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Speaker 1: dot com slash brain Stuff. Welcome to brain Stuff from
Speaker 1: how Stuff works dot com where smart happens. I am
Speaker 1: Marshall brand with today's question. Can two cans and a
Speaker 1: string really be used to talk over a distance? The
Speaker 1: old two cans and a string technique that you see
Speaker 1: in cartoons really does work. The key is to make
Speaker 1: sure that the string is tight between the two cans,
Speaker 1: and this normally means that the distance is limited and
Speaker 1: the two people have to be connected each other by
Speaker 1: a straight line. But as long as the string is tight,
Speaker 1: it does work. It's also a great way to understand
Speaker 1: how telephones work. To try this technique, take two large
Speaker 1: cans or paper cups and punch a small hole in
Speaker 1: the center of the bottom of each with a sewing
Speaker 1: needle or something similar. Take a piece of non stretchable
Speaker 1: thread or kite string about a hundred feet long, and
Speaker 1: thread each end through each hole. Either not or tape
Speaker 1: the strings so it cannot go back through the hole
Speaker 1: when the string is stretched. Now with two people, have
Speaker 1: each one take one of the cups and spread apart
Speaker 1: until the string is tight. If one of you talks
Speaker 1: into one of the cups while the other listens, the
Speaker 1: second person should be able to hear what the first
Speaker 1: person says. Here's why it works. When one person talks
Speaker 1: into his or her cup, the bottom of the cup
Speaker 1: vibrates back and forth with the sound waves. Imagine the
Speaker 1: bottom of the cup moving back and forth very quickly
Speaker 1: thousand times per second or more with the sound waves
Speaker 1: of the speaker's voice. The vibrations travel through the string
Speaker 1: by pulling the string back and forth. Therefore, the bottom
Speaker 1: of the second cup should start to vibrate back and forth,
Speaker 1: just like the bottom of the first cup is vibrating,
Speaker 1: producing sound waves. The second person can hear the sound
Speaker 1: waves and can therefore hear what the first person says,
Speaker 1: this is not much different from how a telephone works,
Speaker 1: except that electric current replaces the string and the telephone.
Speaker 1: In an old style telephone, the person speaking vibrates a
Speaker 1: metal diaphragm. The diaphragm's vibrations rapidly compressed and uncompressed carbon granules,
Speaker 1: changing their resistance. A current passes through the granules, and
Speaker 1: it's strengthened or lessened by the changing resistance. At the
Speaker 1: other end, the rapidly changing current runs through a speaker
Speaker 1: and causes it's diaphragm to vibrate back and forth. So
Speaker 1: the second person here's the first person speaking. Whether you're
Speaker 1: using strings or current, you can see that the same
Speaker 1: basic idea is at work. A voice is vibrating something
Speaker 1: at one end, and at the other end, something else
Speaker 1: is made to vibrate in the same way so that
Speaker 1: the second person can hear what the first person is saying.
Speaker 1: Do you have any ideas or suggestions for this podcast?
Speaker 1: If so, please send me an email at podcast at
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