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Physics for Kids4 chapters | 67 lessons
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Suzanne has taught all levels PK-graduate school and has a PhD in Instructional Systems Design. She currently teachers literacy courses to preservice and inservice teachers.
Have you ever noticed that your voice sounds different when you're in a large, empty room? Especially if there isn't a rug or curtains, your voice will usually sound louder. This is because sound travels in waves; the sound waves you make when you speak are traveling through the air in the room, so the room affects what you hear.
Have you ever bounced a basketball? If you bounce it on a hard floor or on cement, the ball bounces very well, but if you try to bounce it in the grass or a rug, it doesn't bounce very well, does it? Like a basketball, sound waves can also bounce.
Sound waves will bounce off hard surfaces, like walls and floors. If the sound waves hit soft things, like carpets, curtains, pillows, plants, or people, the waves are absorbed by the soft things, so they don't bounce off them. So if a room is very empty, the waves will bounce off the walls and floors instead of getting absorbed by the stuff that would normally be in the room, making your voice sound louder.
Sometimes when sound waves bounce off of a hard surface, you will hear the sound repeated again. For example, you might say ''Hello,'' and then a few seconds later, you hear the word ''Hello'' again. This called an echo. The sound waves left your mouth, traveled through the air, hit a hard surface, such as a wall, and then bounced back again, causing you to hear the sound again.
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Have you ever wondered why you don't hear echoes for every sound that is made? The sound waves are typically absorbed before they hit something hard that they can bounce off of. But sometimes there still isn't an echo, even if you're in a place where there are no soft things to absorb the sound waves. Let's see if we can figure out why that happens.
Remember, sound travels through the air in waves. It takes time for those waves to reach a wall or other hard surface, bounce off the wall, and then travel back to your ears so that you can hear the echo. If you are standing close to the wall, the sound will bounce back faster than if you are standing further away.
When you hear a sound, it's held in your memory for only a very short time - about one-tenth of a second. If the sound is able to hit the wall and bounce back to your ears in less than one-tenth of a second, you don't hear an echo! This is because your memory is still holding the original sound and it combines the original sound with the sound waves that bounce back. The sound you hear sounds a bit unusual, but you don't hear two separate sounds as you would if you heard an echo. When the two sounds combine in your memory, it's called a reverberation.
In order for you to hear an echo, you have to be at least 17 meters, or about 56 feet, away from the wall that will be reflecting the sound back to you. That way, it will take the reflected sound more than one-tenth of a second to reach you, so you'll hear both the original sound and the reflected sound separately, as an echo. This is why you may not hear an echo in most empty rooms, but you'll probably hear one if you shout into a canyon.
Sound travels in sound waves through the air. When sound waves hit hard surfaces, they may be reflected back as an echo if you're far enough from the hard surface that reflected the sound. If you're not far enough away, instead of hearing an echo, you'll hear reverberation, in which both the original sound and the reflected sound are combined into one sound.
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Physics for Kids4 chapters | 67 lessons
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