(Intro)

Squeaks, can you hear me? What about now? Can you hear me?

Have you ever noticed that it's harder to hear people when they're farther away? The sound of their voice gets harder and harder to hear until eventually... you can't hear them at all!

But there's a way to talk to your friend from several meters or yards away, without yelling! And, you can make it yourself!

Before we start building, though, let's talk 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 back and forth. When things vibrate to make sound, they're usually so small, and are moving so fast, that you can't even see anything moving at 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. That start of the sound of your voice.

What's vibrating here? It's two little things in your throat called your vocal cords. You can also feel and see the start of a sound when you strum a guitar. Can you see the string of the guitar moving really fast? That's a sound, just getting started.

Now, after something like a vocal cord or a 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 can travel.

For example, when a guitar string moves, the particles 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 that vibration starts to go 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 makes it to your ears, you don't hear anything.

So, now we know 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, 2 paper or plastic cups, a bit of tape, a sharp pencil or a pair of scissors, and a long piece of string, say 3 to 9 meters long.

Use the scissors to poke holes in the bottom of 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 each string 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, and take one for yourself. Walk away from each other slowly,  until the string is in a straight 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, and give 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 voice at 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 voice makes the air particles in the cup start to vibrate. These vibrations then make the bottom of the cup 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.

Okay, 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 vibrate nearly 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 phone to 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 email to kids@thescishow.com. Or leave us a comment down below.

We'd like to thank Google Making Science for helping us make this episode! And thank you for watching! And we'll see you next time, here at the Fort!

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