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This is Blue Peter but mini!
Expect epic adventures,
presenters and your post.
We've only got five minutes so get ready for your Blue Peter adventure.
-This is one of my favourite experiments...
-You look excited.
-..because this combines music and fire.
Firstly, let's have a look at the piano.
-Linds, you play the piano, right?
-Just give us a tinkle of the old ivories there.
-So, just anything?
Now, if you just hit one note for me, just one key. That's it, yes.
So what's happening is you're actually moving a lever inside
and it's causing this little hammer here to hit against the string.
-And that causes that string to wiggle,
it causes it to vibrate and it wiggles,
it vibrates the air around it as well
and that then vibrates the air molecules next to that
and the ones next to that, all the way to your ear.
Wow, that's how we hear it?
-Yeah, if you think about dropping a stone into a pond.
You drop it in and then you get ripples coming out,
all those water molecules are vibrating the ones next to it.
You get a wave.
Sound is exactly the same but it's a wave in air, not water.
-So how exactly do you hear that wave though?
How does it travel into your ear?
So it comes towards your ear, that wave of sound,
and it gets funnelled down into your ear canal here
-and then it hits your eardrum, which I can pull out - ugh!
It sets your eardrum vibrating as well
and then your eardrum actually vibrates all these little bones
next to it and causes some fluid in your inner ear to vibrate
and that sends a signal to your brain.
So it's all about
that sound is a wave and it's a series of vibrations.
-Every time we hear something all of that goes on?
-But I want to actually have a look at some sound.
I know what you're thinking, "Greg, hang on a minute.
"Sound travels through air, you've just said that,
-"but air is invisible. How are we going to see this?"
Well, I don't want to put it through air, I want to put it through gas.
-I love it.
I'll never get bored of that but please don't try this at home,
-for goodness' sake, stay safe.
So, this is known as a Rubens' tube
and at the end here I've got a speaker, and the speaker's
-attached to a microphone that I've put inside the piano.
-So just give us a few notes, a few chords.
-Yeah. You can see it's dancing around.
So what's happening is the speaker is vibrating back and forth
and it's setting off those vibrations, a sound wave,
all the way through the tube, but I've been clever,
I've blocked the tube at the other end
so the waves actually bounce back and they mix up inside the tube.
Now, if we hit the perfect note on the piano we're going to be able to
-freeze that sound wave made of fire in midair.
-So that's what we're going to try.
-This is ridiculous, let's do it.
So give us a low note if you can, please.
-Let's start with a low note.
-There we go.
-Yeah, that's good. Lovely.
Now what you can see is we've actually got a peak and a trough
and a peak and a trough and a peak
so we've got a wave kind of frozen in midair. Remember that one.
-Now go to a higher note, jump right up.
So you get a peak and a peak and a peak and a peak
so now the waves are a lot smaller, they're like that compared to
being like that, like they were before, and this is all sound is.
Music is just a series of waves. Big, long waves - a low note.
Short, little waves are high notes, easy as that.
There's actually something I've seen that's pretty cool
and it's where you can use sound to actually break glass.
-Can I put you on the spot?
-Just a bit!
-OK, so this is theoretically possible, right?
-It can happen.
-But it is so, so hard to try.
-Especially on a live show.
-But I thought, why not try it?
-Do it anyway. It's Blue Peter, isn't it?
So what we need is a singer, a singer who can sing really,
-We can do that.
And hit a note and keep that note really perfect.
-OK, well, that rules us out.
-We can't do that, can we?
So I think we should welcome in a scientific singer, it's Helen.
-Welcome to the show.
Thank you for coming on Blue Peter today.
-Absolute pleasure to sing for science.
-So here's the thing.
If Helen was to sing actually at the glass like this,
it could smash and that's dangerous so what I've done is I've set up
a speaker here and I've put the glass above the speaker.
So Helen's voice is going to go into that microphone,
it's going to travel through to the speaker, speaker's going to vibrate,
it's going to make the air vibrate
and it's going to set the glass vibrating.
-But she can't just hit it with any old note, right?
This is the note that she's trying to go for.
-If you flick a glass very carefully...
That is the note that a glass likes to vibrate with.
Don't try that at home, OK? It's proper dangerous.
You can flick a glass, you get a perfect note,
we call that its natural frequency.
Now, I've actually flicked this glass earlier and worked out
that note that you need to hit this with and this is that note.
-Now, I've put a ping- pong ball inside and that shows you
when the glass is vibrating.
The ball won't smash the glass, all right?
It's Helen's voice that's going to smash the glass. So, guys...
-Helen, do you think you can do this?
-It's live, you get one chance.
-I'm ready, is the glass ready?
-Yes, I like that answer.
-Ear protection, eye protection, guys.
-Helen's all set as well.
We should say one more time - do not try this at home.
Helen is a pro, as is Greg, so please don't do this at home.
-Right, here we go.
-So, Helen, here's your tone.
NOTE PLAYS, HELEN HUMS
# Ah... #
-My goodness, Helen!
-You legend. Awesome!
That was amazing, Helen, well done!
-That is the power of sound.
Join in every Thursday on CBBC.