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, the 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, the 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 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, 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!
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 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 e-mail to kids@thescishow.com,
or leave us a comment down below.
We’d like to thank Google Making Science for helping us to make this episode, and thank
you for watching. And we’ll see you next time, here at the fort!