Sound is produced when an object vibrates, creating a pressure wave. This pressure wave causes particles in the surrounding medium (air, water, or solid) to have vibrational motion. As the particles vibrate, they move nearby particles, transmitting the sound further through the medium.
1. How Sound Travels by Cindy Grigg
2. Answer the following questions BEFORE you read this book. It is okay if you do not know as much as you thought. Do the best you can! :KDWFDXVHVVRXQGV" +RZGRZHKHDUVRXQG" You have planned a relaxing day at the beach. You swim all morning, and then you lie down in the warm sun and close your eyes. Aah, how peaceful! The sound of the waves gently lapping at the sand lulls you to sleep. +RZORXGLVWRRORXG" Then, a jet ski roars by. 1 2 How Sound Travels
3. A lifeguard blows his whistle. Sound is all around us. What is sound? How does sound travel? All sounds are created by vibrations. An object vibrates, which sets up a sound wave, which travels through a medium (such as air), And about a million birds fly in to find some lunch, until it reaches your ears. screeching and squawking loudly. There goes your 3 4 How Sound Travels
4. The sound of a person talking is produced in the person's larynx (LAR-ingks), which is in the throat. Stretched across the larynx are thin folds of tissue called vocal cords. When a person is not talking, the vocal cords are relaxed. A larger opening lets more air pass in and out of the lungs. When a person speaks, the vocal cords are stretched tightly Many things cause vibrations and sounds. over the opening. Air from the lungs rushes Dolphins make vibrations to produce through the small slit between the taut vocal clicking and whistling sounds by using air cords, and they begin to vibrate. filled pouches connected to the blowholes on top of their heads. The wings of flies, bees, and other insects vibrate to make buzzing sounds. 5 6 How Sound Travels
5. Vibrations travel out through the air in all directions. When they reach you, your outer ear funnels them inside the ear canal, and they cause your eardrum to vibrate. Those vibrations reach the tiny bones in your middle ear, which amplify them. The Sound can also be caused by an action, such stronger vibrations reach the cochlea, which as a tree crashing down or a plate hitting the is filled with liquid. A wave moves through floor. The movement causes the vibration of the liquid inside the cochlea. Sensitive hair air molecules. cells move up and down with the wave. The vibrations are changed into electrical signals. The auditory nerve carries the electrical signals to the brain. Your brain interprets the message as a particular sound. 7 8 How Sound Travels
6. You can make a mechanical wave that is similar to a sound wave using a Slinky toy or a rope. Move both ends of the rope or Slinky Sound waves are mechanical waves. They up and down until you make a smooth wave move through some type of material, called a pattern. medium. Sound can travel through air, water, or any medium. Try listening to music when you're lying in the bathtub with water over your ears. Sound travels even better through solids. You may have heard of Native Americans listening for hoof beats by putting their ears to the ground. You could try putting a drinking glass against the wall to listen to someone talking in another room. 9 10 How Sound Travels
7. Sound waves cannot travel where there is no medium to travel through. That is why there is no sound in outer space. The speed of sound is different traveling through different mediums. Sound travels about four times faster in water than it does in air. But whatever the medium, sound travels much Shine a flashlight at a mirror. What happens? slower than light does. The speed of sound is Light is reflected. Sound waves can be only about 770 mph. The speed of light is reflected, too. We call the reflection of sound about 671,000,000 mph. Sunlight travels the waves an echo. Yelling or any loud noise 93,000,000 miles from the sun to Earth in inside a canyon can cause sound waves to about 8 seconds! reflect off the rock walls of the canyon and travel back to our ears. We hear the echo. 11 12 How Sound Travels
8. Because the speed of sound is slower than the speed of light, thunder happens after Sound is a form of energy. A decibel (dB) lightning. You can count the seconds is the unit of measure. A decibel meter is between lightning and thunder to tell how far used to measure sound. away the storm is. Every five seconds equals one mile. If you count ten seconds, for Normal talking has a loudness of about sixty example, it means that the storm is two miles dB. Any sound above eighty-five dB can away. cause hearing loss. The loss is related to both the intensity of the sound as well as the length of exposure. You know that you are listening to an eighty-five dB sound if you have to raise your voice to be heard by somebody else. 13 14 How Sound Travels
9. Sound is energy. Sound is caused by vibrations. Sound travels in waves. Sound waves can bend around or bounce off objects. When sound waves Eight hours of listening to ninety dB sound reach our ears, parts inside our ears vibrate, too. can cause damage to your ears. Any Then we can hear sounds. exposure to one hundred forty dB sound will cause immediate damage and causes actual pain to the human ear. 15 16 How Sound Travels
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