Physical Science by Timothy Sandow Genre Comprehension Skill Text Features Science Content Nonfiction Compare and Contrast Captions Labels Sound Diagram Glossary Scott Foresman Science 3.14 ì<(sk$m)=bdieha< +^-Ä-U-Ä-U ISBN 0-328-13847-9
Vocabulary compression wave pitch Sound by Timothy Sandow vibration Illustrations: 7, 14 Jeff Mangiat Photographs: Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Unless otherwise acknowledged, all photographs are the property of Scott Foresman, a division of Pearson Education. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R) Background (Bkgd) Opener: Jake Rajs/Getty Images; Title Page: DK Images; Lynn Stone/Index Stock Imagery; 2 Joseph Sohm/ChromoSohm Inc./Corbis; 4 (CL, BR) DK Images; 5 Getty Images; 6 Getty Images, 8 Getty Images; 9 (CL, CC, BL) Getty Images; 11 Robert Brenner/PhotoEdit; 12 P. Freytag/Zefa/ Masterfile Corporation; 13 Scott Tysick/Masterfile Corporation; 15 (CL) Mark Tomalty/Masterfile Corporation, (CC) Christiana Carvalho-Frank Lane Picture Agency/Corbis, (BR) DK Images, (BL) Stone/Getty Images ISBN: 0-328-13847-9 Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, write to: Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025. 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
What causes sounds? Take a walk in the city. Cities are noisy. Car horns honk. Buses and garbage trucks roar by. People talk on the street. It is much quieter in the country. Birds chirp. Cows moo. Water trickles in a creek. Sounds are everywhere. Some sounds you hear may hurt your ears. You may like other sounds. Each sound you hear is different. Sounds are also alike in some ways. Noisemakers are sometimes used on New Year s Eve. Do you like the sounds they make? 2 3
The Causes of Sound Sound happens when matter moves back and forth very quickly. This movement is called a vibration. There must be movement to make sound. The instruments pictured make sounds. They can make high sounds. They can make low sounds. Pitch is how high or low a sound is. Objects that vibrate slowly make a low-pitched sound. Objects that vibrate quickly make sounds that have a higher pitch. Hitting or Plucking to Make Sound Some instruments make sounds when you hit them. They are called percussion instruments. Drums are percussion instruments. Drums are played with rubber hammers, wooden sticks, brushes, or your hands. If you tap a drum lightly, you hear a soft sound. Hitting the drum harder makes a stronger vibration. This makes a louder sound. You must hit or shake a tambourine to make a sound. The blocks on this instrument vibrate when they are hit with a rubber hammer. These drums are different shapes and sizes. Each one makes a sound with a different pitch when struck. 4 5
Stringed instruments are played in two ways. You can pluck the strings. Or you can rub a bow across them. Both ways make sounds. The strings are different sizes. They can be long or short and thick or thin. Some are stretched tighter than others. Long, thick strings make a lower-pitched sound. Short, thin, tight strings make faster vibrations. They make higher-pitched sounds. Using Air to Make Sound The sound of your voice is made by vibrations in your windpipes. When air from your lungs passes between your vocal cords, they vibrate. You can speak and sing because your vocal cords vibrate. When you speak, your cords tighten. The tighter they get, the higher the pitch of your voice. Your vocal cords are two pairs of thin tissue in your windpipe. Have you ever heard a harp before? The strings of this harp must be plucked to vibrate. 6 7
A wind instrument s sound comes from vibrating air inside it. Blow into a trumpet. Your lips vibrate against the mouthpiece as you blow. This makes the air inside the trumpet vibrate. It also makes sound. You can change the pitch of the trumpet s sound in two ways. Change how your lips vibrate. Or press on the valves of the trumpet. Pressing on the valves changes how long the air column is inside the trumpet. Some wind instruments use reeds. A reed is a thin piece of wood. It is attached to the mouthpiece. When a person blows on a reed, it vibrates. The vibration makes the air inside the wind instrument vibrate. The vibrating air makes a sound. If you press the keys of the wind instrument, you can change the pitch of the sound. All three of these wind instruments use reeds. Clarinet Do you know how to play a trumpet? Saxophone Harmonica 8 9
How does sound travel? What are sound waves? A bell rings. Its vibrations move in the air. Some air particles are spread out. Others are squeezed together. The particles take turns doing this. This allows the bell s vibrations to move between these particles. This movement makes a wave called a compression wave. Sound waves are compression waves. Sound waves travel through matter. Some of the particles that make up matter get squeezed. Other particles are spread apart. The particles of matter take turns being squeezed and spread out. The length of a sound wave can be measured. We measure from the center of one squeezed area to the center of the next. Sound travels as waves in the air. Wavelength Sound waves from a jackhammer have lots of energy. If you were standing nearby, you would hear a very loud sound. Sound waves lose energy as they move away. Farther away, the sound would not be as loud. 10 11
Sound and Matter You hear sound only when it travels through matter. Sound can travel through solids, liquids, and gases. The speed of a sound wave is different in each kind of matter. The gases of air have particles that are far apart. Sound travels slowly through gases. Liquid particles are closer together. Sound travels more quickly through a liquid than a gas. Solid particles are closer together than gases or liquids. Sound travels fastest through solids. Echoes are sound waves that hit something and bounce back. Scientists use sound waves and echoes to study the ocean. A ship sends out a sound wave. When the sound wave hits the bottom of the ocean, it bounces back. Scientists measure how long the sound wave takes to bounce back. Then they can figure out how deep the ocean is at that spot. Sound travels at about 1,530 meters per second in water. Some whales can make sounds that can be heard up to 160 kilometers away. Speed of Sound Material Solid Steel Liquid Seawater Gas Air Speed (meters per second) 5,200 1,530 340 Light travels faster than sound. That is why you may see fireworks before you hear them. 12 13
The Ear We hear sounds with our ears. The outer ear catches sound waves. The waves travel inside the ear to the eardrum. When the sound waves hit the eardrum, they make it vibrate. The vibrating eardrum makes little bones vibrate. The little bones touch the shell-like inner ear. It is filled with liquid and tiny hairs. The vibrating little bones make the tiny hairs move. The hairs are connected to nerves. The nerves carry signals to the brain. The brain recognizes the signals. Then we know what we are hearing. Many animals have vocal cords like people do. They make sounds when their vocal cords vibrate. Dogs bark. Cows moo. Some animals make sounds that do not use vocal cords. Bees and mosquitoes make buzzing sounds when their wings vibrate. Bats send out sounds people cannot hear. The sounds are high-pitched and bounce off insects. The sounds return to the bats ears. This helps the bats find their food. Many insects make sounds by rubbing body parts together. Eardrum Little bones Outer ear Chimpanzees grunt, bark, squeak, scream, and even laugh. Inner ear Zebras make sounds by vibrating their vocal cords, lips, and nostrils. 14 15
Glossary compression wave pitch vibration the wavelike movement of particles squeezing together and spreading out again how high or low a sound is the back-and-forth movement of matter What did you learn? 1. How is sound made? 2. Describe the two ways stringed instruments are played. 3. Explain how your ears help you hear. 4. In this book you have read about vocal cords and the pitch of your voice. Write to explain how their relationship works. Use details from the book. 5. Compare and Contrast How do people make sounds? How do animals make sounds? Compare and contrast the ways people and animals make sounds. 16