Januari 19, 2017
squeaks, can you hear me? what about now? can you hear me? have you ever noticed that it’s harder tohear people when they’re farther away? the sound of their voice gets harder and harderto hear until eventually ... you can’t hear them at all! but there’s a way to talk to your friendfrom several meters or yards away, without yelling! and, you can make it yourself! before we start building, though, let’stalk about how sound works. all noises, whether it’s piano music,birds singing, or me talking, are made by
vibrations. vibrations are made when something moves backand forth. when things vibrate to make sound, they’re usually so small, and are moving so fast, that you can’t even see anything movingat all. but you can probably feel it! hold your hand up to your throat and say your name. jessi. jessi. can you feel that sort of buzzing in your neck? that’s a vibration, the start of the soundof your voice! what’s vibrating here? it’s two littlethings in your throat called your vocal cords. you can also feel, and see, the startof a sound when you strum a guitar. can you
see the string of the guitar moving reallyfast? that’s a sound just getting started! now, after something like a vocal cord ora guitar string moves, it makes the air move, too! and we know that air is made up of very tiny particles. and these particles end up carrying the vibrations through the air, so sound cantravel! for example, when a guitar string moves, theparticles in the air around the string start to move, too. and then they bump into other particles, making those move. these particles carry the vibrations through the air, until it hits your ear, and you can
hear the music! but the problem is, the vibration starts togo away pretty quickly. after traveling through the air for a bit,the particles don’t bump into each other as hard, and eventually the vibration stops. and if that happens before the vibration makesit to your ears, you don’t hear anything! so now we know that vibrations can make the air move to produce sound. do you think that they can make other stuff move, too? let’s try it out! you’ll need a grown-up...
...two paper or plastic cups… ...a bit of tape… ...a sharp pencil or a pair of scissors… ….and a long piece of string, say3 to 9 meters long. use the scissors to poke holes in the bottomof each cup. now, thread the string through each hole,so that the cups are facing away from each other. if you can, tie a knot at the end of eachstring inside the cup. you can put a little bit of tape on the string, too, just to make sure it doesn’t come out.
now give one of the cups to a friend, andtake one for yourself. walk away from each other slowly until the string is in astraight line between the two cups. and this is important, make sure the string is tight! now tell your friend to put their cup over their ear while you talk into your cup. can your friend hear you? now try putting the cup over your ear, andgive your friend a turn to talk. can you hear them? pretty cool huh?! are the cup and string helping us hear? let’s do a test. if you keep your voiceat the same level and try to talk to your
friend without the cups, can they hear you? well, yes, but not as well! so, what’s going on here? when you use the string phone, your voicemakes the air particles in the cup start to vibrate. these vibrations then make the bottom of thecup vibrate, and make the string move in the same way. and then, the vibrating string makes the bottom of the other cup move. and the particles in the air in that cup, until it reaches your friend’s ear! ok, let’s try another experiment. stand a little closer to your friend so that the string hangs
loose between the cups. can you hear your friend? no -- that’s not working well at all. what’s going on? when the string is loose, it can’t vibratenearly as well. which means, sound can’t travel through it. to see what i mean, ask your friend to move farther away again, so that the string is pulled tight. now, pluck the string with your finger. can you see the string move back and forth? now stand a little closer together again,so the string is loose, and pluck it again.
the string moves a little, but it doesn't keep vibrating. the string has to be tight for your phoneto work, so vibrations can travel through it. keep trying experiments with your string phone. how long can you make the string before the sound goes away? and let us know how it goes. just grab a grown up and send us an e-mail to kids@thescishow.com, or leave us a comment down below. we’d like to thank google making sciencefor helping us to make this episode, and thank you for watching. and we’ll see you next time,here at the fort!
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