11. The melting point of a substance is the same as its. 12. As the temperature of an object increases, the amount of heat in the object.

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1 11. The melting point of a substance is the same as its A boiling point C both A and B B freezing point D none of the above 12. As the temperature of an object increases, the amount of heat in the object. A increases C stays the same B decreases D makes the mass increase 13. A material that keeps heat out of a house in summer and cold out in winter. A is a good conductor C has a low freezing point B is a good insulator D has a high boiling point Critical Thinking Write the answer to each of these questions on your paper. 14. Why does ice cream melt faster in a dish that is room temperature than in a dish that has been in the freezer? 15. The objects shown below have the same temperature. Do they give off the same amount of heat? Explain your answer. Studying together in small groups and asking questions of one another is one way to review material for tests. Heat Chapter 6 157

2 Chapter Sound and Light Almost everyone enjoys watching a fireworks display. Fireworks help us celebrate special holidays and events. What happens when you view fireworks? First, you see an explosion of bright, colorful light. Then, you hear the explosion's crashing boom or sharp whistle. In Chapter 7, you will learn how sound is produced and how light travels. You also will discover how sound and light are alike and how they are different. Organize Your Thoughts Vibrating matter Photons Reflected Reflected II Refracted Goals for Learning To explain how sound is produced To tell how sound travels To describe the nature of light To explain reflection of light To explain refraction of light 158

3 What Is Sound? Objectives After reading this lesson, you should be able to + explain what sound is. + explain how sound is produced. + explain how sound energy moves in waves. Vibrate To move rapidly back and forth You hear many kinds of sounds every minute of every day. Rut do you know what sound is? Sound is a form of energy. Scientists who study sound also study human hearing and the effect of sound on different objects. How Sound Is Produced All the sounds you hear are made when matter vibrates. To vibrate means to move quickly back and forth. Look at the figure of the bells. When the clapper hits the bell, energy from the clapper causes the bell to vibrate. When the bell vibrates, it moves back and forth. The bell pushes the air around it. You can see in the figure that as the bell vibrates to the right, it pushes together the air particles to the right of the bell. When it vibrates back to the left, the air particles to the right of the bell move apart. Those particles to the left of the bell are squeezed together. As the bell continues to vibrate, the air particles on each side are squeezed together and spread apart many times. Air particles are pushed together Air particles move apart Air particles are pushed together Air particles move apart Sound and Light Chapter 7 159

4 Sound wave A wave produced by vibrations The strength of a sound is known as its intensity. Scientists measure the intensity of sounds in units called decibels. The sound of rustling leaves would be measured at about 20 decibels. The roar of a jet engine would be approximately 1 35 decibels. How Sound Travels The movement of the air molecules around a vibrating object is a sound wave. You cannot see a sound wave. Sound waves move out from the vibrating object in all directions. As the sound waves travel farther from the object, they become weaker. The figures of the wire spring show how sound energy travels in waves. In Figure A, the wire is pinched together at one end. In Figure B, the "wave" moves across the spring. Figure A Figure B Some things make sounds even though you cannot see them vibrate. For example, if you strike a tuning fork, you will not see it vibrate. But you will hear the sound it makes. You can see evidence of sound waves by placing the end of a tuning fork that has been struck into a small container filled with water. You will notice water splashing out of the container. The vibrations of the tuning fork cause the water to move about. When a tuning fork vibrates, it produces sound waves. 160 Unit 1 Physical Science

5 Lesson 1 Write your answers to these questions in complete sentences on a sheet of paper. 1. How is sound produced? 2. How does sound travel? 3. What is a sound wave? 4. What word means "to move quickly back and forth"? 5. What happens to the strength of sound waves as they travel farther from the vibrating object? The Doppler Effect The Doppler effect, described by Christian Doppler in 1842, is an apparent change in wave frequency. The Doppler effect occurs with all types of waves: sound, light, or radio waves. This effect happens when the sound source is moving or when the observer is moving. The relative motion of the waves' source and the observer causes the frequency change. As the wave source moves forward, the waves in the front of it get crowded. When the waves move closer together, the frequency of the waves increases. As the source of the waves moves away, the waves spread apart. These waves have a lower frequency. Scientists use the Doppler effect in many ways. They use it to study the speed and direction of a star. They measure the change that motion causes to the frequency of the star's light. Meteorologists use Doppler radar to track storms by finding changes in wind speed or direction. Police use Doppler radar to measure a car's speed. Edwin Hubble used the Doppler effect to show that the universe is expanding. Sound and Light Chapter 7 161

6 INVESTIGATION Inferring How Sound Waves Travel safety glasses pencil with sharpened point large plastic-foam cup 2 rubber bands (one cut) plastic food wrap salt plastic beaker water tuning fork Purpose Can sound waves travel through matter? This investigation will demonstrate that sound waves are vibrations that travel through matter. Procedure 1. Copy the data table on a sheet of paper. How the Rubber Band Was Plucked 2. Put on your safety glasses. Observations 3. Use the point of the pencil to punch a small hole in the bottom of the cup. 4. Push one end of the cut rubber band through the hole in the cup. Tie a knot in the end of the rubber band so that it cannot be pulled through the hole. The knot should be inside the cup. 5. Stretch a piece of plastic wrap tightly over the top of the cup. Use the other rubber band to hold the plastic wrap in place, as shown in the figure on the next page. 6. Hold the cup with the plastic wrap facing up. Sprinkle a few grains of salt on the plastic wrap. 162 Unit 1 Physical Science

7 7. Hold the cup while your partner slowly stretches the rubber band. Gently pluck the stretched rubber band and observe what happens to the salt. Record your observations in the data table. 8. Vary the force used to pluck the rubber band. Notice the difference in sound the rubber band makes as you vary the force. Questions and Conclusions 1. In Step 7, what happened to the salt when you plucked the rubber band? 2. What do you think caused the salt to move? Explain your answer. 3. In Step 8, how did the force you used to pluck the rubber band affect the sound it made? 4. In Step 8, how did the force you used to pluck the rubber band affect the salt on the plastic wrap? Explore Further 1. Use a tuning fork and a plastic beaker half-filled with water. Gently tap the tuning fork against the heel of your hand and place the tips of the fork into the beaker of water. What happens to the water? 2. Vary the force used to tap the tuning fork. Notice what happens to the water as you vary the force. Sound and Light Chapter 7 163

8 Lesson Light Objectives After reading this lesson, you should be able to + define light and explain how visible light is produced. + describe the nature of light. ^ explain how light waves travel. + describe the visible spectrum. Light A form of energy that can be seen Reflect To bounce back Photons Small bundles of energy that make up light You see light everywhere. You see objects because light is reflected, or bounced back, from them. But what is light? Light is a form of energy that you can sometimes see. Most visible light is produced by objects that are at high temperatures. The sun is the major source of light on Earth. The sun loses energy by emitting light. The sun's energy arrives as light with a range of wavelengths, consisting of visible light, infrared, and ultraviolet radiation. Light as a Particle Scientists have done experiments to gather information about light. Some scientific experiments suggest that light acts like a particle. Evidence tells scientists that light is made up of bundles of energy called photons. Photons are like small particles. A single photon is too small to be seen. Look at the light coming from the flashlight. Streams of photons make up each beam of light. Each photon carries a certain amount of energy. 164 Unit 1 Physical Science

9 Light takes less than two seconds to reach the earth from the moon. Light takes about eight minutes to travel from the sun to the earth. Light from the nearest star takes more than four years to reach the earth. Light as a Wave Other scientific evidence suggests that, like sound, light travels in waves. As a result of their findings, most scientists agree that light seems to have properties of both particles and waves. Scientists agree that light travels as waves in a straight line. Most properties of light can be explained in terms of its wave nature. Waves including waves in water, earthquake waves, sound waves, and light waves transfer energy when they interact with matter. Light waves move like water waves. Light waves move like waves in water. However, light waves travel fastest through empty space. Light waves move more slowly as they pass through matter. In fact, light waves cannot pass through some matter at all. Light waves travel more quickly than sound waves. Light waves travel about 300,000 kilometers per second. This is the fastest possible speed anything can travel. Sound and Light Chapter 7 165

10 Visible spectrum The band of colors that make up white light; the colors in a rainbow Prism A dear piece of glass or plastic thai can be used to separate white light Colors in White Light The light you see from the sun is white light. Did you know that white light is actually made up of many colors of light? If you have ever seen a rainbow, you have actually seen the colors that make up white light. How is color determined? Usually it is determined by which colors of light an object absorbs or reflects. A red ball is red because it absorbs all colors of the visible spectrum but red. A rainbow contains all the colors of the visible spectrum. The band of colors you see in a rainbow is known as the visible spectrum. The colors of the visible spectrum always appear in the following order: red, orange, yellow, green, blue, indigo, and violet. You can use a prism like the one in the photo to see the colors in white light. A prism is a piece of glass or plastic that can separate white light into the colors of the visible spectrum. A prism shows the colors in white light. 166 Unit I Physical Science

11 Science in Your Life What are lasers and how do we use them? A laser is a device that produces a powerful beam of light. Laser light is unique. Wavelengths in ordinary white light differ from one another. They also overlap each other. Wavelengths in laser light are all the same and are in step. The crests, or tops, and the troughs, or bottoms, of the waves are lined up exactly. Lasers have many uses. We can use lasers to find gas leaks and detect pollutants in the air. Lasers can monitor and identify air pollutants around landfills, factories, and highways. Unlike a flashlight, the concentrated light of a laser can travel miles and miles. So lasers that monitor air pollution do not have to be near the pollution's source. The table shows some other uses for lasers. Communication and entertainment Business Medicine Scientific research Some Other Uses for Lasers transmitting telephone and TV signals producing and reading compact discs identifying bar codes on products doing sales transactions making maps surveying land printing and scanning detecting medical problems, diseases, and disorders doing surgery, such as removing cataracts from eyes, removing cancerous cells, clearing blocked arteries, removing tonsils treating skin conditions including removal of birthmarks collecting data from the moon studying the atom studying chemical reactions Sound and Light Chapter 7 167

12 Lesson 2 R E V I E W Write your answers to these questions in complete sentences on a sheet of paper. 1. What makes up a beam of light? 2. How does light travel? 3. Would light travel faster through space or through a window? Explain your answer. 4. What colors make up white light? 5. Explain what a prism does. 168 Unit 1 Physical Science

13 Lesson How Light Is Reflected Objectives After reading this lesson, you should be able to + describe how plane mirrors reflect light. ^ describe how concave and convex mirrors reflect light. + explain how light is refracted, + describe how concave and convex lenses refract light. What happens when you look into a mirror? Why can you see yourself? The answers to these questions have to do with the way light waves act. Light Bounces When you throw a ball to the floor, it bounces back. Light also bounces back when it hits an object. When light bounces off a surface, we say that the light is reflected. Reflection is the bouncing back of a light wave. Few objects give off their own light. We see most objects only because of the light they reflect. The figure below illustrates how light is reflected. Like a tennis ball, light waves bounce off a surface at the same angle that they hit the surface. Sound and Light Chapter 7 169

14 Image A copy or likeness Plane mirror Aflat, smooth mirror Concave mirror A mirror that curves in at the middle Convex mirror A mirror that curves outward at the middle Refraction The bending of a light wave as it moves from one material to another Eye of observer You can see an image, a copy or likeness, in a mirror because light waves are reflected. Study the figure below. Notice how light from the cup hits the mirror and is reflected toward the observer's eye. Then the eye forms an image. The cup looks as if it is behind the mirror. The image is the same size as the original cup, but it is reversed. The handle of the cup appears on the opposite side when it is seen in the mirror. The angle at which the light reflects back causes this reversal. Follow the lines of light in the figure to see how this happens. Types of Mirrors A mirror with a flat, smooth surface is called a plane mirror. The flatter the surface of the mirror, the clearer the image. Many mirrors have curved surfaces rather than flat surfaces. One kind of curved mirror is called a concave mirror. A concave mirror has a reflecting surface that curves inward, like the inside of a spoon. A concave mirror creates an image that looks larger than the real object. Mirror Image appears to be behind the mirror The reflecting surface of some mirrors curves outward like the outside of a spoon. These kinds of mirrors are called convex mirrors. A convex mirror creates an image that looks smaller than the real object. However, you can see much more area in a convex mirror. For this reason, rearviewand side-view mirrors on vehicles are often convex mirrors. Bending Light When light moves from one kind of matter to another, the light waves change speed. As a result, the direction of the light changes. The bending of a light wave as it moves from one material to another is called refraction. 170 Unit I Physical Science

15 Lens A curved piece of clear material that refracts light waves Concave lens A lens that is thin in the middle and thick at the edges Convex lens A lens that is thick in the middle and thin at the edges Concave lens Figure A Convex lens Notice that the pencil in the photo appears to be bent. Light travels more slowly in water than it does in air. When light passes from the water to the air, the light waves change speed and change direction. As a result, the pencil seems to bend. Lenses A lens bends light by acting like the water in the container. A lens is a curved piece of glass or other clear material that refracts light waves that pass through it. Refraction causes the pencil to look like it is bent. A concave lens curves inward. Look at Figure A. The lens is thin in the middle and thick at the edges. Light rays that pass through a concave lens are spread apart. When you look through a concave lens, objects appear to be smaller than they really are. Some people say the objects look "sharper." You can see this effect by looking through the glasses of someone who is nearsighted. A convex lens curves outward. Look at Figure B. The lens is thick in the middle and thin at the edges. Light rays that pass through a convex lens are refracted inward. A convex lens focuses light. If you hold a convex lens close to your eye, the lens will magnify an image. If you hold it far from your eye and observe an object at a distance, the image appears upside down. Convex lenses are used in eyeglasses for people who are tarsighted. Figure B Sound and Light Chapter 7 171

16 Lesson 3 REVIEW Write your answers to these questions in complete sentences on a sheet of paper. 1. How does a concave mirror differ from a convex mirror? 2. Why are side-view and rearview mirrors on vehicles often convex? 3. What is refraction? 4. How does a concave lens refract light? 5. How does a convex lens refract light? V -4 A A Y «A Y «A Y «A A Y Optician Opticians fit eyeglasses by following prescriptions written by ophthalmologists or optometrists. They also measure customers' eyes and recommend frames. Opticians write orders to laboratories for grinding and inserting lenses into frames. Some opticians grind and insert lenses themselves. Opticians make sure lenses are correctly ground and frames fit properly. Some opticians specialize in fitting contact lenses. Science at Work Most opticians complete an apprenticeship or receive on-the-job training. In some states, opticians must be licensed. Opticians must be courteous, patient, and have good communication skills. They need to work well with their hands and be very detailed. Opticians also must take measurements accurately and have a good understanding of physics. 172 Unit! Physical Science

17 Chapter 7 SUMMARY Sound is caused by vibrations. Sound travels in waves. People see objects because light is reflected from them. Light is made up of bundles of energy called photons. Light has properties of both particles and waves. Light waves travel fastest through empty space. The visible spectrum makes up white light. Reflection is the bouncing back of a light wave. Refraction is the bending of a light wave. A mirror is an object that reflects light. Three types of mirrors are plane, concave, and convex. Concave and convex lenses refract light and can correct vision. Science Words concave lens, 171 image, 170 concave mirror, 170 lens, 1 71 convex lens, 171 light, 164 convex mirror, 170 photons, 164 plane mirror, 1 70 prism, 166 reflect, 164 refraction, 1 70 sound wave, 160 vibrate, 159 visible spectrum, 166 Sound and Light Chapter 7 173

18 Chapter 7 REVIEW Word Bank concave lens concave mirror convex lens convex mirror light prism reflection refraction sound wave vibrates Vocabulary Review Choose a word or words from the Word Bank that best complete each sentence. Write the answer on a sheet of paper. 1. A separates white light into bands of colors. 2. A is thick in the middle and thin at the edges. 3. Sound is produced when matter. 4. The bouncing back of a light wave is called. 5. The reflecting surface of a curves inward. 6. A reflects light rays so objects appear smaller than they are. 7. The bending of a light wave is called. 8. Light rays that pass through a. are spread apart. 9. The movement of air particles around a vibrating object is a 10. is a form of energy that can be seen. 174 Unit I Physical Science Concept Review Choose the answer that best completes each sentence. Write the letter of the answer on your paper. 11. As sound travels farther away from its source, it. A loses strength C bends B gains strength D does not change 12. Sounds are made when matter _. A rotates B moves quickly back and forth C vibrates D both B and C 13. Light is made of tiny bundles of energy called _. A photographs C neurons B photons D none of the above

19 14. A straw sticking out of a glass of lemonade looks bent due to. A light traveling more slowly in water than in air B refraction C light waves changing speed and direction D all of the above 15. A vibrating object pushes against the around it. A sound waves C visible spectrum B lightwaves D air molecules 16. The bands of colors in a rainbow are known as _. A photons C the visible spectrum B prisms D waves 17. A lens lightwaves. A reflects B reverses 18. Sound travels in. A waves B particles Critical Thinking C absorbs D refracts C images D photons Write the answer to each of these questions on your paper. 19. Copy the drawing of each of these lenses. Draw lines to show how the light waves are refracted as they pass through each lens. Explain what you drew for each lens. What type of vision can each of the lenses help improve, and why? 20. Explain what is meant when something is called the mirror image of an object. When studying for a test, learn the most important points. Practice writing this material or explaining it to someone. Sound tun! Light Chapter 7 175

20 Chapter Electricity and Magnetism Lightning is an example of electricity static electricity. Electricity is all around us. Every day we use electricity. It lights homes and runs appliances. It starts cars and operates traffic signals. There are even electrical signals in our bodies that make our organs work. Do you know how electricity works and where it comes from? In Chapter 8, you will learn what electricity is, how it works, and how it travels. You will also learn about magnets and how they work. Organize Your Thoughts Electricity Magnetism Static electricity Electric current Magnetic poles Magnetic fields Series circuit Parallel circuit Goals for Learning To explain how electric current flows through a circuit To describe series circuits To describe parallel circuits To describe various kinds of magnets To explain what a magnetic field is To explain electromagnetism 176