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Traveling with Sound
by Jeanette Cain
Sound can travel through water and solids even better than air. Do you remember scenes from the Old Western movies when the train robbers laid their ear to the rails of the track to know when the
train would be getting close? The reason - the rails brought the sound quicker than did the air. Have you noticed in the old movies that an Indian scout would listen for hoof beats of distant
horses by laying his ear to the ground? Maybe, when you've been boating, you have noticed that a boat's outboard motor sounds much louder to you when swimming underwater rather than when your
head is above water. Why not try this this experiment? You will need a friend to help. Find a log, you go to one end of the log and send your friend to the opposite end. Ask your friend to take a
pin and begin scratching at that end of the log. What can you hear? You may also try this with a water pipe in a basement.
You need to make certain that you always have an adult to help with these activities.
Try lightly tapping a spoon on a basement water pipe. Ask your friend to stay on the upper level of the house and to tell you if they hear any sounds. What did you discover?
Sound is similar to light since it travels in waves. Sound travels much slower compared to light, which travels at 186,000 miles per second. Whatever we see is also happening at almost the same
instant in which we see it. Sound travels about 1100 feet per second and because of this slowness, you can hear a carpenter hammering a nail far in the distant but you will need to wait for it to
reach you. Thomas Edison was deaf, so how did he hear his phonograph? He invented the phonograph by feeling the vibrations through his teeth! Some people who have lost their hearing
actually feel the vibrations through the bones of their skull.
Have you watched thunderstorms? A thunderstorm produces lighting and thunder at the same time, but you will see the lightning before you hear the thunder. You probably know that you can
figure out how far away lightning is by counting the number of seconds between the time you see the flash and the time it takes you to hear the thunder. It usually takes about five seconds for
sound to travel one mile, so if you count to ten between the lightning flash and the time you hear the thunder you will know that the lightning was about two miles away.
Science is always discovering new ways in which to use sound. Some believe that one day a home may have an ultrasonic washer and dishwasher that can clean dishes and clothes using only sound. Can
you think of ways that sound may be used to help doctors, engineers, architects and others?
Source:
Editors. The World Book Encyclopedia. World Book-Childcraft International, Inc: Chicago. 1990
Further Study:
Lessons on Waves, Light, and Sound
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