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Sound and Air
by Jeanette Cain
Your world is full of different sounds from the buzzing of a fly, the ticking of a watch, to the screaming siren or the ringing of the telephone. Although they made sound different, all sounds have some likenesses. Sound is caused by a rapid back and forth movement called a vibration. When this vibration occurs, sound waves are sent into the air.
What does your sense of touch tell you about sound? If you put your fingers and hand on a radio that is playing, you can feel this vibration. Can you think of any playing instruments that make a vibration? One may be a guitar. How many others can you think of?
What happens when you talk, or when you speak? The first thing is that you create vibrations in the air with your vocal chords. Do you know how a fish makes sounds? A fish makes sound by forcing air out of their swim bladders. Do you hear the hum of a mosquito? The mosquito makes this hum by the rapid moving of its wings, which is more than 100 times a second!
Does a piano vibrate when someone plays it? If you play the piano, then each time you press a key, a hammer hits a piano wire and this makes it vibrate very quickly. When the wire moves back and forth, the air molecules in the area are given a push. They move just a tiny bit before bouncing back, but because of this they push their neighbors air molecules, too! Those neighbors then move back and forth and push their neighbors and this keeps going on down the line. Did you know that you have air molecules close to your ear? Sooner or later the air molecules close to your ear will push against your eardrum and cause it to vibrate. What do you think happens next? Yes, that's right! These vibrations travel down the nerves that go to your brain and then you can hear the sound!
Sound is not like light, other than having waves. Sound cannot travel through a vacuum, or through the emptiness of outer space. In outer space, sound would need something to carry it. The scientist Robert Boyle discovered this in 1660. He made an experiment by placing his watch in a jar and then he pumped the air out. When he listened to the jar, he could not hear any sound coming from his watch. If you and a friend were on the moon and tried to talk to each other, you couldn't hear. Unless, you took along a walkie-talkie! Just for fun, ask your parents or friends to help you prove whether Robert Boyle's experiment was right or wrong.
Definitions
1. vacuum: an empty space which does not have air in it, or a space which has almost all the air removed.
Sources:
Barnhart, Clarence L. Thorndike-Barnhart Comprehensive Desk Dictionary Doubleday & Company,
Inc: NY. 1965
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