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Welcome to brain Stuff from 10 00:00:26,640 --> 00:00:37,319 Speaker 1: how Stuff works dot com where smart happens. I am 11 00:00:37,320 --> 00:00:40,920 Speaker 1: Marshall brand with today's question. Can two cans and a 12 00:00:41,080 --> 00:00:44,760 Speaker 1: string really be used to talk over a distance? The 13 00:00:44,800 --> 00:00:47,800 Speaker 1: old two cans and a string technique that you see 14 00:00:47,840 --> 00:00:51,440 Speaker 1: in cartoons really does work. The key is to make 15 00:00:51,479 --> 00:00:54,400 Speaker 1: sure that the string is tight between the two cans, 16 00:00:54,800 --> 00:00:58,080 Speaker 1: and this normally means that the distance is limited and 17 00:00:58,240 --> 00:01:00,600 Speaker 1: the two people have to be connected each other by 18 00:01:00,640 --> 00:01:03,720 Speaker 1: a straight line. But as long as the string is tight, 19 00:01:03,840 --> 00:01:06,800 Speaker 1: it does work. It's also a great way to understand 20 00:01:06,800 --> 00:01:11,680 Speaker 1: how telephones work. To try this technique, take two large 21 00:01:11,800 --> 00:01:14,800 Speaker 1: cans or paper cups and punch a small hole in 22 00:01:14,840 --> 00:01:17,400 Speaker 1: the center of the bottom of each with a sewing 23 00:01:17,480 --> 00:01:21,640 Speaker 1: needle or something similar. Take a piece of non stretchable 24 00:01:21,760 --> 00:01:24,840 Speaker 1: thread or kite string about a hundred feet long, and 25 00:01:25,000 --> 00:01:29,280 Speaker 1: thread each end through each hole. Either not or tape 26 00:01:29,360 --> 00:01:31,480 Speaker 1: the strings so it cannot go back through the hole 27 00:01:31,520 --> 00:01:35,120 Speaker 1: when the string is stretched. Now with two people, have 28 00:01:35,280 --> 00:01:37,920 Speaker 1: each one take one of the cups and spread apart 29 00:01:38,000 --> 00:01:41,000 Speaker 1: until the string is tight. If one of you talks 30 00:01:41,000 --> 00:01:43,959 Speaker 1: into one of the cups while the other listens, the 31 00:01:44,080 --> 00:01:46,759 Speaker 1: second person should be able to hear what the first 32 00:01:46,800 --> 00:01:51,560 Speaker 1: person says. Here's why it works. When one person talks 33 00:01:51,600 --> 00:01:54,200 Speaker 1: into his or her cup, the bottom of the cup 34 00:01:54,320 --> 00:01:57,920 Speaker 1: vibrates back and forth with the sound waves. Imagine the 35 00:01:57,920 --> 00:02:00,680 Speaker 1: bottom of the cup moving back and forth very quickly 36 00:02:01,200 --> 00:02:05,000 Speaker 1: thousand times per second or more with the sound waves 37 00:02:05,080 --> 00:02:09,160 Speaker 1: of the speaker's voice. The vibrations travel through the string 38 00:02:09,280 --> 00:02:13,280 Speaker 1: by pulling the string back and forth. Therefore, the bottom 39 00:02:13,280 --> 00:02:16,240 Speaker 1: of the second cup should start to vibrate back and forth, 40 00:02:16,400 --> 00:02:18,800 Speaker 1: just like the bottom of the first cup is vibrating, 41 00:02:19,120 --> 00:02:22,920 Speaker 1: producing sound waves. The second person can hear the sound 42 00:02:23,000 --> 00:02:26,400 Speaker 1: waves and can therefore hear what the first person says, 43 00:02:26,440 --> 00:02:29,480 Speaker 1: this is not much different from how a telephone works, 44 00:02:29,520 --> 00:02:33,160 Speaker 1: except that electric current replaces the string and the telephone. 45 00:02:33,600 --> 00:02:37,799 Speaker 1: In an old style telephone, the person speaking vibrates a 46 00:02:37,919 --> 00:02:45,079 Speaker 1: metal diaphragm. The diaphragm's vibrations rapidly compressed and uncompressed carbon granules, 47 00:02:45,480 --> 00:02:50,280 Speaker 1: changing their resistance. A current passes through the granules, and 48 00:02:50,360 --> 00:02:54,840 Speaker 1: it's strengthened or lessened by the changing resistance. At the 49 00:02:54,880 --> 00:02:58,440 Speaker 1: other end, the rapidly changing current runs through a speaker 50 00:02:58,880 --> 00:03:02,760 Speaker 1: and causes it's diaphragm to vibrate back and forth. So 51 00:03:02,840 --> 00:03:07,400 Speaker 1: the second person here's the first person speaking. Whether you're 52 00:03:07,520 --> 00:03:10,440 Speaker 1: using strings or current, you can see that the same 53 00:03:10,480 --> 00:03:14,640 Speaker 1: basic idea is at work. A voice is vibrating something 54 00:03:14,680 --> 00:03:17,600 Speaker 1: at one end, and at the other end, something else 55 00:03:17,760 --> 00:03:20,320 Speaker 1: is made to vibrate in the same way so that 56 00:03:20,400 --> 00:03:23,480 Speaker 1: the second person can hear what the first person is saying. 57 00:03:24,800 --> 00:03:27,679 Speaker 1: Do you have any ideas or suggestions for this podcast? 58 00:03:28,080 --> 00:03:30,720 Speaker 1: If so, please send me an email at podcast at 59 00:03:30,760 --> 00:03:33,480 Speaker 1: how stuff works dot com. 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