WEBVTT - Can cans and string really be used like a telephone?

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<v Speaker 1>dot com slash brain Stuff. Welcome to brain Stuff from

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<v Speaker 1>how Stuff works dot com where smart happens. I am

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<v Speaker 1>Marshall brand with today's question. Can two cans and a

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<v Speaker 1>string really be used to talk over a distance? The

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<v Speaker 1>old two cans and a string technique that you see

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<v Speaker 1>in cartoons really does work. The key is to make

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<v Speaker 1>sure that the string is tight between the two cans,

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<v Speaker 1>and this normally means that the distance is limited and

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<v Speaker 1>the two people have to be connected each other by

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<v Speaker 1>a straight line. But as long as the string is tight,

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<v Speaker 1>it does work. It's also a great way to understand

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<v Speaker 1>how telephones work. To try this technique, take two large

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<v Speaker 1>cans or paper cups and punch a small hole in

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<v Speaker 1>the center of the bottom of each with a sewing

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<v Speaker 1>needle or something similar. Take a piece of non stretchable

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<v Speaker 1>thread or kite string about a hundred feet long, and

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<v Speaker 1>thread each end through each hole. Either not or tape

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<v Speaker 1>the strings so it cannot go back through the hole

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<v Speaker 1>when the string is stretched. Now with two people, have

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<v Speaker 1>each one take one of the cups and spread apart

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<v Speaker 1>until the string is tight. If one of you talks

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<v Speaker 1>into one of the cups while the other listens, the

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<v Speaker 1>second person should be able to hear what the first

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<v Speaker 1>person says. Here's why it works. When one person talks

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<v Speaker 1>into his or her cup, the bottom of the cup

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<v Speaker 1>vibrates back and forth with the sound waves. Imagine the

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<v Speaker 1>bottom of the cup moving back and forth very quickly

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<v Speaker 1>thousand times per second or more with the sound waves

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<v Speaker 1>of the speaker's voice. The vibrations travel through the string

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<v Speaker 1>by pulling the string back and forth. Therefore, the bottom

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<v Speaker 1>of the second cup should start to vibrate back and forth,

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<v Speaker 1>just like the bottom of the first cup is vibrating,

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<v Speaker 1>producing sound waves. The second person can hear the sound

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<v Speaker 1>waves and can therefore hear what the first person says,

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<v Speaker 1>this is not much different from how a telephone works,

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<v Speaker 1>except that electric current replaces the string and the telephone.

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<v Speaker 1>In an old style telephone, the person speaking vibrates a

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<v Speaker 1>metal diaphragm. The diaphragm's vibrations rapidly compressed and uncompressed carbon granules,

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<v Speaker 1>changing their resistance. A current passes through the granules, and

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<v Speaker 1>it's strengthened or lessened by the changing resistance. At the

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<v Speaker 1>other end, the rapidly changing current runs through a speaker

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<v Speaker 1>and causes it's diaphragm to vibrate back and forth. So

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<v Speaker 1>the second person here's the first person speaking. Whether you're

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<v Speaker 1>using strings or current, you can see that the same

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<v Speaker 1>basic idea is at work. A voice is vibrating something

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<v Speaker 1>at one end, and at the other end, something else

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<v Speaker 1>is made to vibrate in the same way so that

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<v Speaker 1>the second person can hear what the first person is saying.

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