The Nature. of Waves. Teacher's Guide. Visual Learning Company Editors: Brian A. Jerome, Ph.D. Stephanie Zak Jerome

Transcription

1 The Nature of Waves Teacher's Guide Editors: Brian A. Jerome, Ph.D. Stephanie Zak Jerome Assistant Editors: Anneliese Brown Louise Marrier Graphics: Lyndsey Canfield Dean Ladago Fred Thodal Union Street Brandon VT 05733

2 A Message from our Company... Visual Learning is a Vermont-based, family-owned company specializing in the creation of science programs. As former classroom science teachers, we have designed our programs to meet the needs and interests of both students and teachers. Our mission is to help educators and students meet educational goals while experiencing the thrill of science! Viewing Clearances The video and accompanying teacher s guide are for instructional use only. In showing these programs, no admission charges are to be incurred. The programs are to be utilized in face-to-face classroom instructional settings, library settings, or similar instructional settings. Duplication Rights are available, but must be negotiated with the Visual Learning Company. Television, cable, or satellite rights are also available, but must be negotiated with the. Closed circuit rights are available, and are defi ned as the use of the program beyond a single classroom but within a single campus. Institutions wishing to utilize the program in multiple campuses must purchase the multiple campus version of the program, available at a slightly higher fee. Video streaming rights are available and must be negotiated with the Visual Learning Company. Discounts may be granted to institutions interested in purchasing programs in large quantities. These discounts may be negotiated with the. Use and Copyright: The purchase of this video program entitles the user the right to reproduce or duplicate, in whole or in part, this teacher s guide and the black line master handouts for the purpose of teaching in conjunction with this video,. The right is restricted only for use with this video program. Any reproduction or duplication, in whole or in part, of this guide and student masters for any purpose other than for use with this video program is prohibited. The video and this teacher s guide are the exclusive property of the copyright holder. Copying, transmitting, or reproducing in any form, or by any means, without prior written permission from the copyright holder is prohibited (Title 17, U.S. Code Sections 501 and 506). Copyright 2008 ISBN

3 Table of Contents A Message from our Company Viewing Clearances Use and Copyright National Standards Correlations Student Learning Objectives Assessment Introducing the Program Program Viewing Suggestions Video Script Answer Key to Student Assessments Answer Key to Student Activities Pre-Test Post-Test Video Review Vocabulary Writing Activity Waves and Mediums Wave Characteristics Experimenting with Refl ection

4 National Standards Correlations Benchmarks for Science Literacy (Project AAAS) Grades 3-5 The Physical Setting - Motion (4F) By the end of 8th grade, students should know that: Vibrations in materials set up wavelike disturbances that spread away from the source. Sound and earthquake waves are examples. These and other waves move at different speeds in different materials. By the end of 12th grade, students should know that: Waves can superpose on one another, bend around corners, refl ect off surfaces, be absorbed by materials they enter, and change direction when entering a new material. All these effects vary with wavelength. The energy of waves (like any form of energy) can be changed into other forms of energy. National Science Education Standards (Content Standards: K-4, National Academy of Sciences) Physical Science - Content Standard B As a result of their activities in grades 5-8, all students should develop an understanding of: Transfer of Energy Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways. Light interacts with matter by transmission (including refraction), absorption, or scattering (including refl ection). To see an object, light from that object - emitted by or scattered from it - must enter the eye. As a result of their activities in grades 9-12, all students should develop an understanding of: Interactions of Energy and Matter Waves, including sound and seismic waves, waves on water, and light waves, have energy and can transfer energy when they interact with matter

5 Student Learning Objectives Upon viewing the video and completing the enclosed student activities, students will be able to do the following: Defi ne waves as traveling disturbances that carry energy through matter or space. Explain that waves do not actually move matter. Instead, waves fl ow through matter or create a disturbance in it. Understand that energy, often in the form of vibrations, is necessary to produce waves. Defi ne a medium as a substance, or matter through which a wave travels. Provide examples of waves traveling through the following mediums: solids, liquids, and gases (air). Sketch a simple diagram of a transverse wave. Describe how the particles in a transverse wave move across or perpendicular to the direction the wave is traveling. Explain how the particles in a longitudinal wave vibrate back and forth, parallel to the direction the wave is moving. Cite examples of transverse and longitudinal waves. Understand that waves have several different characteristics. Briefl y defi ne the following wave characteristics: - amplitude - wavelength - frequency Explain that refl ection occurs when a wave bounces back after striking something. Understand that an echo involves the refl ection of sound waves, whereas a mirror refl ects light waves. Describe refraction as the process of light changing direction, or bending, when it passes from one medium to another

6 Assessment Preliminary Test (p ): The Preliminary Test is an assessment tool designed to gain an understanding of students preexisting knowledge. It can also be used as a benchmark upon which to assess student progress based on the objectives stated on the previous pages. Post-Test (p ): The Post-Test can be utilized as an assessment tool following student completion of the program and student activities. The results of the Post-Test can be compared against the results of the Preliminary Test to assess student progress. Video Review (p. 18): The Video Review can be used as an assessment tool or as a student activity. There are two sections. The fi rst part contains questions displayed during the program. The second part consists of a fi ve-question video quiz to be answered at the end of the video

7 Introducing the Program Before showing the video program to the students ask them what enables them to see objects around the room. Next, ask them what enables them to hear your voice. Tell them that light reaching their eyes, and sound reaching their ears are in the form of waves. Explain that these are just a couple examples of waves we commonly experience. Write the term wave on the board. Ask students what the term means to them. Many will say the term means waves on the ocean or lake. Explain that a wave is a traveling disturbance that carries energy through matter or space. Tell students to pay close attention to the program to learn more about the characteristics of waves. Program Viewing Suggestions The student master Video Review (p. 18) is provided for distribution to students. You may choose to have your students complete this master while viewing the program or do so upon its conclusion. The program is approximately 14 minutes in length and includes a fi ve-question video quiz. Answers are not provided to the Video Quiz in the video, but are included in this guide on page 12. You may choose to grade student quizzes as an assessment tool or to review the answers in class. The video is content-rich with numerous vocabulary words. For this reason you may want to periodically stop the video to review and discuss new terminology and concepts

8 Video Script 1. If you have ever been to an ocean beach, you have probably enjoyed playing in the waves. 2. Maybe you ve had the thrill of surfi ng on ocean waves. 3. If you have done either of these things, then you are probably quite familiar with waves. 4. But, did you know there are many other types of waves many of which we cannot see. 5. For example, radio waves traveling invisibly through the air can be picked up by radios. 6. And sound waves enable us to hear music. 7. So, what exactly are waves? 8. What are some of the characteristics of waves? 9. And what are the different types of waves? 10. During the next few minutes we are going to explore these questions and others as we investigate the nature of waves. 12. Graphic Transition What are Waves? 13. If you have ever used a microwave oven, sailed on the ocean, or been in an earthquake, you have experienced waves. 16. What exactly is a wave? 17. A wave is a traveling disturbance that carries energy through matter or space. 18. A wave does not actually move matter. Instead, it flows through matter or creates a disturbance in it. 19. For example, sound waves travel through the air, but the air does not travel with the wave. 20. If air did travel with sound waves, you would feel a rush of air every time the phone rang! 21. Waves transfer energy from one place to another. 22. Energy, often in the form of vibrations, is necessary to produce waves. A vibration is a movement that repeatedly follows the same path. A wave is the outward movement of energy from a vibrating source. 23. You Observe! What do you notice when this guitar string is plucked? 24. You can see the string vibrating back and forth. 25. The vibrating string creates sound waves that travel through the air. We hear these sound waves as music. 26. Here is another example. As the propeller on this boat motor rapidly spins, it transfers energy to the water. 27. The propeller, along with the boat, create a wave that travels through the water. 28. Let s now take a look at the materials through which waves travel. 29. Graphic Transition Mediums and Waves 30. You have probably heard or even felt sound waves that travel through the air. 31. But did you know that sound waves can also travel through solids?

9 Video Script 32. Place your ear on a table and have someone scratch the far end of the table. You can hear the scratching sound because it traveled through the solid table. 33. Sound waves can also travel through water. Animals, like dolphins and whales, can detect sound waves hundreds of kilometers away. 34. These examples illustrate how sound waves travel through different mediums. 35. A medium is the substance, or matter, through which a wave travels. 36. Liquids, solids, and gases are all mediums. 37. Mechanical waves, such as sound waves and seismic waves those are the waves responsible for causing earthquakes need a medium through which to travel. 38. But, not all waves need to travel through a medium. 39. Electromagnetic waves, such as light, do not need a medium through which to travel. 40. For instance, in space there is little or no medium. 41. And yet, light from the sun and stars travels through the vacuum of space all the way to Earth. 42. Graphic Transition Types of Waves 43. Let s take a look at a couple of different types of waves. 44. You Decide! Describe how the waves in this rope move. 45. The waves move up and down. You might say the waves in the rope move at right angles, or perpendicularly to, the motion of the wave. 46. The wave in the rope is a type of wave called a transverse wave. 47. In a transverse wave the particles move across, or perpendicular to the direction the wave is traveling. 48. Light and other electromagnetic waves, including radio waves and microwaves, are transverse waves. 49. A longitudinal wave is another type of wave. In a longitudinal wave, particles of the medium vibrate back and forth, parallel to the direction the wave is moving. 50. This can be demonstrated with a spring-like slinky toy. 51. When the end of the spring is pushed back and forth, notice how parts of the spring are compressed and other parts are more spread apart. 52. The energy traveling through the spring creates a wave. 53. Sound waves are examples of longitudinal waves. 54. When a sound wave moves from left to right, air particles collide with other nearby air particles and form an area of compression. 55. Then the fi rst set of air particles moves to the left while the second set of particles vibrates and moves to the right. This leaves a space containing many fewer particles, called a rarefaction. As the particles compress and separate, the wave moves forward. 56. Some sound waves, such as those generated by airplanes and fireworks, can produce very powerful longitudinal waves. 58. Graphic Transition Properties of Waves 59. Waves have several different characteristics or properties, including amplitude, wavelength, and frequency

10 Video Script 60. In this diagram of a transverse wave, the high points are called crests and the low points are called troughs. Halfway between the crest and trough is the resting position. 61. The amplitude of a wave is a property that indicates how much energy a wave has. 62. Amplitude is determined by measuring the distance between a wave s resting point and its trough, or between its resting point and its crest. 63. You Compare! Which wave has a greater amplitude, wave A or wave B? 64. Wave B has a greater amplitude. 65. Waves with high amplitude, such as these huge ocean waves, have more energy than these smaller waves. 67. Wavelength is another property of waves. A wavelength is the distance between any two adjacent crests, or between any two adjacent troughs. 68. Frequency is another property. Wave frequency is the number of complete waves that pass a given point in a certain period of time. 69. When we slowly move the rope, the number of waves passing this point is low. We can say the rope has a low frequency. 70. But when we move the rope more quickly, the frequency increases. 71. Graphic Transition Interaction of Waves 72. Whenever you look in the mirror or admire the moon, you are witnessing one of the ways light interacts with matter refl ection. 74. Refl ection occurs when a wave bounces back after striking something. 75. You Observe! What do you hear after this person shouts? 76. You hear her voice again and again. 77. This is called an echo. An echo involves the refl ection of sound waves. 78. Waves usually travel in straight lines, but when they pass from one medium into another, they slow down and immediately change direction. 79. Refraction is the bending of a wave as it passes at an angle from one medium to another medium. 80. For example, when light waves travel from the air into water, they slow down and immediately change direction. 81. Refraction is responsible for causing the pencil in this glass of water to appear as if it is bent. 82. These are just a few of the many examples of wave interaction. 83. Graphic Transition Summing Up 84. During the past few minutes we have explored some of the fascinating characteristics of waves. 85. We began by learning that a wave is a disturbance that carries energy as it moves through matter or space. 86. Waves can travel through many different mediums, including solids, liquids, and gases

11 Video Script 87. We also learned that electromagnetic waves can travel without a medium, for instance, through space. 88. We discussed different types of waves, such as transverse waves and longitudinal waves. 89. The properties of waves were highlighted, including amplitude, wavelength, and frequency. 90. Finally, we investigated the various interactions of waves, including refraction and refl ection. 91. So, the next time you swim in the ocean, hear the echo of a far away noise, think about some of the things we just discussed. You might just think about waves a little differently. 94. Graphic Transition Video Assessment Fill in the correct word to complete the sentence. Good luck and let s get started. 1. transfer energy from place to place. 2. A is a movement that repeatedly follows the same path. 3. A is the substance, or matter, through which a wave travels. 4. Sound waves are examples of waves. 5. occurs when a wave bounces back after striking something

12 Answer Key to Student Assessments Pre-Test (p ) Post-Test (p ) 1. b - energy 1. b - refraction 2. d - vibrations 2. d - crest 3. c - air 3. a - echo 4. a - medium 4. d - vibrations 5. a - transverse waves 5. d - change direction 6. d - crest 6. a - medium 7. d - bounces back 7. b - energy 8. a - echo 8. a - transverse waves 9. d - change direction 9. c - air 10. b - refraction 10. d - bounces back 11. true 11. false 12. false 12. true 13. false 13. true 14. true 14. false 15. false 15. false 16. A wave is a traveling disturbance that 16. Refl ection occurs when a wave carries energy through matter or space. bounces back after striking something. 17. Most waves are produced by 17. Examples of transverse waves include vibrations in moving objects or other light, radio waves, and microwaves. matter. 18. Most waves are produced by 18. Sound can travel through solids, vibrations in moving objects or other liquids, and gases. matter. 19. Examples of transverse waves include 19. Sound can travel through solids, light, radio waves, and microwaves. liquids, and gases. 20. Refl ection occurs when a wave 20. A wave is a traveling disturbance that bounces back after striking something. carries energy through matter or space. Video Review (p. 18) 1. You can see the guitar string vibrating back and forth. 2. The waves in the rope move up and down. 3. Wave B has a greater amplitude. 4. You hear her voice again and again. This is called an echo 1. Waves transfer energy from place to place. 2. A vibration is a movement that repeatedly follows the same path. 3. A medium is the substance, or matter, through which a wave travels. 4. Sound waves are examples of longitudinal waves. 5. Reflection occurs when a wave bounces back after striking something

13 Answer Key to Student Activities Vocabulary (p. 19 ) 1. wave 2. vibration 3. medium 4. transverse wave 5. longitudinal wave 6. amplitude 7. wavelength 8. frequency 9. reflection 10. refraction Writing Activity (p. 20) If you have ever used a microwave oven, sailed on the ocean, or been in an earthquake, you have experienced waves. A wave is a traveling disturbance that carries energy through matter or space. Energy, often in the form of vibrations, is necessary to produce waves. A medium is the substance, or matter, through which a wave travels. Liquids, solids, and gases are all mediums. Light waves, microwaves, and radio waves are transverse waves. Sound waves are an example of longitudinal waves. Reflection occurs when a wave bounces back after striking something. An echo involves the refl ection of a sound wave. Waves usually travel in straight lines, but when they pass from one medium into another, they change direction in a process called refraction. Waves and Mediums (p. 21) 1. Light cannot travel through the solid (the table top). 2. Sound can travel through the air because the snap of the fi ngers could be heard. Sound could also travel through the solid such as the table top or desk top because the partner could hear the scratching. Sound also travels through water. 3. A sound wave is a longitudinal wave and a light wave is a transverse wave. A sound wave can travel through a solid whereas a light wave cannot. Wave Characteristics (p ) 1. Examples of transverse waves include light, radio waves and microwaves. 2. In a transverse wave the particles move across, or perpendicular, to the direction the wave is traveling. 3. A sound wave is an example of a longitudinal wave. 4. In a longitudinal wave, particles of the medium vibrate back and forth, parallel to the direction the wave is moving. Experimenting with Reflection (p ) Thrown straight down Directly above mirror Tennis Ball Light Thrown at angle Angled light In Your Own Words (p. 20) 1. Examples include sound waves, which enable you to listen to music and hear someone s voice, and light waves which enables us to see. 2. The crest is the highest point on a transverse wave and the trough is the lowest point. 3. Refraction is the process of a wave bending as it passes from one medium to another. 1. Refl ection is the process of an object or a wave bouncing back after making contact with an object it can t pass through. 2. According to the law of refl ection, the angle of incidence equals the angle of refl ection. In other words, the angle at which light bounces off a surface is equal to the angle at which it hits the surface. 3. Both the light and the tennis ball refl ected straight up when directed straight down. The light and the tennis ball were refl ected at an angle when directed at an angle. 4. The light would be refl ected in different directions when it hit the crumpled aluminum foil

14 Pre-Test Name Circle the best answer for each of the following questions. 1. A wave is a traveling disturbance that carries: a. water vapor b. energy c. matter d. only light 2. Waves are often created by the back and forth movements of matter called: a. energy units b. photons c. accelerations d. vibrations 3. We most commonly hear sound waves that travel through: a. Earth s core b. ocean water c. air d. plasma 4. The substance or matter through which a wave travels is a: a. medium b. space c. field d. magnetosphere 5. Light and electromagnetic waves are examples of: a. transverse waves b. longitudinal waves c. sound waves d. seismic waves 6. The highest point on a transverse wave is called its: a. trough b. amplitude c. crescent d. crest 7. Refl ection occurs when a wave strikes something and: a. penetrates it b. saturates it c. is absorbed d. bounces back 8. The refl ection of a sound wave is called a(n): a. echo b. accident c. misdirection d. transmission 9. When waves pass from one medium into another they: a. bounce back b. burn c. stop d. change direction 10. When you look at a pencil in a glass of water, the reason it looks bent is due to: a. deflection b. refraction c. absorption d. electromagnetism 14

15 Pre-Test Name Write true or false next to each statement A wave fl ows through matter but does not actually move it. Energy is not needed to produce waves. Sound cannot travel through water. Light does not need a medium through which to travel. All waves have the same wavelength. Write a short answer for each of the following. 16. What is a wave? 17. How are waves commonly produced? 18. List the three mediums through which sound can travel. 19. Give an example of a transverse wave. 20. What is refl ection? 15

16 Post-Test Name Circle the best answer for each of the following questions. 1. When you look at a pencil in a glass of water, the reason it looks bent is due to: a. deflection b. refraction c. absorption d. electromagnetism 2. The highest point on a transverse wave is called its: a. trough b. amplitude c. crescent d. crest 3. The refl ection of a sound wave is called a(n): a. echo b. accident c. misdirection d. transmission 4. Waves are often created by the back and forth movements of matter called: a. energy units b. photons c. accelerations d. vibrations 5. When waves pass from one medium into another they: a. bounce back b. burn c. stop d. change direction 6. The substance or matter through which a wave travels is a: a. medium b. space c. field d. magnetosphere 7. A wave is a traveling disturbance that carries: a. water vapor b. energy c. matter d. only light 8. Light and electromagnetic waves are examples of: a. transverse waves b. longitudinal waves c. sound waves d. seismic waves 9. We most commonly hear sound waves that travel through: a. Earth s core b. ocean water c. air d. plasma 10. Refl ection occurs when a wave strikes something and: a. penetrates it b. saturates it c. is absorbed d. bounces back 16

17 Post-Test Name Write true or false next to each statement All waves have the same wavelength. Light does not need a medium through which to travel. 13. A wave fl ows through matter but does not actually move it. 14. Energy is not needed to produce waves. 15. Sound cannot travel through water. Write a short answer for each of the following. 16. What is refl ection? 17. Give an example of a transverse wave. 18. How are most waves produced? 19. List the three mediums through which sound can travel. 20. What is a wave? 17

18 Video Review Name While you watch the video, answer these questions: You Observe! 1. What do you notice when this guitar string is plucked? You Decide! 2. Describe how the waves in this rope move. You Compare! 3. Which wave has a greater amplitude, wave A or wave B? You Observe! 4. What do you hear after this person shouts? After you watch the video, test your knowledge with these questions. 1. transfer energy from place to place. 2. A is a movement that repeatedly follows the same path. 3. A is the substance, or matter, through which a wave travels. 4. Sound waves are examples of waves. 5. occurs when a wave bounces back after striking something. 18

19 Vocabulary Name Use these words to fill in the blanks next to the sentences below. Words transverse wave medium refl ection amplitude frequency vibration wavelength refraction wave longitudinal wave 1. A travelling disturbance that carries energy through matter or space. 2. A repeated back and forth movement of matter; often necessary to produce waves. 3. A substance or matter through which a wave travels. 4. A type of wave in which particles move across or perpendicular to the direction the wave is traveling. 5. A type of wave in which particles of the medium vibrate back and forth. 6. The distance between a wave s resting point and its trough or crest. 7. The distance between any two adjacent wave crests or any two adjacent wave troughs. 8. The number of complete waves that pass a point in a certain period of time. 9. Occurs when a wave bounces back after striking something. 10. Occurs when a wave passes from one medium into another and changes direction. 19

20 Writing Activity Name Words transverse waves refl ection energy medium echo longitudinal waves refraction waves vibrations gases Use the correct word from above to complete the sentences in the following paragraph. If you have ever used a microwave oven, sailed on the ocean, or been in an earthquake, you have experienced. A wave is a traveling disturbance that carries through matter or space. Energy, often in the form of, is necessary to produce waves. A is the substance, or matter, through which a wave travels. Liquids, solids, and are all mediums. Light waves, microwaves, and radio waves are. Sound waves are an example of. occurs when a wave bounces back after striking something. An involves the refl ection of a sound wave. Waves usually travel in straight lines, but when they pass from one medium into another, they change direction in a process called. In Your Own Words 1. List two ways you benefi t from waves. 2. What is the difference between the crest and trough of a transverse wave? 3. What is refraction? 20

21 Waves and Mediums Name Have you ever laid your ear down on a table and heard sounds travel through the table? Or have you ever seen light shine through water? Both of these examples illustrate how waves can travel through different mediums. A medium is the substance, or matter, through which a wave travels. Liquids, solids, and gases are all mediums. In this activity you will experiment with light (a transverse wave) and sound (a longitudinal wave) to see how they travel through different mediums. Materials: fl ashlight, table, glass beaker, and water Directions: Light 1. Obtain a fl ashlight. 2. Begin by seeing if light travels through air. Turn off the lights and darken the room. Turn on the fl ashlight. Can its light be seen? Does light travel through air? Record your observations below in the table. 3. Point the fl ashlight at a table top. Does the light pass through it? Record your observations in the table below. 4. Fill a glass beaker with water. Darken the room. Hold the fl ashlight close to the side of the beaker and point it through the beaker. Does light go through the water? Record your observations. Directions: Sound 1. Snap your fi ngers. Can you hear the snap? Record your observations. 2. Obtain a large beaker of water or fi sh tank full of water. Place your hand underwater and snap your fi ngers. Place your ear close to the surface of the water. Can you hear the sound travel through the water? Record your observations. 3. Have your partner put their ear down fl at against a table top or desk top. Move to the opposite end of the table or desk and lightly scratch it. Can your partner hear your scratching? Record your observations. Air Liquid Solid Light Sound Questions: 1. Which medium can light not travel through? 2. Which medium(s) can sound travel through? How do you know this? 3. How is a sound wave different from a light wave? 21

22 Wave Characteristics Name Background: Whenever you listen to music, use a fl ashlight, or warm something in a microwave oven, you are using waves. A wave is a traveling disturbance that carries energy through matter or space. Waves transfer energy from one place to another. In this activity you will explore the characteristics of two different types of waves: transverse waves and longitudinal waves. In a transverse wave, the particles move across, or perpendicular to, the direction the wave is traveling. Light, radio waves, and microwaves are transverse waves. In a longitudinal wave, particles of the medium vibrate back and forth, parallel to the direction the wave is moving. Sound waves are examples of longitudinal waves. When a sound wave moves from left to right, air particles collide with other nearby air particles and form an area of compression. Then the fi rst set of air particles moves to the right. This leaves a space containing many fewer particles, called rarefaction. Waves have several different characteristics or properties, including amplitude, wavelength, and frequency. Following is a brief description of these properties: amplitude - distance between a wave s resting point and trough or crest. wavelength - distance between any two adjacent crests or any two adjacent troughs. frequency - the number of complete waves that pass a given point in a certain period of time. Directions: There are sketches of a transverse wave and longitudinal wave on the next page. On the transverse wave, identify the crest, trough, amplitude, and wavelength. On the longitudinal wave, label the compression, rarefaction, and wavelength. 22

23 Wave Characteristics Name Questions: 1. List two examples of transverse waves. 2. Describe the motion of particles in a transverse wave. 3. Give an example of a longitudinal wave. 4. Describe the motion of particles in a longitudinal wave. 23

24 Experimenting with Reflection Name Background: If you have ever played pool or tennis, you know how important it is to understand how balls bounce back after hitting something. Refl ection is the process of an object or a wave bouncing back after making contact with an object it can t pass through. Light can also be refl ected. Whenever you look into a mirror, you are benefi ting from the refl ection of light. When you throw a tennis ball straight down it bounces straight up. But, if you throw it at an angle, it bounces away at an angle. Light behaves similarly. The angle at which light hits an object is called the angle of incidence. The angle at which light bounces off an object is called the angle of refl ection. According to the law of refl ection, the angle of incidence equals the angle of refl ection. In other words, the angle at which light bounces off a surface is equal to the angle at which it hits the surface. In this activity you will experiment with the law of refl ection. Materials: tennis ball flashlight (with narrow beam) or laser pointer mirror talcum power (baby powder) Directions: 1. Work in pairs. Obtain a tennis ball. 2. Gently bounce a tennis ball straight down toward the fl oor. Observe how the tennis ball reflects (bounces back). 3. There are four blank boxes on the following page. In the appropriate space, draw the path and angle at which the tennis ball was thrown and refl ected. 4. Now gently throw the ball at an angle and have your partner catch it. 5. In the appropriate space, draw the path and angle at which the tennis ball was thrown and reflected. 6. Now obtain a fl ashlight with a narrow beam or a laser pointer and a mirror. 7. Lay the mirror fl at on a table. Turn off the lights. Gently create a fi ne dust cloud of talcum powder above the mirror. 8. Quickly turn on the flashlight and point it directly toward the mirror from above. Observe how the beam of light is refl ected. 9. In the appropriate space, draw the path of the beam of light. 10. Turn off the lights. Once again create a fi ne dust cloud of talcum powder above the mirror. 11. Direct the beam of light at an angle toward the mirror. Observe the refl ected beam of light. 12. In the appropriate space, draw the path of the light beam and label the angle of incidence and reflection. 24

25 Experimenting with Reflection Thrown straight down Name Tennis Ball Thrown at angle Directly above mirror Light Angled light Questions: 1. What is refl ection? 2. Describe the law of refl ection. 3. How did light behave like the tennis ball? 4. What would happen to the refl ection of light if it hit a crumpled piece of aluminum foil? 25