Chap01 Science Answer Key

Explore Activity: Observe wavebehavior, p. 7 Before You Read, p. 7 MiniLAB: Comparing Sounds, p. 11 Physics Integration, p. 12 Health Integration, p. 16 Science Online, p. 17 Activity: Waves on a Spring, p.18 MiniLAB: Observing How Light Refracts, p. 20 Science Online, p. 23 Problem-Solving Activity: Can you create destructive interference?, p. 23 Visualizing Interference, p. 24 Activity: Wave Speed, pp. 26–27 Science Stats: Waves, Waves, and More Waves, pp. 28–29 Chapter Opener Section 1 What are waves? 4 sessions 2 blocks 1. Explain the relationship among waves, energy, and matter. 2. Describe the difference between transverse waves and compressional waves. Section 2 Wave Properties 4 sessions 2 blocks 1. Describe the relationship between the frequency and wavelength of a wave. 2. Explain why waves travel at different speeds. Section 3 Wave Behavior 5 sessions 2.5 blocks 1. Explain how waves can reflect from some surfaces. 2. Explain how waves change direction when they move from one material into another. 3. Describe how waves are able to bend around barriers. See p. 7T for a Key to Standards. National Content Standards: UCP5, A1, B1, B3 National Content Standards: UCP3, A1, B3 National Content Standards: UCP2, A1, B1, B3 National State/Local Section/Objectives Standards Activities/Features 6A N O CHAPTER 1 Waves CHAPTER WAVES 1 1 Section Focus Transparency Teaching Transparency Interactive CD-ROM/DVD Guided Reading Audio Program Section Focus Transparency Interactive CD-ROM/DVD Guided Reading Audio Program Section Focus Transparency Interactive CD-ROM/DVD Guided Reading Audio Program Chapter Resources Booklet Foldables Worksheet, p. 15 Directed Reading Overview, p. 17 Note-taking Worksheets, pp. 31–32 Chapter Resources Booklet Transparency Activity, p. 42 MiniLAB, p. 3 Enrichment, p. 28 Reinforcement, p. 25 Directed Reading, p. 18 Transparency Activity, pp. 45–46 Chapter Resources Booklet Transparency Activity, p. 43 Enrichment, p. 29 Reinforcement, p. 26 Directed Reading, p. 19 Activity Worksheet, pp. 5–6 Lab Activity, pp. 9–11 Reading and Writing Skill Activities, p. 33 Home and Community Involvement, p. 42 Chapter Resources Booklet Transparency Activity, p. 44 Enrichment, p. 30 Reinforcement, p. 27 Directed Reading, pp. 19, 20 MiniLAB, p. 4 Lab Activity, pp. 13–14 Activity Worksheet, pp. 7–8 Lab Management and Safety, p. 65 Mathematics Skill Activities, p. 47 Portfolio Activity, p. 10 Performance MiniLAB, p. 11 Skill Builder Activities, p. 12 Content Section Assessment, p. 12 Portfolio Extension, p. 14 Science Journal, p. 16 Performance Skill Builder Activities, p. 17 Content Section Assessment, p. 17 Portfolio Challenge, p. 25 Performance MiniLAB, p. 20 Problem-Solving Activity, p. 23 Skill Builder Activities, p. 25 Content Section Assessment, p. 25 Explore Activity: clear plastic plate, a cork or straw, dropper, 1 cm water MiniLAB: wooden ruler Activity: long, coiled spring toy, 5 cm colored yarn, meterstick, stopwatch MiniLAB: large, opaque drinking glass or cup, water, white soda straw Activity: coiled spring toy, stopwatch, meterstick, tape CHAPTER 1 Chapter Organizer O N 6B Activity Materials Reproducible Resources Section Assessment Technology CHAPTER ORGANI ZER Need materials? Contact Science Kit at 1-800-828-7777 or www.sciencekit.com on the Internet. Chapter Resources Booklet Chapter Review, pp. 35–36 Chapter Tests, pp. 37–40 Standardized Test Practice by The Princeton Review, pp. 7–10 MindJogger Videoquiz CD-ROM Explorations and Quizzes Vocabulary Puzzle Makers ExamView Pro Test Bank Interactive Lesson Planner Interactive Teacher’s Edition Performance Assessment in the Science Classroom (PASC) End of Chapter Assessment Blackline Masters Technology Professional Series CHAPTER WAVES 1 1 Hands-on Activities Laboratory Activities Activity Worksheets Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Waves 5 Name Date Class Lab Preview Directions: Answer these questions before you begin the Activity. 1. Why should you wear goggles when performing this activity? 2. How do you use yarn in this activity? Waves are rhythmic disturbances that carry energy through matter or space. Studying waves can help you understand how the Sun’s energy reaches Earth and sounds travel through the air. What You’ll Investigate What are some of the properties of transverse and compressional waves on a coiled spring? Materials long, coiled spring toy colored yarn (5 cm) meterstick stopwatch Goals I Create transverse and compressional waves on a coiled spring toy. I Investigate wave properties such as speed and amplitude. Safety Precautions CAUTION: Avoid over-stretching or tangling the spring to prevent damage. Procedure 1. Work in pairs or groups and clear a place on an uncarpeted floor about 6 m ✕ 2 m. 2. Stretch the springs between two people to the length suggested by your teacher. Measure the length. 3. Create a wave with a quick sideways snap of the wrist. Time several waves as they travel the length of the spring. Record the average time in the data table in the Data and Observations section. 4. Repeat step 3 using waves that have slightly larger amplitudes. 5. Squeeze together about 20 of the coils. Observe what happens to the unsqueezed coils. Release the coils and observe. 6. Quickly push the spring toward your partner, then pull it back. 7. Tie the yarn to a coil near the middle of the spring. Repeat step 7 observing the string. Waves on a Spring H a n d s -O n A c t iv it ie s L2 Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Waves 13 Name Date Class Waves enable you to see this page and to hear voices. Waves carry energy fromone place to another without carrying matter. Waves often bounce off objects (reflection), change direction when they travel fromone mediumto another (refraction), and spread around barriers (diffraction). Strategy You will simulate the behaviors of waves. You will observe and study how waves reflect, refract, and diffract. Materials rectangular, clear plastic storage box glass plate wood block (15 cm ✕ 3 cm ✕ 7 cm) support clips for glass plate (4) to use as wave generator paraffin block (4 cm ✕ 4 cm ✕ 1 cm) steel barrier (1 m ✕ 4 cm ✕ 1 cm) paraffin blocks, 2 (10 cm ✕ 6 cm ✕ 1 cm) Procedure 1. Fill the box with water to a depth of 3 cm. 2. Hold the wooden block in the water so that it is just touching the bottom near one end of the box and is parallel with the side of the box. Lift the block out of the water. This entire motion should take about 1 s. Repeat the motion until you can produce uniform waves. 3. Once you are satisfied that you can produce uniform waves, set up the other simulations as illustrated in the diagrams. Each simulation will take at least 5 min. During that period of time, observe the waves and their behavior. 4. After you have finished the simulations, answer the following questions. Laboratory Activities 2 2 H a n d s -O n A c t iv it ie s Wave Reflection, Refraction, and Diffraction Questions and Conclusions Simulation A 1. Describe the behavior of the waves before and after they reflected from the steel barrier. 2. Change the angle of the barrier and repeat.. What happens to the direction of the reflected waves? Simulation B 3. When the waves passed over the glass plate, they entered shallower water. What happened to their speed? 4. The change in speed simulates what happens when a wave passes from one medium into another. How was the direction of the wave affected? 5. The change in direction of a wave when it passes from one medium into another is called refraction, and the line drawn perpendicular to the edge of the plate is called the normal. Did the water waves bend away from the normal or toward it when they passed over the plate? L2 Hands-on Activities Transparencies Section Focus Waves Surfing may seemlike a fairly new sport, but it’s not. In fact, people think there were surfers in Hawaii in the 1400s. When Captain Cook landed in the Hawaiian Islands in 1778, he was greeted by an islander on a surfboard! Ride the wave! Section Focus Transparency 1 1 1. Name some different kinds of waves. 2. When waves travel through a medium, is any material moved along? Illustrate your answer with an example. 3. What type of waves do not require a mediumfor travel? 7 Chapter Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. L2 Waves Visible light and ultraviolet (UV) radiation both come from the Sun. UV radiation causes eye damage, skin cancer, and burns skin. Visible light and UV radiation are the same type of wave; the difference between the two is their wavelengths. The Sun’s Radiant Energies Section Focus Transparency 2 2 1. How are visible light and UV radiation the same? 2. How can you protect yourself fromthe harmful consequences of UV radiation? 7 Chapter Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. L2 Waves Artists work with all kinds of materials, so why not water? This image was made by placing an obstacle in the water and generating waves. As waves reach the obstacle, they move through the holes. Wave Art Section Focus Transparency 3 3 1. Describe what is happening in this picture. 2. What would happen to the wave pattern if both holes were plugged? 3. Do you think sound waves diffract in a similar fashion? Give an example that illustrates your answer. 7 Chapter Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. L2 Transparencies Teaching Assessment Waves Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Directions: Carefully reviewthe graph and answer the following questions. Waves 1. According to these data, which type of animal might hear a few sounds with frequencies lower than 10 Hertz? A Bat B Dog C Grasshopper D Human 2. According to the graph, which type of animal has the smallest hearing range? F Bat G Cat H Dolphin J Grasshopper 3. About how much greater is the highest frequency of sound that cats can hear than the highest frequency of sound that dogs can hear? A 200 Hertz C 20,000 Hertz B 2,000 Hertz D 200,000 Hertz 4. According to this information, which type of animal can hear sounds with frequencies higher than 100,000 Hertz? F Bat H Dolphin G Cat J Human Assessment Transparency Optimal Hearing Range of Animals G rasshopper Bat Cat D og D olphin H um an 10 100 1,000 10,000 100,000 H e rtz Type of Animal 7 Chapter L2 Waves Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Compression and Rarefaction C o m p r e s s io n R a r e fa c t io n C o m p r e s s io n M o le c u le s t h a t m a k e u p a ir Teaching Transparency 1 1 7 Chapter L2 The following designations will help you decide which activities are appropriate for your students. Level 1 activities should be appropriate for students with learning difficulties. Level 2 activities should be within the ability range of all students. Level 3 activities are designed for above-average students. ELL activities should be within the ability range of English Language Learners. Cooperative Learning activities are designed for small group work. Multiple Learning Styles logos are used throughout to indicate strategies that address different learning styles. These strategies represent student products that can be placed into a best-work portfolio. P LS COOP LEARN ELL L3 L2 L1 Key to Teaching Strategies This is a representation of key blackline masters available in the Teacher Classroom Resources. See Resource Manager boxes within the chapter for additional information. 6C N O CHAPTER 1 Waves RESOURCE MANAGER Spanish Directed Reading Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Name Date Class Waves 21 M e e t in g In d iv id u a l N e e d s Sinopsis Ondas Instrucciones: Usa los siguientes términos para completar el mapa conceptual. energía ondas transversales ondas mecánicas amplitud longitud de onda freqcuencia Instrucciones: Completa las siguientes oraciones usando el término correcto. 7. Cuando una onda choca contra un medio y cambia de dirección, se conoce como ____________________. 8. La capacidad de dos ondas de combinarse y traslaparse se llama ____________________. 9. Un eco es un ejamplo de una onda sonora ____________________. 10. La desviación de las ondas alrededor de un obstáculo se conoce como ____________________. a través del espa- cio en forma de transportan pueden describirse por sus 1. Las ondas ondas electromag- néticas que pueden ser 2. 3. ondas de compresión 4. 5. 6. de de de propiedades a través de la ma- teria en forma de Lectura Dirigida para la Maestría del Contenido L1 Enrichment 28 Waves Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Name Date Class Seismic Waves Waves that transfer energy through Earth are seismic waves. They occur when energy that has been building up inside Earth is released. Sudden motion causes shock waves that radiate out form the area of rupture. The movement of parts of Earth as these waves travel is called an earthquake. Seismic waves do not travel symmetrically in all directions. There are two main types of seismic waves: longitudinal waves called P (Primary) waves and S (Secondary) or shear waves. Primary waves pro- duce ground motion back and forth in the direc- tion of wave travel. Secondary waves vibrate the ground perpendicular to the direction of travel. Seismic waves are not all alike. How far they travel and how intense they are depend on two things. One is how much energy is released. The other is the kind of material the wave passes through. Materials can vary in terms of depth, the type of rock that’s pre- sent, and the soil conditions.As seismic waves travel farther from the rupture, they become less intense. Near the site where the shift takes place, a large amount of energy that is released produces shocks, jolts, and roaring noise. Farther away, the movement becomes more rolling and the sound becomes more like a rumble. Enrichment 1 1 Directions: Answer the following questions using complete sentences. 1. Are seismic waves mechanical or electromagnetic waves? Are seismic waves transverse or com- pressional waves? 2. Why do you think an earthquake is accompanied by noise? P S L Primary waves Secondary waves Long (surface) waves L3 Meeting Different Ability Levels Directed Reading Reinforcement Content Outline Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Name Date Class Waves 31 Waves Section 1 What are waves? A. Rhythmic disturbances that carry energy without carrying matter are called ______________. B. Molecules ___________________ wave energy without themselves moving, like a line of people passing a ball. C. ____________________ waves use matter to transfer energy. 1. In a ____________________ wave, the wave energy causes the matter in the medium to move up and down or back and forth at right angles to the direction the wave travels. 2. In a ____________________________, matter in the medium moves forward and back- ward in the same direction the wave travels. D. _______________ waves are compressional waves caused by colliding air molecules transferring energy to each other. E. _________________________ waves transfer energy without using matter; transverse waves that are produced by electrically charged particles. Section 2 Wave Properties A. ___________________—a measure of how high crests are; the greater the amplitude, the more energy a wave carries B. The distance from the top of one crest to the top of the next one or from the bottom of one trough to the bottom of the next one is called ____________________. C. ___________________—number of wavelengths passing a given point per second 1. Longer wavelengths result in _________________ frequencies. 2. ________________ frequencies result in shorter wavelengths. 3. _______________ and _______________ result from wavelengths and frequencies of light and sound. D. Wave _______________—how fast a wave travels through a medium 1. Mechanical waves travel faster in a medium in which atoms are ________________ together. 2. Electromagnetic waves travel faster in a medium with _______________ atoms in it. M e e t in g In d iv id u a l N e e d s Note-taking Worksheet Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Name Date Class Waves 25 Directions: Write the kind or kinds of waves—mechanical, electromagnetic, transverse, or compressional—that apply to each term or description. 1. has areas where particles are spread out 2. water waves 3. X rays 4. transfer energy but not matter 5. has peaks and valleys 6. can travel only through a medium 7. can travel through a vacuum 8. matter moves in same direction as wave travels 9. matter moves at right angles to direction wave travels Directions: Study each of the following diagrams. Then label each one and give an example of each kind of wave. What are waves? M e e t in g In d iv id u a l N e e d s Reinforcement 1 1 14. 15. 11. 10. 13. Example: 17. Example: A. B. 12. wave 16. wave Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Name Date Class Waves 17 Content Mastery Overview Waves Directions: Use the following terms to complete the concept map below. energy transverse waves mechanical waves amplitude wavelength frequency M e e t in g In d iv id u a l N e e d s Directions: Complete the following sentences using the correct terms. 7. When a wave hits a new medium and changes direction, it is called ____________________. 8. When two waves meet and overlap it is called ____________________. 9. An echo is an example of sound wave ____________________. 10. The bending of waves around a barrier is called ____________________. through space as carry can be desribed by 1. Waves electromagnetic waves through matter as which can be 2. 3. compression waves 4. 5. 6. of of of properties Meeting Different Ability Levels L2 L2 L1 Chapter Tests Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Name Date Class Waves 37 Chapter Test Waves I. Testing Concepts Directions: For each of the following, write the letter of the termor phrase that best completes the sentence. 1. Waves can ______ when they move from one medium to another. a. disappear b. interfere c. bend d. split 2. A(n) ______wave DOES NOT need matter for energy transfer. a. electromagnetic b. mechanical c. compressional d. sound 3. In a mechanical ______ wave, matter moves at a right angle to the wave direction. a. compressional b. transverse c. light d. electromagnetic 4. The speed of sound in water is ______ the speed of sound in air. a. greater than b. less than c. equal to d. not greater than 5. A region of spread-out particles in a compressional wave is called a(n) ______. a. compression b. rarefaction c. interference d. medium 6. Waves can combine with each other; this is called ______. a. interference b. wave addition c. compression d. rarefaction 7. Wave frequency is the ______ of waves passing a given point per second. a. amplitude b. wavelength c. speed d. number 8. In a(n) ______wave, matter moves back and forth in the same direction as the wave. a. compressional b. transverse c. light d. electromagnetic 9. The action of a wave bouncing off a surface is called ______. a. rarefaction b. refraction c. reflection d. diffraction 10. Amplitude reflects the amount of ______ in a wave. a. energy b. compression c. rarefaction d. speed 11. A(n) ______ is the distance between a point on one wave and the identical point on the next wave. a. amplitude b. wavelength c. frequency d. compression 12. The ______ of waves can change when the waves move from one medium to another. a. altitude b. amplitude c. speed d. compression 13. A mechanical wave can travel only through ______. a. air b. water c. matter d. a vacuum 14. The action of a wave bending around a barrier is called ______. a. reflection b. diffraction c. refraction d. rarefaction 15. For significant ______ to occur, the wavelengths should match the size of the open- ing they are passing through. a. reflection b. diffraction c. refraction d. rarefaction A s s e s s m e n t L2 Chapter Review Test Practice Workbook L2 Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Name Date Class Waves 35 Chapter Review Waves Part A. Vocabulary Review Directions: Match the terms in Column II with the definitions in Column I. Write the letter of the correct termin the blank at the left. Column I 1. Squeezing a group of particles in a wave 2. A transverse or compressional wave that can travel only through matter 3. The matter through which a wave transfers energy 4. A wave bends around a barrier 5. A mechanical wave in which matter moves at right angles to the wave direction 6. A wave in which matter moves back and forth in the direction the wave is moving 7. A wave that doesn’t require matter to transfer energy 8. A region of spread-out particles in a wave 9. The distance from the crest or trough of a wave to the rest position 10. The action of a wave bouncing off an object 11. The number of waves passing a given point per second 12. The product of wavelength and frequency 13. A combination of waves form a smaller wave 14. A combination of waves form a larger wave 15. A rhythmic disturbance that carries energy 16. A wave bends as it moves from one medium to another 17. The distance between a point on a wave and the identical point on the next wave Column II a. amplitude b. compression c. compressional wave d. diffraction e. electromagnetic wave f. frequency g. constructive interference h. destructive interference i. mechanical wave j. medium k. wave speed l. rarefaction m. reflection n. refraction o. transverse wave p. wave q. wavelength A s s e s s m e n t L2 Assessment Assessment CHAPTER 1 Resource Manager O N 6D the waves interfere. The ratios of the frequen- cies of the tones determine whether or not they are pleasing. Wave Behavior Reflection The angle of incidence (the incoming wave angle) equals the angle of reflection (the outgoing wave angle). This is known as the law of reflection. The angles of incidence and reflection are measured relative to a line drawn perpendicular to the reflecting surface. Diffuse reflection occurs as the light bounces at different angles from uneven surfaces. Diffuse reflection makes the uneven surfaces appear dull. Refraction In the case of light waves, a constant called a substance’s index of refraction is the speed of light in a vacuum divided by the speed of light in the substance. The index of refraction gives the ratio between the sine of the angle of inci- dence and the sine of the angle of refraction. Refraction can be beneficial. For example, eyeglasses and contact lenses correct vision by refracting light rays so that they focus properly on the retina of the eye. Binoculars, micro- scopes, and telescopes also utilize refraction to produce magnified images of small objects and objects at great distances. Diffraction The phenomenon called diffraction occurs as waves bend around barriers or spread through apertures. Diffraction of light can produce fringes (a series of bright and dark lines) as light waves bend around the edges of objects such as razor blades, diffraction gratings, or the teeth of a comb. The fringes, which can be seen on a screen, are a series of constructive and destructive interference patterns. As the light passes through the aperture, each point on the aperture can be considered a new point source CHAPTER WAVES 1 1 6E N O CHAPTER 1 Waves What are waves? What is a wave? Electromagnetic waves have a dual nature. In describing their emission from matter or absorption by matter, they are best described as particles, usually called photons. During their propagation, they are best described as waves. In electromagnetic waves, which are always transverse, electric and magnetic fields oscillate perpendicular to the direction the waves travel. Wave Properties Wave Movements Waves travel outward from an energy source. If a rock is thrown into a pond, energy traveling outward from the center is seen as waves, dampening (decreasing in amplitude) as they move through the molecules of water. The wave will move through one complete cycle in one wavelength. The period (T) of a wave is the time it takes one wavelength to pass a fixed point. A wave’s period is the reciprocal of its frequency. Light waves are electromag- netic waves. Visible light has a range of wavelengths between about 400 nm and 700 nm. We know the elements present in stars by the wavelengths of light they emit, which are detected by spectroscopes. The speed of light in a vacuum is constant at about 3 ϫ 10 8 m/s. Michelson and Morley accurately measured the speed of light by reflecting light rays from a moun- taintop to a rotating mirror. The amplitude of a sound wave determines its sound intensity, or how loud it is. The more sound energy generated, the louder the sound. Two or more tones produced at the same time produce unpleasant (dissonant) or pleasant (harmonious) sounds, depending on the way 1 1 S E C T I O N 3 3 S E C T I O N Massive bodies have strong gravita- tional fields. If these bodies undergo some sort of regular motion, oscillations in their gravity fields can, according to theory, be detected. Scientists are currently trying to develop methods of detecting these gravity waves. 2 2 S E C T I O N CHAPTER 1 Helping You Prepare O N 6F HELPI NG YOU PREPARE of light, a concept known as Huygens’ princi- ple. The light reaching a particular point on the screen comes from different points on the aperture, and thus has traveled different dis- tances to the screen. The interference patterns are produced because at different points the phases of the waves add constructively or destructively. Wave Interference Sound waves can be made to interfere con- structively or destructively as they reflect from a curved wall or a curved backdrop in a concert hall. Much planning and great expense goes into designing the acoustics in a fine perfor- mance hall. Seismic waves are produced by energy traveling through the material medium of Earth. Seismic waves are of three types—S, P, and L. S-waves (secondary waves) are trans- verse or shear, and cannot travel through fluids. For additional content background on this topic, go to the Glencoe Science Web site at science.glencoe.com. B a r r y L . R u n k / G r a n t H e i l m a n P h o t o g r a p h y , I n c . CHAPTER 1 Helping You Prepare O N 6F These seismic waves reflect off the fluid outer core of Earth. P-waves, or primary waves, are compressional, or longitudinal, waves. They may pass through all of Earth’s materials and are detected first. L-waves are seismic waves that occur along Earth’s surface. They cause up-down and rolling motions on the surface, which is why they are so destructive. The rainbow pattern seen on the back of compact disks is a diffrac- tion pattern that results from the grooves on the disk and the differ- ent wavelengths of visible light. CHAPTER 1 1 Waves Chapter Vocabulary wave mechanical wave transverse wave compressional wave electromagnetic wave amplitude wavelength frequency reflection refraction diffraction interference What do you think? Science Journal The filters shown are polarizing filters. These filters allow only light waves that vibrate in a specific direction to pass through them. Waves in ordinary light vibrate in all directions. O n a breezy day in Maui, Hawaii, windsurfers ride the ocean waves. What forces are operating on the windsurfer and his sailboard? The wind catches the sails and helps propel the sailboard, but other forces also are at work—waves. Waves carry energy. You can see the ocean waves in this picture, but there are many kinds of waves you cannot see. Microwaves heat your food, radio waves transmit the music you listen to into your home, and sound waves carry that music from the radio to your ears. In this chapter, you will learn about different types of waves and how they behave. What do you think? Science Journal What is this picture about? What causes the light and dark areas? Hint: Some sunglasses have this kind of lens. Write your answer or best guess in your Science Journal. 6 N O Waves 1 1 6 N O CHAPTER 1 Waves Energy Waves are periodic disturbances that carry energy. The larger the amplitude of the wave, the more energy is transferred. EXPLORE ACTIVITY Purpose Use the Explore Activity to give students an opportunity to observe and describe wave behavior. Logical-Mathematical Materials large, clear-plastic plate; small cork or piece of a soda straw; dropper; water Teaching Strategies • Suggest that students observe closely because the waves will move quickly. • Tell students to be sure the water is still before adding drops of water. They also should be careful not to dis- turb the water when adding the cork. Observe Circular waves travel outward from the point where the drops hit the water’s surface. Drops released from a height of 20 cm cause larger waves and transfer more energy than do drops released from a height of 10 cm. The cork bobs up and down as the waves pass but does not move horizontally. LS COOP LEARN ELL L2 7 I t’s a beautiful autumn day. You are sitting by a pond in a park. Music blares from a school marching band practicing for a big game. The music is carried by waves. A fish jumps, making a splash. Waves spread past a leaf that fell from a tree, causing the leaf to move. In the following activity, you’ll observe how waves carry energy that can cause objects to move. Observe wave behavior 1. Fill a large, clear plastic plate with 1 cm of water. 2. Use a dropper to release a single drop of water onto the water’s surface. Repeat. 3. Float a cork or straw on the water. 4. When the water is still, repeat step 2 from a height of 10 cm, then again from 20 cm. Observe In your Science Journal, record your observations and describe the movements of the floating object. EXPLORE ACTIVITY 7 O N 7 Handbook Reference Making a Concept Map Study Fold Make the follow- ing Foldable to organize infor- mation by diagramming ideas about waves. 1. Place a sheet of paper in front of you so the long side is at the top. Fold the bottom of the paper to the top, stopping about four centimeters from the top. 2. Draw an oval above the fold. Write Mechanical Waves inside the oval. 3. Fold the paper in half from the left side to the right side and then unfold. Through the top thickness of the paper, cut along the fold line to form two tabs. 4. Draw an oval on each tab. Write Transverse Waves in one oval and Compressional Waves in the other, as shown. Draw arrows from the large oval to the smaller ovals. 5. As you read the chapter, write information about the two types of mechanical waves under the tabs. FOLDABLES Reading & Study Skills FOLDABLES Reading &Study Skills CHAPTER 1 Waves O N 7 Dinah Zike Study Fold Purpose Have students make and use a Foldable concept map to list examples of and record information on two types of mechanical waves—transverse waves and compressional waves. After reading, students can use the Foldable as a study guide. For additional help, see Foldables Worksheet p. 15 in Chapter Resources Booklet, or go to the Glencoe Science Web site at science.glencoe.com. See After You Read in the Study Guide at the end of this chapter. FOLDABLES Reading & Study Skills FOLDABLES Reading &Study Skills Before You Read Before You Read Process Provide students with diagrams of transverse waves with different amplitudes. Ask them to identify which diagram shows waves generated by drop- ping water from a greater height. Use Performance Assessment in the Science Classroom, p. 89. Bellringer Transparency Display the Section Focus Transparency for Section 1. Use the accompanying Trans- parency Activity Master. ELL L2 S E C T I O N 1 1 PORTFOLIO Activity, p. 10 PERFORMANCE ASSESSMENT MiniLAB, p. 11 Skill Builder Activities, p. 12 See page 32 for more options. CONTENT ASSESSMENT Section, p. 12 Challenge, p. 12 Chapter, pp. 32–33 Section Planner What are waves? S E C T I O N What is a wave? When you are relaxing on an air mattress in a pool and someone does a cannonball off the diving board, you suddenly find yourself bobbing up and down. You can make something move by giving it a push or pull, but the person jumping didn’t touch your air mattress. How did the energy from the cannon- ball dive travel through the water and move your air mattress? The up-and-down motion was caused by the peaks and valleys of the ripples that moved from where the splash occurred. These peaks and valleys make up water waves. Waves Carry Energy Waves are rhythmic disturbances that carry energy without carrying matter, as shown in Figure 1A. You can see the energy of the wave from the speedboat traveling outward, but the water only moves up and down. If you’ve ever felt a clap of thunder, you know that sound waves can carry large amounts of energy. You also transfer energy when you throw something to a friend, as in Figure 1B. However, there is a difference between a moving ball and a moving wave. A ball is made of matter, and when it is thrown, the matter moves from one place to another. So, unlike the moving wave, throwing a ball involves the transport of matter as well as energy. I Explain the relationship among waves, energy, and matter. I Describe the difference between transverse waves and compres- sional waves. Vocabulary wave mechanical wave transverse wave compressional wave electromagnetic wave You can hear music and other sounds because of waves. Figure 1 The wave and the thrown ball carry energy. The waves created by a boat move mostly up and down, but the energy travels outward from the boat. When the ball is thrown, the ball, as well as the energy put into the throw, moves forward. 8 N O CHAPTER 1 Waves Waves Surfing may seemlike a fairly new sport, but it’s not. In fact, people think there were surfers in Hawaii in the 1400s. When Captain Cook landed in the Hawaiian Islands in 1778, he was greeted by an islander on a surfboard! Ride the wave! Section Focus Transparency 1 1 1. Name some different kinds of waves. 2. When waves travel through a medium, is any material moved along? Illustrate your answer with an example. 3. What type of waves do not require a mediumfor travel? 7 Chapter Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Tie to Prior Knowledge Ask students to describe any waves they know of. Discuss with them the form of energy transferred by each wave. What are waves? 8 N O CHAPTER 1 Waves Students might be surprised that some waves are described as mechanical. The word mechanical comes from the Latin word mechanicus, mean- ing “machine.” Based on this, have students discuss why mechanical is an appropriate term to use for waves. One defin- ition of machine is a device that trans- mits energy. In a mechanical wave, matter transmits energy. Linguistic LS L2 What is a wave? Discussion Ask students to describe how being near a source of deep, loud sounds, such as heavy machinery or the subwoofer of a stereo, demonstrates that waves carry energy. You can feel the vibra- tions as well as hear the sound. Auditory-Musical A Model for Waves Make a Model Have students duplicate the model described in the text. As they do this, emphasize that they are like the molecules of water through which a wave flows. Point out that the ball is made of matter, but i n the model it represents energy. Kinesthetic LS COOP LEARN ELL L1 LS L1 A Model for Waves How does a wave carry energy without transporting matter? Imagine a line of people, as shown in Figure 2A. The first person in line passes a ball to the second person, who passes the ball to the next person, and so on. Passing a ball down a line of people is a model for how waves can transport energy without transport- ing matter. Even though the ball has traveled, the people in line have not moved. In this model, you can think of the ball as repre- senting energy. What do the people in line represent? Think about the ripples on the surface of a pond. The energy carried by the ripples travels through the water. The water is made up of water molecules. It is the individual mol- ecules of water that pass the wave energy, just as the people in Figure 2A pass the ball. The water molecules transport the energy in a water wave by colliding with the molecules around them, as shown in Figure 2B. What is carried by waves? Mechanical Waves In the wave model, the ball could not be transferred if the line of people didn’t exist. The wave energy of a water wave could not be transferred if no water molecules existed. These types of waves, which use matter to transfer energy, are called mechanical waves. The matter through which a mechanical wave travels is called a medium. For ripples on a pond, the medium is the water. A mechanical wave travels as energy is transferred from par- ticle to particle in the medium. For example, a sound wave is a mechanical wave that can travel through air, as well as solids, liquids, and other gases. The sound wave travels through air by transferring energy from gas molecule to gas molecule. Without a medium such as air, you would not hear sounds. In outer space sound waves can’t travel because there is no air. SECTION 1 What are waves? O N 9 Figure 2 As the students pass the ball, the students’ positions do not change—only the position of the ball changes. The mol- ecules in water bump each other and pass the energy of a wave, even though they don’t travel with the wave. Mechanical Waves Section 1 What are waves? O N 9 Answer energy Reading Check Figure 2B Tell students that the water molecules near the surface of a wave actually travel in small circles. The boundary between air and water acts like a solid due to surface tension and pushes on the water molecules. This gives them a combination of transverse and compressional movement. Have students model this move- ment with a cork in water. Kinesthetic LS ELL L1 Chapter Resources Booklet Note-taking Worksheets, pp. 31–32 Transparency Activity, p. 42 Directed Reading for Content Mastery, pp. 17, 18 Resource Manager Transverse Waves In a mechanical transverse wave, the wave energy causes the matter in the medium to move up and down or back and forth at right angles to the direction the wave trav- els. You can make a model of a transverse wave. Stretch a long rope out on the ground. Hold one end in your hand. Now shake the end in your hand back and forth. By adjusting the way you shake the rope, you can create a wave that seems to slide along the rope. When you first started shaking the rope, it might have appeared that the rope itself was moving away from you. But it was only the wave that was moving away from your hand. The wave energy moves through the rope, but the matter in the rope doesn’t travel. You can see that the wave has peaks and valleys at regular intervals. As shown in Figure 3, the high points of trans- verse waves are called crests. The low points are called troughs. What are the highest points of transverse waves called? 10 N O CHAPTER 1 Waves Crest Trough Figure 3 The high points on the wave are called crests and the low points are called troughs. Figure 4 A compressional wave can travel through a coiled spring toy. As the wave motion begins, the coils near the string are close together and the other coils are far apart. The wave, seen in the squeezed and stretched coils, travels along the spring. The string and coils did not travel with the wave. Each coil moved only slightly forward and then back to its original position. Mechanical Waves, continued Use an Analogy Ask students to think of people “doing the wave” in a stadium. Point out that this wave is similar to a transverse mechanical wave because the people, like particles, move up and down at right angles to the direction the wave moves. Visual-Spatial Quick Demo Put a clear plate with colored water on an overhead projector. Ask students to predict what will happen to a floating object as waves are generated in the water. Generate waves either by dropping small objects into the water or by moving a finger in the water. The floating object will bob up and down because the water waves are very much like transverse waves. Visual-Spatial LS L3 LS L2 10 N O CHAPTER 1 Waves Answer crests Reading Check Activity Ask students to list on chart paper examples of mechanical waves. Have them draw each type of wave, describe each wave as transverse or compressional, and label the different parts of each wave. Visual-Spatial P LS COOP LEARN L2 There are three main types of seismic waves. Primary (P) waves oscillate back and forth along the direction the wave travels. Secondary (S) waves oscillate perpendicular to the direction of wave motion. Surface (L) waves cause horizontal and, some- times, vertical ground surface movement. Acti ve Readi ng Bubble Map Using a bubble map helps students start ideas flowing about a given topic. Words are clustered to describe a concept. Students can use the bubble map for a prewrite, to gener- ate ideas before writing in their Journals, or to review for a test. Have students design a Bubble Map for the different types of waves described in this section. Compressional Waves Mechanical waves can be either transverse or compressional. In a compressional wave, matter in the medium moves forward and backward in the same direc- tion that the wave travels. You can make a compressional wave by squeezing together and releasing several coils of a coiled spring toy, as shown in Figure 4. You see that the coils move only as the wave passes. They then return to their original position. So, like transverse waves, com- pressional waves carry only energy forward along the spring. In this example, the spring is the medium the wave moves through, but the spring does not move along with the wave. Sound Waves Sound waves are compressional waves. How do you make sound waves when you talk or sing? If you hold your fingers against your throat while you hum, you can feel vibra- tions. These vibrations are the movements of your vocal cords. If you touch a stereo speaker while it’s playing, you can feel it vibrat- ing, too. All waves are produced by something that is vibrating. Making Sound Waves How do vibrating vocal cords, strings, and other objects make sound waves? To find out, look at the drumhead stretched over the open end of the drum shown in Figure 5. When the drum- head moves upward, it touches some of the molecules that make up the air. When everything is quiet, these molecules are spaced about the same distance apart. However, when the drumhead moves upward, it pushes the molecules together. The group of molecules that are squeezed together is called a compression. When the drumhead moves downward, the molecules have more room and move away fromeach other. A place where mole- cules are far apart is called a rarefaction (rar uh FAK shun). These disturbed molecules then collide with the molecules next to them, transferring the energy they are carrying. This causes the compres- sionand therarefactiontomoveawayfromthe drumhead. SECTION 1 What are waves? O N 11 Comparing Sounds Procedure 1. Hold a wooden ruler firmly on the edge of your desk so that most of it extends off the edge of the desk. 2. Pluck the free end of the ruler so that it vibrates up and down. Use gentle motion at first, then pluck with more energy. 3. Repeat step 2, moving the ruler about 1 cm further onto the desk each time until only about 5 cm extend off the edge. Analysis 1. Compare the loudness of the sounds that are made using little energy with those made using more energy. 2. Describe the differences in the sound as the ruler was moved. Compression Rarefaction Compression Molecules that make up air Figure 5 A vibrating drumhead makes compressions and rarefactions in the air. How do your vocal cords make compressions and rarefac- tions in air? Making Sound Waves Section 1 What are waves? O N 11 Purpose Students compare and contrast various sounds made by a vibrating object. Auditory-Musical Materials wooden ruler Teaching Strategies Monitor students to ensure their results include information about the length of the ruler hanging over the table. Troubleshooting Make sure students do not pluck hard enough to break the ruler. Analysis 1. Using more energy produces louder sounds. 2. The greater the length of the vibrating object, the lower the pitch produced. LS ELL L2 Per formance Give students materials of different lengths and ask them to choose and make sounds with the ones that produce lower-pitched sounds. Use PASC, p. 97. Mini LAB Caption Answer Figure 5 The vocal cords vibrate, alter- nately squeezing air particles together and letting them spread apart. Hearing Impaired Some students may not be able to hear the sounds made by the ruler as they do the MiniLAB. Have these students pay atten- tion to feeling the vibrations. They should be able to feel the vibrations with the hand holding the ruler on the desk. Suggest they pluck the ruler several times while paying attention to what they feel. When they are familiar with the feeling, they can finish the lab. Compressional waves are often called longitudinal waves. Chapter Resources Booklet Transparency Activity, pp. 45–46 Enrichment, p. 28 Reinforcement, p. 25 MiniLAB, p. 3 Resource Manager Reteach Demonstrate compressional and transverse waves using a spring toy. Have students iden- tify each type of wave and the parts of the waves. Visual-Spatial Challenge Ask students to investigate the behavior of surface waves near the seashore and make posters showing what they find. As the waves approach land, water molecules near the surface experience more ellipti- cal movement, causing the waves to form high crests that eventually crash into land. Visual-Spatial LS L3 LS L2 12 N O CHAPTER 1 Waves Section Assessment 1. Describe the movement of a floating object on a pond when struck by a wave. 2. Why can’t a sound wave travel from a satellite to Earth? 3. Give one example of a transverse wave and one example of a compressional wave. How are they similar and different? 4. What is the difference between a mechani- cal wave and an electromagnetic wave? 5. Think Critically How is it possible for a sound wave to transmit energy but not matter? 6. Concept Mapping Create a concept map that shows the relationships among the following: waves, mechanical waves, electromagnetic waves, compressional waves, and transverse waves. For more help, refer to the Science Skill Handbook. 7. Using a Word Processor Use word-processing software to write short descriptions of the waves you encounter during a typical day. For more help, refer to the Technology Skill Handbook. Electromagnetic Waves When you listen to the radio, watch TV, or use a microwave oven to cook, you use a different kind of wave—one that doesn’t need matter as a medium. Waves that do not require matter to carry energy are called electromagnetic waves. Electromagnetic waves are transverse waves that are produced by the motion of electrically charged particles. Just like mechanical waves, electromagnetic waves can travel through a medium such as a solid, liquid, or gas. Radio waves are electromagnetic waves that travel through the air from a radio station, and then through the solid walls of your house to reach your radio. However, unlike mechanical waves, electro- magnetic waves can travel through outer space or through a vacuum where no matter exists. Useful Waves In space, which has no air or any other medium, orbiting satellites beam radio waves to TVs, radios, and cellular phones on Earth’s surface. However, radio waves are not the only electromagnetic waves traveling in space. You use sunscreen to protect yourself from ultraviolet rays. Infrared and ultraviolet waves travel from the Sun through space before they reach Earth’s atmosphere. Infrared waves feel warm when they strike your skin. Other useful electromagnetic waves include X rays and visible light. X rays are useful not only in medical applications, but also for security checks in airports as luggage is scanned. And without visible light you wouldn’t see color or be able to read this page. Maybe you’ve used a global positioning system (GPS) receiver to determine your location while driving, boating, or hiking. Earth- orbiting satellites send electromagnetic radio waves that transmit their exact locations and times of transmission. The GPS receiver uses information from four of these satellites to determine your location to within about 16 m. Electromagnetic Waves 12 N O CHAPTER 1 Waves Physics There are 24 GPS satellites, and they orbit Earth at a height of 17,500 km. Their electromagnetic radio waves can be received all over Earth, regardless of the weather. GPS was designed for and is operated by the U.S. Department of Defense and provides positioning information to military sub- marines, helicopters, ships, bombers, tanks, and missiles. However, since the signals can be received by an unlim- ited number of users, they are increasingly important in everyday civilian navigation. Process Have students draw dia- grams of transverse and com- pressional waves, labeling the crests and troughs. Use PASC, p. 127. Answers to Section Assessment 1. It bobs up and down. 2. It requires a medium through which to travel, and there is no medium in space. 3. Possible answer:Water waves are transverse waves. Sound waves are compressional waves. Compressional waves cause vibration in the direc- tion of wave movement.Transverse waves cause vibration at right angles to the wave’s direction. Both involve periodic motion and carry energy. 4. Mechanical waves use matter to transmit energy. Electromagnetic waves do not require matter to carry energy. 5. The wave causes molecules of matter to vibrate and bump neighbor molecules. 6. Answers should show mechanical waves as compressional or trans- verse; electromagnetic waves are transverse. 7. Answers might include radio waves, sound waves, or waves in a bathtub. Bellringer Transparency Display the Section Focus Transparency for Section 2. Use the accompanying Trans- parency Activity Master. ELL L2 S E C T I O N 2 2 SECTION 2 Wave Properties O N 13 Amplitude Can you describe a wave? One way might be to tell how high a water wave rises above, or falls below, the normal level. This distance is called the wave’s amplitude. The amplitude of a transverse wave is one-half the distance between a crest and a trough, as shown in Figure 6A. In a compressional wave, the amplitude is greater when the particles of the medium are squeezed closer together in each compression and spread farther apart in each rarefaction. Amplitude and Energy A wave’s amplitude is related to the energy that the wave carries. For example, the electromagnetic waves that make up bright light have greater amplitudes than the waves that make up dim light. Waves of bright light carry more energy than the waves that make up dim light. In a similar way, loud sound waves have greater amplitudes than soft sound waves. Loud sounds carry more energy than soft sounds. If a sound is loud enough, it can carry enough energy to damage your hearing. As you can see in Figure 6B, when a hurricane strikes a coastal area, the resulting water waves can damage anything that stands in their path. The waves caused by a hurricane carry more energy than the small waves or ripples on a pond. I Describe the relationship between the frequency and wavelength of a wave. I Explain why waves travel at different speeds. Vocabulary amplitude wavelength frequency The energy carried by a wave depends on its amplitude. Wave Properties S E C T I O N Amplitude Amplitude Figure 6 A transverse wave has an amplitude. The amplitude is a measure of how high the crests are or how deep the troughs are. A wave of large amplitude is responsible for this damage. PORTFOLIO Extension, p. 14 Science Journal, p. 16 PERFORMANCE ASSESSMENT Skill Builder Activities, p. 17 See page 32 for more options. CONTENT ASSESSMENT Section, p. 17 Challenge, p. 17 Chapter, pp. 32–33 Section Planner Section 2 Wave Properties O N 13 Tie to Prior Knowledge Ask students whether it takes more or less energy to twirl a jump rope high enough to clear a short person or a tall person. tall Explain that in this section, they will learn how to describe the energy different waves carry. Waves Visible light and ultraviolet (UV) radiation both come from the Sun. UV radiation causes eye damage, skin cancer, and burns skin. Visible light and UV radiation are the same type of wave; the difference between the two is their wavelengths. The Sun’s Radiant Energies Section Focus Transparency 2 2 1. How are visible light and UV radiation the same? 2. How can you protect yourself fromthe harmful consequences of UV radiation? 7 Chapter Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Wave Properties Chapter Resources Booklet Transparency Activity, p. 43 Directed Reading for Content Mastery, p. 19 Resource Manager The devastating effect that a wave with large amplitude can have is seen in the aftermath of tsunamis. Tsunamis are huge sea waves that are caused by underwater earthquakes along faults on the seafloor. The movement of the seafloor along the fault produces the wave. As the wave moves toward shallow water and slows down, the amplitude of the wave grows. The tremendous amounts of energy tsunamis carry cause great damage when they move ashore. Wavelength Another way to describe a wave is by its wavelength. For a transverse wave, wavelength is the distance from the top of one crest to the top of the next crest, or from the bottom of one trough to the bottom of the next trough, as shown in Figure 7A. For a compressional wave, the wavelength is the distance between the center of one compression and the center of the next com- pression, or from the center of one rarefaction to the center of the next rarefaction, as shown in Figure 7B. Wavelength is an important characteristic of a wave. For example, the difference between red light and green light is that they have different wavelengths. The wavelength of red light is longer than the wave- length of green light. It is the wavelength of visible light that determines its color. Some electromagnetic waves, like X rays, have extremely short wavelengths. Others, like microwaves, have longer wavelengths. The range of wavelengths of electromagnetic waves is shown in Figure 8. 14 N O CHAPTER 1 Waves Wavelength Wavelength Wavelength Wavelength Compression Rarefaction Piston D e c r e a s i n g w a v e l e n g t h Visible light AM radio Shortwave radio Radio waves FM radio Television Radar Microwaves Infrared Ultraviolet X rays Gamma rays Figure 8 The wavelengths and frequencies of electromagnetic waves vary. Figure 7 Wavelength is measured differently for transverse and compressional waves. For compressional waves, measure from compression to compression or from rarefaction to rarefaction For transverse waves, measure crest to crest or trough to trough. Activity Ask students to bring in maga- zine and newspaper articles about tidal waves (tsunamis) and earthquakes around the world. Display the articles and discuss with students the relationship between energy, wave amplitude, and the amount of destruction caused. Interpersonal Wavelength Extension Explain that both compres- sional and transverse waves are commonly graphed as sine waves with amplitude on the vertical axis and wavelength on the horizontal axis. Have students prepare this type of graph for both waves shown in Figure 7. The graph of the transverse wave should closely resemble the wave on the oscilloscope in Figure 7A. On the graph of the compressional wave, the height of the graphed wave should reflect the intensity of the compression, while the wavelength should represent the distance between compressions and rarefactions. Visual-Spatial P LS L3 LS L2 14 N O CHAPTER 1 Waves Tsunamis can travel thousands of kilometers, in all directions, at speeds of more than 700 km/h. When a tsunami approaches a coastline, the water piles up and forms a wave crest that can tower 30 m high or higher. The threshold of human hearing for sound intensity (loudness) is 0 dB (10 –12 watts Ϭ m 2 ). Hearing damage commences at sustained levels of about 85 dB. Normal conversation has an intensity of about 60 dB. A jet engine can generate noise levels of about 120 dB to 140 dB. Figure 8 This figure shows that shorter wave- length implies higher frequency. We also know that electromagnetic waves are made of particles called photons. Waves with a longer wavelength have lower energy per photon than waves with a shorter wavelength. The amplitude of the waves depends on the energy per unit area (i.e., the number of photons per unit area), not the energy per photon. Amplitude Frequency The frequency of a wave is the number of wavelengths that pass a given point in 1s. The unit of frequency is the number of wavelengths per second, or hertz (Hz). Recall that waves are produced by something that vibrates. The faster the vibration is, the higher the frequency is of the wave that is produced. How is the frequency of a wave measured? A Sidewalk Model For waves that travel with the same speed, frequency and wavelength are related. To model this relationship, imagine people on two parallel moving sidewalks in an airport, as shown in Figure 9. One sidewalk has four trav- elers spaced 4 m apart. The other sidewalk has 16 travelers spaced 1 m apart. Now imagine that both sidewalks are moving at the same speed and approaching a pillar between them. On which side- walk will more people go past the pillar? On the sidewalk with the shorter distance between people, four people will pass the pillar for each one person on the other sidewalk. When four people pass the pillar on the first sidewalk, 16 people pass the pillar on the second sidewalk. SECTION 2 Wave Properties O N 15 4 m 4 m 4 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m 1 m Figure 9 This moving sidewalk illustration shows how wavelength and frequency are related. Frequency Use Science Words Word Origin Have students inves- tigate the origin of the word hertz and why it is used to describe frequency. The unit hertz was named after Heinrich Hertz, a Ger- man physicist who studied electromag- netic waves. Linguistic LS L2 Section 2 Wave Properties O N 15 Answer in wavelengths per second Reading Check Extension Many animals communicate using sounds that are inaudible to humans. Have students research animals that do this and prepare reports about the frequencies at which the animals make sounds. Possible animals to study include whales and dolphins, which use ultrasonic frequencies, and elephants and hippos, which use infra- sonic frequencies. Linguistic Discussion How does pressing a string on a guitar affect the frequency of the sound produced? It short- ens the stri ng, whi ch i ncreases the f requenc y of the sound the stri ng produces when it is plucked. How does this relate to the sounds produced by a harp? On a harp, the shor t stri ngs produce hi gh fre- quency sounds and the long strings produce l ow frequency sounds. Auditory-Musical LS L2 LS L3 Music Have students find out what quarter tones are and play recordings of music with quarter tones for the class. The difference in frequency between two adjacent pitches in some types of music, including Hindu music, is about half that between adjacent pitches in western music. These pitches are called quarter tones. Auditory-Musical LS ELL L3 Chapter Resources Booklet Enrichment, p. 29 Home and Community Involvement, p. 42 Reading and Writing Skill Activities, p. 33 Resource Manager Frequency, continued Activity Have each student fill a bowl with water and dip a pencil into and out of the water to form waves. They should notice that dipping the pencil with low frequency produces waves with longer wavelengths (greater distance between crests) than dipping the pencil with high frequency. Have students use a stopwatch to help calibrate the frequencies of their waves. Kinesthetic LS ELL L1 16 N O CHAPTER 1 Waves Musical Instruments Ask students to investigate various musical instruments and write in their Science Journals what vibrates on each instrument to make sound and how this produces certain pitches. Students might mention the reed of a clar- inet or the lips of a trumpet player. Air inside the instrument also vibrates. The shape and material of the instrument affect pitch. Linguistic P LS L3 The wavelengths are much shorter that those of the soundwaves we hear. Chapter Resources Booklet Reinforcement, p. 26 Cultural Diversity, p. 61 Resource Manager Quick Demo Have students who play instruments demonstrate com- pressional waves of high and low frequency by producing notes of varying pitch. If an oscilloscope is available, connect it to a transducer (microphone) to show students the wavelengths and amplitudes of the notes. Auditory-Musical LS ELL L2 16 N O CHAPTER 1 Waves C B A G F E D C C C D E F G A B Frequency (Hz) 550 500 450 400 350 300 250 200 C B A G F E D C C C D E F G A B Wavelength (cm) 130 120 110 100 90 80 70 60 Frequency and Wavelength Suppose that each person in Figure 9 represents the crest of a wave. Then the movement of people on the first sidewalk is like a wave with a wavelength of 4 m. For the second sidewalk, the wavelength would be 1 m. On the first sidewalk, where the wavelength is longer, the people pass the pillar less frequently. Longer wavelengths result in smaller frequencies. The people pass the pillar more frequently on the second sidewalk, where the wavelength is shorter. Larger frequencies result in shorter wavelengths. This is true for all waves that travel at the same speed. As the frequency of a wave increases, its wavelength decreases. Color and Pitch Because frequency and wavelength are related, either the wavelength or frequency of a light wave deter- mines the color of the light. For example, blue light has a larger frequency and shorter wavelength then red light. In a sound wave, either the wavelength or frequency deter- mines the pitch. Pitch is the highness or lowness of a sound. A flute makes musical notes with a high pitch and produces sounds of high frequency. A tuba produces notes with a low pitch and a low frequency. When you sing a musical scale, the pitch and frequency increase from note to note. Wavelength and frequency are also related for sound waves. As the frequency of sound waves increase, their wavelength decreases. Figure 10 shows how the frequency and wavelength change for notes on the musical scale. Figure 10 The frequency of the notes on a musical scale increases as the notes get higher in pitch, but the wavelength of the notes decreases. Sound waves with ultra- high frequencies cannot be heard by the human ear, but are used by medical professionals in several ways. They perform echocardiograms of the heart, produce ultrasound images of internal organs, break up blockages in arteries and kill bacteria and sterilize surgical instruments. How do the wavelengths of these sound waves compare to sound waves you can hear? Section 2 Wave Properties O N 17 Wave Speed Reteach Have students use a spiral drawing toy to demonstrate the amplitude, wavelength, and fre- quency of a wave. Kinesthetic Challenge Compare the sound of a siren moving toward you with the sound of a siren moving away from you. When the siren is moving toward you, the wavelengths of the compressi onal waves decrease, resulting in higher pitches. As the siren moves away from you, the wavelengths increase and the pitches get lower. This is known as the Doppler effect. Logical-Mathematical LS L3 LS L1 Wave Speed You’ve probably watched a distant thunderstorm approach on a hot summer day. You see a bolt of lightning flash between a dark cloud and the ground. Do the sound waves, or thunder, pro- duced by the lightning bolt reach your ears at the same instant you see the lightning? If the thunderstorm is many kilometers away, several seconds will pass between when you see the light- ning and when you hear the thunder. This happens because light travels much faster in air than sound does. Light is an electro- magnetic wave that travels through air at about 300 million m/s. On the other hand, sound is a mechanical wave that travels through air at about 340 m/s. Mechanical waves such as sound travel faster in a medium in which the atoms that make up the medium are closer together. Sound travels faster in solids than in liquids and faster in liquids than in gases. This is because atoms are closer to each other in a solid than in a liquid, and closer together in a liquid than in a gas. Electromagnetic waves such as light behave differently than mechanical waves. Unlike mechanical waves, they travel faster in gases than in solids or liquids. You know that you can get to your next class faster if the hallways are nearly empty than if they are filled with other students. Electromagnetic waves behave the same way. If many atoms are in the medium, electromagnetic waves are slowed down. For example, the speed of light is one and a half times faster in air than it is in glass. SECTION 2 Wave Properties O N 17 Section Assessment 1. How does the frequency of a wave change as its wavelength changes? 2. Why is a sound wave with a large ampli- tude more likely to damage your hearing than one with a small amplitude? 3. What accounts for the time difference in seeing and hearing a fireworks display? 4. Why is the statement “The speed of light is 300 million m/s” not always correct? 5. Think Critically Explain the differences between the waves that make up bright, green light and dim, red light. 6. Predicting A biologist studying bison puts her ear next to the ground. By doing this she knows that the herd is coming toward her. Explain. For more help, refer to the Science Skill Handbook. 7. Solving One-Step Equations The product of the wavelength and the frequency of a wave is the speed of the wave. If a sound wave traveling through water has a speed of 1,470 m/s and a frequency of 2,340 Hz, what is its wavelength? For more help, refer to the Math Skill Handbook. Research Visit the Glencoe Science Web site at science.glencoe.comfor information about wave speed in different materials. Make a graph to show the differences. Answers to Section Assessment 1. The frequency increases as the wave- length decreases. 2. Waves having large amplitudes carry more energy than waves with small amplitudes. 3. Light travels much faster than sound. 4. The speed of light varies, depending on the medium through which it travels.The speed of light is 300 million m/s in air. 5. The waves that make up bright green light have shorter wave- lengths, higher frequencies, and larger amplitudes. 6. The biologist can hear the vibrations in the ground caused by the moving herd. 7. wavelength ϭwave speed Ϭwave frequency ϭ1,470 m/s Ϭ2,340 Hz ϭ0.628 m Process Fill test tubes with dif- ferent amounts of water and tap on them gently with a glass stir- ring rod. Have students explain the differences between the pitches produced. The more water in a tube, the shorter the wavelength of air that fits in the tube, so the higher the pitch produced when the glass is tapped. Use PASC, p. 89. Internet Addresses Explore the Glencoe Science Web site at science.glencoe.com to find out more about topics in this section. Write a summary paragraph of how this activity demonstrated any of the vocabulary words from the first two sections of the chapter. For more help, refer to the Science Skill Handbook. Waves on a Spring 18 N O CHAPTER 1 Waves 3. Stretch the springs between two people to the length suggested by your teacher. Measure the length. 4. Create a wave with a quick, sideways snap of the wrist. Time several waves as they travel the length of the spring. Record the average time in your data table. 5. Repeat step 4 using waves that have slightly larger amplitudes. 6. Squeeze together about 20 of the coils. Observe what happens to the unsqueezed coils. Release the coils and observe. 7. Quickly push the spring toward your partner, then pull it back. 8. Tie the yarn to a coil near the middle of the spring. Repeat step 7, observing the string. Conclude and Apply 1. Classify the wave pulses you created in each step as compressional or transverse. 2. Calculate and compare the speeds of the waves in steps 4 and 5. 3. Classify the unsqueezed coils in step 6 as a compression or a rarefaction. 4. Compare and contrast the motion of the yarn with the motion of the wave. W aves are rhythmic disturbances that carry energy through matter or space. Studying waves can help you understand how the Sun’s energy reaches Earth and sounds travel through the air. What You’ll Investigate What are some of the properties of transverse and compressional waves on a coiled spring? Materials long, coiled spring toy colored yarn (5 cm) meterstick stopwatch Goals I Create transverse and compressional waves on a coiled spring toy. I Investigate wave properties such as speed and amplitude. Safety Precautions WARNING: Avoid overstretching or tangling the spring to prevent injury or damage. Procedure 1. Prepare a data table such as the one shown. 2. Work in pairs or groups and clear a place on an uncarpeted floor about 6 mϫ2 m. Length of stretched spring toy 4.20 m Average time for a wave to travel from end to end—step 4 1.35 s Average time for a wave to travel from end to end—step 5 1.25 s Wave Data Purpose Students make waves with a coiled-spring toy and observe the waves. Kinesthetic Process Ski l l s observing and inferring, comparing and con- trasting, interpreting data, clas- sifying, making and using tables Time Required 45 minutes Safety Precautions Space student groups far enough apart that the coiled springs do not interfere with each other. Teaching Strategies • Help students compare the two types of waves they generate. • Help students recognize the parts of a wave. Troubleshooting Watch students to ensure that they do not tangle or overstretch the coiled springs. Answers to Questions 1. In steps 4 and 5, transverse waves were produced. In steps 6 to 7, com- pressional waves were produced. In step 8, a transverse wave was produced in the string. 2. Check students’ work. 3. rarefaction 4. A transverse wave formed in the string. A compression wave formed in the coiled spring toy. LS COOP LEARN ELL L2 Have students use a computer graphics program to create a display explaining the results of the activity. Process Have students draw and label the parts of each type of wave they generated in the activity. Use PASC, p. 127. Chapter Resources Booklet Lab Activity, pp. 9–11 Activity Worksheet, pp. 5–6 Resource Manager 18 N O CHAPTER 1 Waves Bellringer Transparency Display the Section Focus Transparency for Section 3. Use the accompanying Trans- parency Activity Master. ELL L2 S E C T I O N 3 3 SECTION 3 Wave Behavior O N 19 Reflection What causes the echo when you yell across an empty gymna- sium or down a long, empty hallway? Why can you see your face when you look in a mirror? The echo of your voice and the face you see in the mirror are caused by wave reflection. Reflection occurs when a wave strikes an object or surface and bounces off. An echo is reflected sound. Sound reflects from all surfaces. Your echo bounces off the walls, floor, ceiling, furniture, and people. You see your face in a mirror or a still pond, as shown in Figure 11A, because of reflection. Light waves produced by a source of light such as the Sun or a lightbulb bounce off your face, strike the mirror, and reflect back to your eyes. A mirror is smooth and even, therefore you see a clearly reflected image. However, when light reflects from an uneven or rough surface, you can’t see an image because the reflected light scatters in many different directions, as shown in Figure 11B. What causes reflection? I Explain how waves can reflect from some surfaces. I Explain how waves change direc- tion when they move from one material into another. I Describe how waves are able to bend around barriers. Vocabulary reflection refraction diffraction interference The reflection of waves enables you to see objects around you. Wave Behavior S E C T I O N Figure 11 The image formed by reflection depends on the smoothness of the surface. The smooth surface of a still pond allows light to reflect back to you so you can see your image. The rough, uneven surface of the same pond causes the light to reflect in many directions so that no sharp image is visible. PORTFOLIO Challenge, p. 25 PERFORMANCE ASSESSMENT Try at Home MiniLAB, p. 20 Skill Builder Activities, p. 25 See page 32 for more options. CONTENT ASSESSMENT Section, p. 25 Challenge, p. 25 Chapter, pp. 32–33 Section Planner Section 3 Wave Behavior O N 19 Wave Behavior Tie to Prior Knowledge Remind students that visible light rays are electromagnetic waves. Discuss whether they can see themselves in a mirror with- out light rays. Explain that in this section, they will learn how waves reflect and refract. Waves Artists work with all kinds of materials, so why not water? This image was made by placing an obstacle in the water and generating waves. As waves reach the obstacle, they move through the holes. Wave Art Section Focus Transparency 3 3 1. Describe what is happening in this picture. 2. What would happen to the wave pattern if both holes were plugged? 3. Do you think sound waves diffract in a similar fashion? Give an example that illustrates your answer. 7 Chapter Copyright © Glencoe/M cGra w-Hill,a division of the M cGra w-Hill Com panies, Inc. Reflection Refraction You’ve already seen that a wave changes direction when it reflects from a surface. Waves also can change direction in another way. Perhaps you have tried to grab a sinking object when you are in a swimming pool, only to come up empty- handed. Yet you were sure you grabbed right where you saw the object. This happens because the light rays from the object change direction as they pass from the water into the air. The bending of a wave as it moves from one medium into another is called refraction. Refraction and Wave Speed Remember that the speed of a wave can be different in different materials. For example, light waves travel faster in air than in water. Refraction occurs when the speed of a wave changes as it passes from one substance to another, as shown in Figure 12. A line that is perpendicular to the water’s surface is called the normal. When a light ray passes from air into water, it slows down and bends toward the normal. When the ray passes from water into air, it speeds up and bends away from the normal. The larger the change in speed of the light wave is, the larger the change in direction is. You notice refraction when you look down into a fishbowl. Refraction makes the fish appear to be closer to the surface but farther away from you than it is, as shown in Figure 13. Light rays reflected from the fish are bent away from the normal as they pass from water to air. Your brain interprets the light that enters your eyes by assuming that light rays always travel in straight lines. As a result, the light rays seem to be coming from a fish that is in a different location. 20 N O CHAPTER 1 Waves Observing How Light Refracts Procedure 1. Fill a large, opaque drinking glass or cup with water. 2. Place a white soda straw in the water at an angle. 3. Looking directly down into the cup from above, observe the straw where it meets the water. 4. Placing yourself so that the straw angles to your left or right, slowly back away about 1 m. Observe the straw as it appears above, at, and below the surface of the water. Analysis 1. Describe the straw’s appear- ance from above. 2. Compare the straw’s appearance above and below the water’s surface in step 4. Draw a diagram and explain the apparent effect. Air Water Normal Normal Figure 12 A wave is refracted when it changes speed. As the light ray passes from air to water, it refracts toward the normal. As the light ray passes from water to air, it refracts away from the normal. Refraction Quick Demo Demonstrate that different colors of white light refract at different angles by shining an intense beam of white light through a prism in a darkened room. Visual-Spatial LS ELL L2 20 N O CHAPTER 1 Waves Answer the bouncing of a wave off an object Reading Check An Advanced Warni ng System The Chinese used pottery jars to detect the sounds of an advancing enemy. Leather membranes were stretched over the mouths of empty 80-L pottery jars. The jars were lowered into deep shafts that were dug a few paces apart around the city, and men with good hearing were sta- tioned nearby. Not only could they hear the sounds of an approaching army, but by listening to different sounds from the shafts, the watchers also could judge from which direction the enemy was coming and how far away the enemy was. Why do you think the jars were put in shafts deep underground? The thudding footsteps of the approaching army produced low-frequency, long- wavelength vibrations in the ground. The shafts had to be deep enough to receive those sound vibrations and amplify them. Logical-Mathematical LS L3 T R Y AT HO M E Purpose Students observe how light refracts. Visual-Spatial Materials white soda straw, opaque drinking glass or cup; water Teaching Strategy The larger the diameter of the glass or cup, the easier it will be to see the refraction. Also, tell stu- dents to fill the glass or cup almost to the top. Analysis 1. The straw appears to be straight. 2. The straw appears to bend at the water’s surface. Light reflects from the straw and refracts as it passes from the water into the air.The speed of the light waves is also reduced in water. LS ELL L1 Performance Have students draw ray diagrams in their Science Journals that show how the light waves refract. Use PASC, p. 127. Mini LAB Section 3 Wave Behavior O N 21 Water droplet Sunlight Incident ray Color from Refraction Refraction causes prisms to separate sunlight into many colors and produces rainbows too. Figure 14 illustrates how refraction and reflection produce a rainbow when light waves from the Sun pass into and out of water droplets in the air. What produces a rainbow? Diffraction Why can you hear music from the band room when you are down the hall? You can hear the music because the sound waves bend as they pass through an open doorway. This bending isn’t caused by refraction. Remember that refraction occurs when waves change speed, but sound waves have the same speed in the band room and in the hallway. Instead the bending is caused by diffraction. Diffraction is the bending of waves around a barrier. Diffraction of Light Waves Can light waves diffract, too? You can hear your friends in the band room but you can’t see them until you reach the open door. Therefore, you know the light waves do not diffract as much as sound waves do. Are light waves able to diffract at all? Light waves do bend around the edges of an open door. However, for an opening as wide as a door, the amount the light bends is extremely small. As a result, the diffraction of light is far too small to allow you to see around a corner. Figure 13 When you look at the goldfish in the water, the fish is in a dif- ferent position than it appears. Normal SECTION 3 Wave Behavior O N 21 Figure 14 Light rays refract as they enter and leave each water drop. Each color refracts at different angles because of their different wave- lengths, so they separate into the colors of the spectrum. Answer Sunlight refracts as it enters raindrops, reflects from the far inside surfaces of the drops, and refracts as it leaves the drops. Reading Check Figure 14 When you look at a rainbow, you see an arc of col- ors. The refraction of light from water drops actually produces a circle of light, but we can only see the top of the circle because the ground blocks out the lower part. Red is at the top because, as you see in the sketch of the raindrop, red is bent less. Violet is at the bottom because it is bent more. Have students draw sketches to show how the reflec- tions create a circle with red on the outside. Visual-Spatial Diffraction Quick Demo Tell each student to straighten the first two fingers of one hand, spreading the fingers slightly to make a small slit between them. Then have stu- dents view a bright light through the slit. They will see fringes, or black lines, between their fingers as a result of dif- fraction. Kinesthetic LS ELL L1 LS ELL L1 The speed of light in a material depends on the characteristics of the material and the frequency of the incident light. High- frequency, short-wavelength light, such as violet light, travels more slowly in a material than lower-frequency, longer-wavelength light, such as red light. This means the vio- let light bends more than the red light as it moves from a vacuum (or air) to a denser medium. Chapter Resources Booklet Transparency Activity, p. 44 Enrichment, p. 30 MiniLAB, p. 4 Resource Manager 22 N O CHAPTER 1 Waves 22 N O CHAPTER 1 Waves Figure 15 Water waves bend or diffract around these islands. More diffraction occurs when the object is closer in size to the wavelength. Diffraction and Wavelength The reason that light waves don’t diffract much when they pass through an open door is that the wavelengths of visible light are much smaller than the width of the door. Light waves have wavelengths between 400 and 700 billionths of a meter, while the width of doorway is about one meter. Sound waves that you can hear have much longer wave- lengths. They bend more easily around the corners of an open door. A wave is diffracted more when its wavelength is similar in size to the barrier or opening. Diffraction of Water Waves Perhaps you have noticed water waves bending around barriers. For example, when water waves strike obstacles such as the islands shown in Figure 15, they don’t stop moving. Here the size and spacing of the islands is not too different from the wavelength of the water waves. So the water waves bend around the islands, and keep on moving. They also spread out after they pass through openings between the islands. If the islands were much larger than the water wave- length, less diffraction would occur. What happens when waves meet? Suppose you throw two pebbles into a still pond. Ripples spread from the impact of each pebble and travel toward each other. What happens when two of these ripples meet? Do they collide like billiard balls and change direction? Waves behave differently from billiard balls when they meet. In fact, after they pass, waves continue moving as though the other waves never existed. What happens when waves meet? Quick Demo Help students understand how to graph the addition of waves by demonstrating it on an overhead projector. Overlap transparencies of drawings of waves as you add them together. Visual-Spatial Discussion Have students consider what happens when three waves over- lap. If three waves interfere at a given point and have ampli- tudes of ϩ3 units, ϩ2 units, and Ϫ5 units, what is the amplitude of the resultant wave at that point? 0 units Logical-Mathematical LS L2 LS L2 LAB DEMONSTRATION LAB DEMONSTRATION Purpose to observe wave behavior Materials 2 pencils; paper; large, rectangu- lar glass baking dish; water Preparation Fill the dish with water to a depth of 2 cm. Use several books on each side to suspend the pan over a sheet of white paper. Place a strong light about 40 cm above the pan. Dim all other lights. Procedure To form waves, vibrate a vertical pencil up and down on one side of the pan. Show interference by vibrating two vertical pencils, about 10 cm apart, up and down at one end of the pan. Place an object in the path of the waves to show diffraction. Expected Outcome Students observe reflec- tion, diffraction, and interference. What would the waves have looked like if you had held the pencil horizontally instead of vertically when vibrating it? They would have formed a line of waves instead of circles. Students may think that as waves move from one medium to another and are refracted, the wavelength and frequency of the waves change. However, only the speed and direction of the waves change. Wave Interference When two waves overlap a new wave is formed by adding the two waves together. The ability of two waves to combine and form a new wave when they overlap is called interference. After they overlap, the individual waves con- tinue to travel on in their original form. The different ways waves can interfere are shown in Figure 16 on the next page. Sometimes when the waves meet, the crest of one wave overlaps the crest of another wave. This is called constructive interference. The amplitudes of these com- bining waves add together to make a larger wave while they over- lap. Destructive interference occurs when the crest of one wave overlaps the trough of another wave. In destructive interference, the amplitudes of the two waves combine to make a wave with a smaller amplitude. If the two waves have equal amplitudes and meet crest to trough, they cancel each other during the overlap. Waves and Particles Like waves of water, when light travels through a small opening, such as a narrow slit, the light spreads out in all directions on the other side of the slit. If small parti- cles, instead of waves, were sent through the slit, they would continue in a straight line without spreading. The spreading, or diffraction, is only a property of waves. Interference also doesn’t occur with particles. If waves meet, they reinforce or cancel each other, then travel on. If particles approach each other, they either collide and scatter or miss each other completely. Interfer- ence, like diffraction, is a property of waves, not particles. Y our brother is vacuuming and you can’t hear the television. Is it possible to diminish the sound of the vacuum so you can hear the TV? Can you eliminate unpleasant sounds and keep the sounds you do want to hear? Identifying the Problem It is possible to create a frequency that will destructively interfere with the sound of the vacuum and not the television. The graph shows the waves created by the vacuum and the television. Can you create destructive interference? Solving the Problem 1. Can you create the graph of a wave that will eliminate the noise from the vacuum but not the television? 2. Can you create the graph of a wave that would amplify the sound of the television? Problem-Solving Activity SECTION 3 Wave Behavior O N 23 Research Visit the Glencoe Science Web site at science.glencoe.comfor more information about wave interference. a b Noise from vacuum Noise from television Extension Explain to students that when an incident wave (one moving toward an object) and a reflected wave (one bounced off an object) meet, they sometimes form a standing, or stationary, wave. Because of the interfer- ence pattern, the standing wave doesn’t appear to be traveling. You can demonstrate a standing wave using a rope. Tie one end of the rope firmly to a doorknob or a laboratory table. Shake the other end to produce various standing wave patterns. Visual-Spatial Discussion How does interference affect the way music sounds in different concert halls? Con- structive and destructive interference patterns in a concert hall determine whether sound waves produced by indi- vidual voices or instruments combine to form waves that are pleasant or displeas- ing to listeners’ ears. Logical-Mathematical LS L3 LS L3 Section 3 Wave Behavior O N 23 Internet Addresses Explore the Glencoe Science Web site at science.glencoe.com to find out more about topics in this section. Chapter Resources Booklet Directed Reading for Content Mastery, pp. 19, 20 Mathematics Skill Activities, p. 47 Resource Manager National Math Standards Correlation to Mathematics Objectives 2, 5, 6, 8–10 Answers 1. The wave must be the opposite of the vacuum wave.That is, it must trough when the vacuum wave crests, and vice versa. 2. Any wave that crests and troughs in the same place will amplify the wave. Visualizing Interference Have students examine the pic- tures and read the captions. Then ask the following questions. Two waves both with an amplitude of 2 m pass through each other. The maximum amplitude reached is 4 m. Is this constructive or destruc- tive interference? constructive Two waves both with an amplitude of 2 m approach each other and the peak of the crest of one wave passes through the bottom of the trough of the other wave. What is the amplitude of the resulting wave at that instant? zero Visual-Spatial Activity Have two students hold the ends of a long rope. Ask stu- dents to practice making waves with the rope by moving their hands vertically or horizontally in quick strokes. The students should then work together to set up constructive and destructive interference with the waves in their ropes. Kinesthetic Extension Challenge students to find out how radio waves are used in radar and how stealth airplanes are built to evade detection by radar. Have students work in pairs to make posters showing the airplane profiles used and the materials used to enable these planes to avoid detection. LS L3 LS L2 24 N O CHAPTER 1 Destructive Interference W hether they are ripples on a pond or huge ocean swells, when water waves meet they can combine to form new waves in a process called interference. As shown below, wave interference can be constructive or destructive. A B Figure 16 VISUALIZING INTERFERENCE The two waves form a larger wave where the crests of both waves overlap. If the two waves have equal amplitude, they momentarily cancel when they meet. In constructive interference, a wave with greater amplitude is formed. A B A B In destructive interference, a wave with a smaller amplitude is formed. The original waves pass through each other and go on as they started. The crest of one wave approaches the trough of another. B A Constructive Interference The crests of two waves—A and B—approach each other. The original waves pass through each other and go on as they started. 24 N O CHAPTER 1 Waves Chapter Resources Booklet Lab Activity, pp. 13–14 Reinforcement, p. 27 Resource Manager Section 3 Wave Behavior O N 25 Reteach Divide the class in half and conduct a baseball game review with words from this chapter. Players match words with mean- ings and are out when they miss a word. Each team has three outs before the turn shifts to the other team. Interpersonal Challenge Have pairs of students prepare posters showing the types of waves produced by a combina- tion of (1) two transverse waves in which crests overlap, (2) two transverse waves in which crests and troughs overlap, (3) two compressional waves in which crests overlap, and (4) two com- pressional waves in which crests and troughs overlap. Visual-Spatial P LS COOP LEARN L3 LS COOP LEARN L2 Using Interference You might have seen someone use a power lawn mower or a chain saw. In the past, many people who performed these tasks damaged their hearing because of the loud noises produced by these machines. Today, specially designed ear protectors absorb the sound from lawn mowers and chain saws. The ear protectors lower the amplitudes of the harmful waves. The waves that reach the ears have smaller amplitudes and won’t damage eardrums. Reducing Noise Pilots and passengers of small planes have a more complicated problem. They can’t use ear protectors to shut out all the noise of the plane’s motor. If they did, the pilots wouldn’t be able to hear instructions from air-traffic controllers, and the passengers wouldn’t be able to hear each other talk. To solve this problem, engineers invented special devices that contain electronic cir- cuits as shown in Figure 17. These circuits detect the vibrations from the aircraft that make noise and produce sound frequen- cies that destructively interfere with those vibrations. However, the sound frequencies produced do not interfere with human voices, so people can hear and understand normal conversation. In these examples, destructive interference can be a benefit. SECTION 3 Wave Behavior O N 25 Section Assessment 1. Why don’t you see your reflection in a building made of rough, white stone? 2. If you’re standing on one side of a building, how are you able to hear the siren of an ambulance on the other side? 3. What behavior of light enables magnifying glasses and contact lenses to bend light rays and help people see more clearly? 4. What is diffraction? How does the amount of diffraction depend on wavelength? 5. Think Critically Why don’t light rays that stream through an open window into a darkened room spread evenly through the entire room? 6. Comparing and Contrasting When light rays pass from water into a certain type of glass, the rays refract toward the normal. Compare and contrast the speed of light in water and in the glass. For more help, refer to the Science Skill Handbook. 7. Communicating Watch carefully as you travel home from school or walk down your street. What examples of wave reflection and refraction do you notice? Describe each of these in your Science Journal and explain your reasons. For more help, refer to the Science Skill Handbook. Figure 17 Some airplane pilots use special ear protectors that interfere with engine noise but don’t block human voices. Content Have students draw dia- grams illustrating the refraction, reflection, diffraction, and inter- ference of waves. Use Perfor- mance Assessment in the Science Classroom, p. 127. Answers to Section Assessment 1. The rough surface scatters light in all directions. 2. Sound diffracts easily around objects such as buildings. 3. refraction 4. Diffraction is the bending of waves around a barrier. A wave is diffracted more when its wavelength is similar in size to the barrier or opening. 5. Waves of light travel in straight lines. The waves of light that come through the window travel in straight lines until they reach objects that absorb or reflect them. Also, the light waves have very small wave- lengths, so very little diffraction occurs as they move through a wide opening such as a window. 6. Because the light rays refract toward the normal, their speed must be lower in the glass than in water. 7. Answers might include reflection of light off a puddle or window or refraction of light through a prism. Others may mention the reflection of sirens, horns, or traffic noise. Recognize the Problem Purpose Students will model the behavior of seismic waves by creating transverse standing waves on a demonstration spring or coiled toy spring. Factors such as length, type of spring, and frequency will be varied and con- trolled to determine how the speed of a wave within a coil depends upon such factors. By comparing their results with those of others, students can make generalizations about waves within a spring, and by analogy, seismic waves within the earth. Process Skills observing, measuring, calculat- ing, separating and controlling variables, predicting Time Required 45 minute class Materials Demonstration springs sold by science educational supply com- panies create the best waves. Toy springs can also be used to create waves, and if springs are not available, a length of rope or hose will serve as a substitute wave maker. A metric tape mea- sure can replace a meterstick. Safety Precautions Caution students to not use or swing the spring anywhere but on the floor. Form a Hypothesis Possible Hypothesis The hypothesis of most students will reflect that the speed of a wave is determined by dividing the distance the wave travels by the time it takes for the wave to travel one wavelength. W hen an earthquake occurs, the waves of energy are recorded at points all over the world by instruments called seismographs. By comparing the data that they collected from their seismographs, scientists discovered that the interior of Earth must be made of layers of different materials. How did the seismographs tell them that Earth is not the same material all the way through? Recognize the Problem Can the speed of a wave be used to identify the medium through which it travels? Form a Hypothesis Think about what you know about the relationship between the frequency, wave- length, and speed of a wave in a medium. Make a hypothesis about how you can measure the speed of a wave within a medium, and use that information to identify an unknown medium. Materials coiled spring toy meterstick stopwatch tape *clock with a second hand *Alternate materials Safety Precautions Goals I Measure the speed of a wave within a coiled spring toy. I Predict whether the speed you measured will be different in other types of coiled spring toys. 26 N O CHAPTER 1 Waves Wave Speed 26 N O CHAPTER 1 Waves Internet Addresses Explore the Glencoe Science Web site at science.glencoe.com to find out more about topics in this activity. Chapter Resources Booklet Activity Worksheet, pp. 7–8 Lab Management and Safety, p. 65 Resource Manager Test Your Hypothesis Analyze Your Data Draw Conclusions Do 1. Make sure your teacher approves your plan before you start. 2. Carry out the experiment. 3. While you are doing the experiment, record your observations and mea- surements in your data table. Plan 1. Make a data table in your Science Journal like the one shown. 2. In your Science Journal, write a detailed description of the coiled spring toy you are going to use. Be sure to include its mass and diame- ter, the width of a coil, and what it is made of. 3. Decide as a group how you will measure the frequency and length of waves in the spring toy. What are your variables? Which variables must be controlled? What variable do you want to measure? 4. Repeat your experiment three times. 3. Average the wave speeds from your trials to determine the average speed of a wave in your coiled spring toy. wavelength ϫᎏ ϭᎏ 1. Calculate the frequency of the waves by dividing the number of vibrations you timed by the number of seconds you timed them. Record your results in your data table. 2. Use the following formula to calcu- late the speed of a wave in each trial. 1. How do the variables affect the wave speed in spring toys? Was your hypothesis supported? 2. Would it make a difference if an earthquake wave were transmitted through Earth’s solid mantle or the molten outer core? ACTIVITY O N 27 Trial 1 Trial 2 Trial 3 Length spring was stretched (m) 3.30 3.30 3.91 Number of crests 2 3 4 Wavelength (m) 3.30 2.20 1.96 # of vibrations timed 10 10 10 # of seconds vibrations were timed 5.49 3.60 6.01 Wave speed (m/s) 6.01 6.12 6.29 Wave Data wave wave frequency speed Post a description of your coiled spring toy and the results of your experiment on a bul- letin board in your classroom. Compare and contrast your results with other students in your class. Test Your Hypothesis Possible Procedures Help your student groups create standing waves. While a student holds one end of the coiled- spring toy stationary, have another student move the other end from side to side with a rhythm that produces a standing wave. Tie to Prior Knowledge Most students will have observed waves moving through a medium such as ocean waves or ripples on a pond. Expected Outcome Students will create standing transverse waves and measure their frequency, wavelengths, and speeds. From this data, they will predict the speed of waves in other types of coiled springs. Analyze Your Data 1. Based on the sample data in the table, frequencies were as follows:Trial 1, 1.82 Hz;Trial 2, 2.78 Hz;Trial 3, 1.66 Hz. 2. Based on the sample data in the table, speeds were as follows:Trial 1, 6.01 m/s; Trial 2, 6.12 m/s; Trial 3, 6.29 m/s. 3. Average wave speed is 6.14 m/s. Error Analysis Ask student groups to compare data with other groups and explain any significant discrep- ancies. Draw Conclusions 1. Answers will vary. 2. Yes, a transverse wave would not be transmitted through Earth’s molten core. ACTIVITY O N 27 Oral Ask students how they might determine the speed of water waves that are crashing ashore at a beach. Time the waves coming ashore to determine the frequency. Estimate the distance between wave crests to determine wavelength. The product of these two numbers is the speed of the wave. Use PASC, p. 89 Encourage students to record their data in electronically designed spreadsheets. Content Background Electromagnetic, ocean, and sound are different types of waves. Each of these waves propagate in a different manner. Electromagnetic waves do not require a media for travel and can carry energy through the vacuum of space. The following names of these waves are famil- iar to us: radio, microwave, infrared, visible light, ultraviolet, X rays, and gamma rays. Surface ocean waves are a mixture of longitudinal and transverse waves that carry energy through the water. Sound waves are lon- gitudinal waves that can carry energy through solids, liquids, and gases. The velocity of waves can be determined by the equa- tion velocity ϭ wavelength ϫ frequency. Discussion Waves are described by their frequency (pulses per second), wavelength (distance from two corresponding points on two successive waves), amplitude (distance from trough or crest to baseline), and speed. What do the numbers represent in each of the examples? 34 meters, amplitude; 966 km/h, speed; 800 pulses per second, frequency; 8 km/s and 4.8 km/s, speed Extension Have students research the speeds of light and sound. The speed of light is 3.00 ϫ 108 m/s. The speed of sound varies with the type of medium and other conditions such as density, temperature, and pressure. Waves, Waves, and More Waves Did you know... . . . You are constantly surrounded by a sea of waves even when you’re on dry land! Electromagnetic waves around us are used to cook our food and transmit signals to our radios and televisions. Light itself is an electromagnetic wave. . . . Waves let dolphins see with their ears! A dolphin sends out ultrasonic pulses, or clicks, at speeds of 800 pulses per second. These sound waves echo back to the dolphin after they hit another object. This process— echolocation—allows dolphins to recognize obstacles and meals. 28 N O CHAPTER 1 Waves . . . Tsunamis—huge ocean waves—travel at speeds near 966 km/h. . . . The highest recorded ocean wave was 34 meters high, which is comparable to the height of a ten-story building. This super wave was seen in the North Pacific Ocean and recorded by the crew of the naval ship USS Ramapo in 1933. 28 N O CHAPTER 1 Waves Internet Addresses Explore the Glencoe Science Web site at science.glencoe.com to find out more about topics in this feature. Do the Math Teaching Strategies Remind students that dis- tance ϭ velocity ϫ time, and that there are 3,600 seconds in an hour. Answers 1. 32 pulses 2. 4.7 h at 966 km/h 3. Students should make a bar graph with tsunamis traveling 966 km/h, P waves at 28,800 km/h, and S waves at 17,280 km/h. Go Further Have students find the fre- quency of radio waves. Are these waves low frequency or high frequency waves in the electromagnetic spec- trum? low SCIENCE STATS O N 29 . . . Earthquakes are caused by a variety of seismic waves— waves of energy that ripple through Earth after sub-surface rock breaks suddenly. The fastest are P and S waves. P waves are compressional waves that travel at about 8 km/s. S waves, which move like ocean waves, travel at about 4.8 km/s. . . . Radio waves from space were discovered in 1932 by Karl G. Jansky, an American engi- neer. His amazing discovery led to creation of radio astronomy, a field that explores parts of the universe that are hidden by interstellar dust or too distant for optical observation. W a v e l e n g t h s ( c m ) Radio waves Infrared waves Microwaves Visible waves Electromagnetic Wavelengths Type of wave 0.000 001 0.000 01 0.000 1 0.001 0.01 0.1 1.0 10.0 100.0 1,000.0 10,000.0 100,000.0 10 to 10,000 cm 1 cm 0.01 cm 0.0001 cm 1. A museum with a dolphin exhibit plays dolphin clicks for its visitors at a speed 250 times slower than the speed at which the dolphins emit them. How many clicks do the visitors hear in 10 s? 2. Tsunamis form in the ocean when an earthquake occurs on the ocean floor. How long will it take a tsunami to travel 4,500 km? 3. Make a bar graph to show the speeds of P waves, S waves and tsunamis. Use km/h as your unit of speed. Go Further Go to science.glencoe.com to learn about discoveries by radio astronomers. Graph the distances of these discoveries from Earth. Connecting To Math SCIENCE STATS O N 29 Electromagnetic Wavelengths How many times greater is the wavelength of infrared waves than that of visible waves? 100 times How many times greater is the wavelength for microwaves compared to infrared waves? 100 ti mes How many times greater is the wavelength for microwaves compared to visible waves? 10,000 times Preview Students can answer the ques- tions in their Science Journals. Discuss the answers as you go through the chapter. Linguistic Review Students can write their answers, then compare them with those of other students. Interpersonal Reteach Students can look at the illus- trations and describe details that support the main ideas of the chapter. Visual-Spatial Answers to Chapter Review SECTION 1 4. The boat moves perpendicular to the direction of motion of the waves. SECTION 2 4. amplitude SECTION 3 1. The surface is rough, so the light waves bounce off in many directions. LS LS LS After students have read the chapter and completed the Foldable described in Before You Read, have them do the activity on the student page. FOLDABLES Reading & Study Skills FOLDABLES Reading &Study Skills After You Read After You Read 30 N O CHAPTER STUDY GUIDE Chapter Study Guide 1 1 30 N O CHAPTER STUDY GUIDE 5. Waves travel through different materials at different speeds. Section 3 Wave Behavior 1. Reflection occurs when a wave strikes an object or surface and bounces off. Why doesn’t the foil show a clear image? 2. The bending of a wave as it moves from one medium into another is called refraction. A wave changes direction, or refracts, when the speed of the wave changes. 3. The bending of waves around a barrier is called diffraction. 4. Interference occurs when two or more waves combine and form a new wave when they overlap. Section 1 What are waves? 1. Waves are rhythmic disturbances that carry energy but not matter. 2. Mechanical waves can travel only through matter. Electromagnetic waves can travel through matter and space. 3. In a mechanical transverse wave, matter in the medium moves back and forth at right angles to the direction the wave travels. 4. In a compressional wave, matter in the medium moves forward and backward in the same direction as the wave. How does the boat in the picture move as the water wave goes by? Section 2 Wave Properties 1. The amplitude of a transverse wave is one half the distance between a crest and a trough. 2. The energy carried by a wave increases as the amplitude increases. 3. Wavelength is the distance between neigh- boring crests or neighboring troughs. 4. The frequency of a wave is the number of wavelengths that pass a given point in 1 s. What characteristic of a wave is indicated in the figure at the top of the next column? After You Read Use your Concept Map Study Fold to compare and contrast transverse and compressional mechanical waves. FOLDABLES Reading & Study Skills Study Guide Chapter 1 1 Using Vocabulary 1. Reflection 2. compressional wave 3. wavelength 4. amplitude 5. electromagnetic wave See student page. CHAPTER STUDY GUIDE O N 31 Chapter Study Guide 1 1 CHAPTER STUDY GUIDE O N 31 Vocabulary Words a. amplitude g. mechanical wave b. compressional wave h. reflection c. diffraction i. refraction d. electromagnetic wave j. transverse wave e. frequency k. wave f. interference l. wavelength Using Vocabulary Using the list, replace the underlined words with the correct vocabulary words. 1. Diffraction is the change in direction of a wave when it strikes a surface. 2. The type of wave that has rarefactions is a transverse wave. 3. The distance between two adjacent crests of a transverse wave is the frequency. 4. The more energy a wave carries, the greater its wavelength is. 5. A mechanical wave can travel through space without a medium. After you’ve read a chapter, go back to the beginning and speed-read through what you’ve just read. This will help your memory. Study Tip Complete the following spider map about waves. Reflection Refraction Diffraction Interference Move only through matter Transverse Compressional Sound waves Water waves M e c h a n i c a l w a v e s B e h a v i o r Wavelength Frequency Amplitude Speed Move through matter and space Radio waves Ultraviolet waves X rays Visible light Infrared waves Waves E l e c t r o m a g n e t i c w a v e s P r o p e r t i e s Study Guide Chapter 1 1 11. Compressional; each car is pushed into the next.The cars then rebound.This is like a compressional wave. 12. Yes; yes; electromagnetic waves can travel through space and matter. 13. The frequency decreases because fewer waves pass a given point in 1 s. 14. because the rough surface reflects the light rays in many different directions 15. Light travels much faster than sound, so the flash of the cannon will reach you before the sound will. 1. D 2. C 3. B 4. B 5. A 6. D 7. A 8. C 9. D 10. A 32 N O CHAPTER ASSESSMENT Portfolio Encourage students to place in their portfolios one or two items of what they con- sider to be their best work. Examples include: • Activity, p. 10 • Extension, p. 14 • Science Journal, p. 16 • Challenge, p. 25 Performance Additional performance assess- ments, Performance Task Assessment Lists, and rubrics for evaluating these activities can be found in Glencoe’s Performance Assessment in the Science Classroom. Chapter Planner Chapter Assessment 1 1 Choose the word or phrase that best answers the question. 1. What is the material through which mechanical waves travel? A) charged particles C) a vacuum B) space D) a medium 2. What is carried from particle to particle in a water wave? A) speed C) energy B) amplitude D) matter 3. What are the lowest points on a transverse wave called? A) crests C) compressions B) troughs D) rarefactions 4. What determines the pitch of a sound wave? A) amplitude C) speed B) frequency D) refraction 5. What is the distance between adjacent wave compressions? A) one wavelength C) 1 m/s B) 1 km D) 1 Hz 6. What occurs when a wave strikes an object or surface and bounces off? A) diffraction B) refraction C) a change in speed D) reflection 7. What is the name for a change in the direc- tion of a wave when it passes from one medium into another? A) refraction C) reflection B) interference D) diffraction 8. What type of wave is a sound wave? A) transverse C) compressional B) electromagnetic D) refracted 9. When two waves overlap and interfere destructively, what does the resulting wave have? A) a greater amplitude B) more energy C) a change in frequency D) a lower amplitude 10. What is the difference between blue light and green light? A) They have different wavelengths. B) One is a transverse wave and the other is not. C) They have different pitch. D) One is mechanical and the other is not. 11. Explain what kind of wave—transverse or compressional—is produced when an engine bumps into a string of coupled rail- road cars on a track. 12. Is it possible for an electromagnetic wave to travel through a vacuum? Through matter? Explain your answers. 13. Why does the frequency of a wave decrease as the wavelength increases? 14. Why don’t you see your reflected image when you look at a white, rough surface? 15. If a cannon fires at a great distance from you, why do you see the flash before you hear the sound? 16. Solving One-Step Equations A microwave travels at the speed of light and has a wave- length of 0.022 m. If the wave speed is equal to the wavelength times the frequency, what is the frequency of the microwave? 32 N O CHAPTER ASSESSMENT Assessment Chapter 1 1 20. Use Performance Assessment in the Science Classroom, p. 127. 16. about 13.6 billion Hz 17. Wave A is an electromagnetic wave and wave B is a mechanical wave. 18. The vibrating object moves back and forth, colliding with the mole- cules in the air around it. As the object moves forward, it pushes molecules together to form a com- pression. As the object moves back toward its original position and beyond, it creates a rarefaction— a region in which molecules are spread farther apart. 19. Because their longer wavelengths are closer to the size of buildings and mountains, AM radio waves dif- fract around them more than FM radio waves do. CHAPTER ASSESSMENT O N 33 Reproducible Masters Chapter Resources Booklet Chapter Review, pp. 35–36 Chapter Tests, pp. 37–40 Assessment Transparency Activity, p. 47 Glencoe Science Web site Interactive Tutor Chapter Quizzes Glencoe Technology Assessment Transparency Interactive CD-ROM Chapter Quizzes ExamView Pro Test Bank Vocabulary PuzzleMaker Software MindJogger Videoquiz DVD/VHS Resources Chapter Assessment 1 1 The Test-Taking Tip was written by The Princeton Review, the nation’s leader in test preparation. 1. A 2. J CHAPTER ASSESSMENT O N 33 17. Forming Hypotheses Form a hypothesis that can explain this observation. Waves A and B travel away from Earth through Earth’s atmosphere. Wave A continues on into space, but wave B does not. 18. Recognizing Cause and Effect Explain how the object shown below causes compres- sions and rarefactions as it vibrates in air. 19. Comparing and Contrasting AM radio waves have wavelengths between about 200 m and 600 m, while FM radio waves have wavelengths of about 3 m. Why can AM radio signals often be heard behind buildings and mountains but FM radio signals cannot? 20. Making Flashcards Work with a partner to make flashcards for the bold-faced terms in the chapter. Illustrate each term on the front of the cards. Write the term and its defini- tion on the back of the card. Use the cards to review the terms with another team. Kamisha’s science teacher told her that her remote control sent signals to the TV and VCR by using infrared waves. She decided to do some research about waves. The information she gathered is shown in the diagram below. 1. According to the diagram, which type of wave has a wavelength greater than 1 m? A) radio B) infrared C) ultraviolet D) X ray 2. According to the diagram, which type of wave has the HIGHEST frequency? F) radio G) ultraviolet H) X ray J) gamma ray 1 2 3 4 10 2 10 -2 10 -4 10 -6 10 -8 10 -10 10 -12 10 -14 10 6 10 8 10 10 10 12 10 16 10 18 10 20 10 22 Frequency (Hz) Wavelength (m) Radio TV/FM Radar Infrared Visible light Ultraviolet X ray Gamma ray 1 m Go to the Glencoe Science Web site at science.glencoe.comor use the Glencoe Science CD-ROMfor additional chapter assessment. TECHNOLOGY Assessment Chapter 1 1 Test Practice