The distance between the tops or bottoms of two waves is called wavelength. Waves with high amplitude and short wavelengths have more energy. Waves with low amplitude and long wavelengths have less energy.

A pattern is something that repeats itself. Waves are patterns of motion. The diagrams below show two different wave patterns.

Describe the two wave patterns shown above. Use the words amplitude and wavelength in your answer.

Which waves have more energy? Explain your answer.

34 Unit 1 • Energy

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34 Unit 1 • Energy

Imagine the waves you just described are ocean waves. Which waves would you most likely see on a calm, sunny day? Why?

Waves transport energy, but they do not transport objects. Boats in the ocean move up and down on waves, but the waves do not move boats from place to place. That is because water does not move along with the waves. When waves move through it, water just moves up and down in the same place.

Think back to your experiment with the rope. Waves moved along the rope, but the mark on the rope did not move forward. Only energy moved along the path of the rope.

In which direction will the waves move the boat? Explain your answer.

Lesson 3 • Waves 35

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Lesson 3 • Waves 35

The ocean is not the only place where you can find water waves. They also occur in lakes, rivers, ponds, and even puddles. Some waves move in lines, and others move in circles.

Study the photo above. What kind of place do you think the photo shows? What energy transfer caused the waves to form? Explain your ideas.

Study the photo above. What kind of place do you think the photo shows? What energy transfer caused the waves to form? Explain your ideas.

36 Unit 1 • Energy36 Unit 1 • Energy

Try This

Recall that a model stands for something else. In this lesson, you used a rope to make a model of a water wave. The diagrams of waves on page 33 are also models. Think about how those models helped you understand waves.

Fill a cup about halfway with water. Blow on the water gently.

Describe what you observe.

Blow on the water harder.

Describe what you observe.

Explain how this activity can be a model for how waves form in the ocean. Use the word energy in your answer.

Talk about the model with a partner. Is it easier or harder to study the model instead of real ocean waves? Explain your ideas.

Lesson 3 • Waves 37

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Check YourUnderstanding

Lesson 3 • Waves 37

1 Which wave has the greatest amount of energy?

A

B

C

D

2 How did you decide which diagram to choose in question 1 above? Explain your reasoning.

3 What happens to an object that is sitting on a wave?

A It moves backward.

B It moves forward.

C It goes back and forth.

D It goes up and down.

4 Which of the following statements about waves is true?

A Waves are all the same size.

B Waves move objects from one place to another.

C We measure the height of waves to find their amplitude.

D We measure the height of waves to find their wavelength.