Sound And Light.pdf

Sound and Light

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Sound and Light

Lesson 1 What Is Sound?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Lesson 2 What Is Light? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

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VOCABULARY VOCABULARY vibration volume pitch frequency

What Is Sound?

A vibration is a back-andforth movement of matter. A drum’s thin covering vibrates when someone hits it.

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The loudness of a sound is called volume. The jackhammer makes a sound loud enough to hurt your ears.

The pitch of a sound is how high or low it is.

The number of vibrations in a second is the frequency of a sound.

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READING FOCUS SKILL

MAIN IDEA AND DETAILS The main idea is what the text is mostly about. Details are pieces of information about the main idea. Look for information about what sound is and details

about the ways sound travels.

Sound Energy Sound is energy that travels through air. A sound is made when something vibrates. A vibration is a back-and-forth movement of matter. When a drummer hits the top of a drum, it causes the covering to vibrate. The vibrations make the air vibrate. This vibration is what makes the sound you hear.

The head of a C drum—a thin C covering—is C flexible and tight, C so it vibrates. C

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Instruments make sounds in different ways. A drum makes sound when you hit it. A guitar makes sound when you pluck the strings. A clarinet makes sound when you blow into it and a wood reed vibrates. The loudness of a sound is called volume. The volume of a sound is measured in decibels (dB). A high-decibal sound is loud and has a lot of energy.

What are three ways you can make sounds with a musical instrument?

How Loud Are Some Sounds? Sound

Decibel Level

Whisper

20 dB

Quiet radio

40 dB

Conversation

60 dB

Dishwasher

80 dB

Jackhammer

100 dB

Thunderclap

120 dB

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Sound Waves Sound moves through the air as waves. When you hit a drum, the covering vibrates and pushes the air above it. This squeezes molecules of air together. The squeezed air pushes the air next to it. In this way, the energy moves through the air. Have you ever noticed that some sounds are higher than others? For example, a trumpet makes a sound higher than a tuba does. A sound’s pitch is how high or how low it is. The number of vibrations in a second is the frequency of a sound. If you pluck a long string and a short string, the short string will vibrate faster. This means the short string has a higher frequency than the long string.

B The springs model how sound travels in compression waves.

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Frequency and pitch are related. A sound with a high frequency has a high pitch. A sound with a low frequency has a low pitch. Sound waves move out in all directions from an object. A sound that hits a hard surface bounces back. A sound that bounces off a surface is called an echo. You can often hear echoes in caves and canyons. What does an echo sound like compared with the original sound?

How is pitch related to frequency?

B Sound bounces off the hard cliff and produces an echo. The echo

is not as loud as the original sound.

) ) )

H

O o L l l L e E (h ((

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Sound Transmission Think about playing with a line of dominoes. When you push the first one, the next one falls down. Sound waves move like that. They travel through the air because particles in the air give energy to ones nearby. Sound energy can travel a long distance. But the particles stay in one place.

The sound moves through the air as compression waves. When the performer sings, she produces vibrations that compress the air.

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Any kind of matter can vibrate and carry sound. Matter that carries sound is called a medium. Sound waves need a medium to travel. The speed of sound depends on the medium. Sound travels fastest in solids and slowest in gases. Sound also moves faster when it’s warm than when it’s cold.

In what kind of medium, and at what kind of temperature, will sound travel the fastest?

The sound waves reach the people in the audience, and they hear the singer’s performance.

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Animals and Sound Many animals can hear sounds that humans cannot hear. Elephants can hear sounds with very low frequencies. Dogs can hear high-pitched sounds.

A grasshopper picks up vibrations through legs.

A snake uses its jaw to sense vibrations from the ground.

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Bats have excellent hearing. When a bat flies, it produces many sounds. These sounds bounce off objects, and the bat hears the echoes. This allows the bat to fly when it is dark.

The bat uses echoes to find prey.

Review Complete this main idea statement. 1.

travels through matter as a compression wave.

Complete these detail statements. 2. A sound with a

pitch has a high frequency.

3. When sound waves strike a soft surface, like a carpet, most of the sound energy is . 4. Sound needs matter, called a sound waves.

, to carry the

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2 VOCABULARY reflection opaque translucent transparent refraction convex lens concave lens

What Is Light?

Light bouncing off a surface is reflection.

When light moves into a different material, it bends. This bending of light is called refraction.

Materials that do not allow light to pass through are opaque. 12

Materials that allow only some light to pass through are translucent.

Materials that allow light to pass through are transparent.

A concave lens is thicker at the edges than at the center. It spreads light waves apart.

A convex lens is thicker at the center than it is at the edges. It bends light waves together. 13

READING FOCUS SKILL

MAIN IDEA AND DETAILS The main idea is what the text is mostly about. Details are pieces of information about the main idea. Look for information about light energy and details

about kinds of light waves and how matter affects light.

Light Energy Light is a form of energy that travels in waves. Unlike sound, light does not need a medium to travel. Light is part of the electromagnetic spectrum. The part of the spectrum we can see is called visible light. The waves that make up the spectrum have different frequencies. Radio waves have a lower frequency than visible light waves. Ultraviolet waves have a higher frequency than visible light waves. Waves with high frequencies carry more energy than waves with low frequencies.

What is another name for light we can see?

The part of the spectrum we see is called visible light. The rainbow shows the colors of visible light. B

Art: p/u diagram of rainbow from G5 SE p. 556 (227P). 14

A Transverse waves

Light Waves Light waves are different from sound waves. Light waves move like ocean waves. They move up and down. Light waves can travel through matter, like sound, or through empty space. The light from the sun travels through space. Light moves much faster than sound. Light waves move thousands of times faster than sound waves. It takes only about 8 minutes for light to travel from the sun to Earth. You can feel the energy in sunlight as heat. You can also feel the heat from a light bulb. The sun and the light bulb both send out light in all directions. But a laser gives off light in a narrow beam. This light is very powerful because its waves are so close together.

What are three ways that light is different from sound?

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Absorption, Reflection, and Refraction When light hits an object, the object affects the path of the light. The object can absorb the light, make it bounce back, or let it pass through. When light passes through an object, some of the light is absorbed. Darkcolored objects absorb the most light. So it is better to wear a light-colored shirt on a hot day. Reflection occurs when light bounces off a surface. In most cases, light spreads out when it is reflected. But a smooth surface does not spread light out. This is why you can see yourself in a mirror. Most objects absorb some light and reflect the rest. Opaque materials do not let any light pass through them. You cannot see through opaque objects. Most objects around you are opaque, such as your sneakers, your desk, and this book.

The glass in the C building causes C light to reflect C off its surface. C 16

Transparent materials let light pass through. Most kinds of glass are transparent. Translucent materials let only some light pass through. Stained glass windows and waxed paper are translucent. The difference between transparent and translucent materials is how they spread out light. Translucent materials spread light more. When light moves from one material to another, it bends. This bending is called refraction. Refraction changes the angle at which you see things. When you look at an object through two different materials, a straight object can seem bent. Have you ever looked at a straw in a glass of water? It seems to bend where the straw enters the water. This is refraction.

What are the three ways light reacts when it hits an object? The pelican’s body looks separated because of refraction. B

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Lenses Have you ever used a hand lens to see something small? The hand lens makes objects look larger. Hand lenses have a plastic or glass lens in them. The lens is transparent and curved. The curve allows the lens to bend light. The shape of the curve determines how light will bend. There are two basic types of lenses. A convex lens is thicker at the center than it is at the edges. It bends light waves to bring them together. A hand lens uses a convex lens. Convex lenses are also used to make an image on a screen, like at the movies. In a camera, convex lenses bring light together onto film to produce a photo.

A convex lens brings light waves together. B

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A concave lens is thicker at the edges than it is at the center. It spreads light waves apart. In a camera, the viewfinder uses a concave lens. This lens makes objects look smaller so you can see what the whole picture will look like.

What type of lens is used in a hand lens?

D A concave

lens spreads light waves apart.

Review Complete this main idea statement. 1. ______ travels through matter or empty space as a transverse wave.

Complete these detail statements. 2. ______ waves move thousands of times faster than ______ waves. 3. A magnifer uses a ______ lens to make objects appear larger. 4. An object that does not allow any light to pass through it is ______. 19

GLOSSARY concave lens (kahn•KAYV LENZ) a lens that is thicker at the edges than it is at the center. convex lens (kahn•VEKS LENZ) a lens that is thicker at the center than it is at the edges. frequency (FREE•kwuhn•see) the number of vibrations in a second. opaque (oh•PAYK) not allowing light to pass through. pitch (PICH) how high or low a sound is. reflection (rih•FLEK•shuhn) the bouncing of heat or light off an object. refraction (rih•FRAK•shuhn) the bending of light as it moves from one material to another. translucent (tranz•LOO•suhnt) allowing only some light to pass through. transparent (tranz•PAR•uhnt) allowing light to pass through. vibration (vy•BRAY•shuhn) a back-and-forth movement of matter. volume (VAHL•yoom) the loudness of a sound.

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Think About the Reading 1. What can you do to help you remember what you have learned in this chapter? 2. What questions do you have after reading this book? How can you find the answers to your questions?

Hands-On Activity Fill one glass half full with water and fill a second glass threequarters full with water. 1. Gently tap on the sides of the glasses with a spoon. Which glass has a higher pitch? Why? 2. Place the spoon into one of the glasses. Bend down and look at the glass straight on. What does the spoon look like? Why?

School-Home Connection Explain to an older family member what you have learned about sound and light. Walk through your house with the family member. Take turns identifying materials in your house that are transparent, translucent, and opaque.