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This is Blue Peter, but mini.
Expect epic adventures, makes, bakes,
presenters and your host.
We've only got five minutes, so get ready for your Blue Peter adventure.
It's time to welcome back to Blue Peter Mr Greg Foot.
-Yes, Greg. What have you got for us today?
-I'm so excited.
-Right, I want to bring the weather from outdoors,
-I want to make cloud and rain right here,
in the Blue Peter studio.
I definitely want to see that, as well.
-Let's start with the cloud. So, I'm going to make you
a little cloud and then we are going to super-size it.
So, first of all, question for you - what is a cloud made of?
-Good man, yeah, water.
But the real question is how does that water clump together
-into a cloud and how does it say up there?
So, all around us is air and that's made of a whole bunch of different
gases. You've got oxygen that you breathe in,
you've got carbon dioxide that you breathe out, a whole host of others.
-Including water, but as a gas we call it water vapour.
Now, as all that gas rises, as that water vapour rises,
it cools down when it gets to the top of the atmosphere.
And when it cools down enough, it can actually turn from a gas
into a liquid. If you think about when you breathe
on a really cold window...
So that the water vapour, gas in your breath, cools down
-into little droplets that you see.
-It's called condensation.
That's all a cloud is, just condensed water vapour.
-Now, can you start pumping water?
-Some eye protection
-for you first.
-Thank you. Remember, safety never takes a day off
-on Blue Peter.
-True, that. Right, 15 pumps, please.
So, what you're doing right now is you're pumping air
into the bottle, OK? And the air has got water vapour in it.
I've put a little bit of water in there, as well. So, you're building
up the pressure. When the pressure is enough, I'm going to pop
the top off, the pressure is suddenly going to decrease, which
cools the whole thing down. So, it's going to be like what happens
up in the atmosphere. It cools down and, hopefully, we'll get a cloud.
So, what it needs to do is, it needs to have something to grip hold of.
All those water droplets need to grip onto something. Up there,
in the sky, it could be salt from the sea. It could be dust,
it could be soot from a wildfire. So, I put a little bit
of soot in here, very carefully, earlier. Right, are you ready?
-Yes, I am.
-Three, two, one...
-Yes, look at that!
-You see that cloud in there?
-There's a cloud in the bottle!
-That is it. There's probably millions
of little, tiny water droplets in there to make our cloud.
-So, I'm going to make a much bigger version,
-to fill the whole studio afterwards.
-The question, I guess, is how it actually stays up there.
And it's because the droplets are so, so tiny. They're so small,
they're surrounded by air. They're light enough to float up there,
but, once they start banging together and the cloud grows,
the droplets get so big that they can start to fall. And that,
-of course, is...
-Rain. Question for you, Radzi,
-from Blue Peter.
-What shape is a raindrop?
-That easy, so, it's like
a teardrop. So, it's a bit like that.
HE IMITATES BUZZER
I'm going to show you. Right, this is a raindrop levitation device,
-that I built earlier.
-You're going to love this.
We, obviously, can't skydive next to a raindrop to see its shape.
So, what this is going to do is, air's going to rush up
and I'm going to try to keep a raindrop in place. So, air's
going to be rushing around it. It's exactly the same
-as what happens as it falls.
-So, let's give this a go.
-My air is on.
-Yeah, I can hear that.
-Now, what I'm going to try to do is
-I'm going to put a raindrop in there.
-There we go!
-There we go!
-Now, that's not bad, very hard to do live.
-So, what did is I filmed it in slow-motion,
-earlier in the rehearsal.
-Have a look and tell me
-what the shape is.
-Watch this, this is amazing, watch.
-Out it comes.
-OK, it goes down.
-Oh, it's really flat.
-It is flat underneath.
-Look at that there!
-How gorgeous is that?
-This, Radz, this is my favourite fact, right.
-OK, hit me.
-You'd think a raindrop is round, spherical, like a ball.
When they're really, really small, they are that shape,
but when they get bigger, they fall.
And they fall fast, like 15mph, 20mph.
They're falling and all that air is hitting them underneath
and it squashes the bottom of the raindrop
-and you get that beautiful burger-bun shape.
Why you said teardrop is you always see it running down a window, yeah?
Or dripping out of a tap.
What that does is it pulls some of it behind it and it creates
-this tail. There you go.
-So, there you go, it's all a big myth.
Now, Greg, I hate to hurry you, but I want to see the big one.
Let's do it. Right, come over here, my friend.
What you're going to need is to put on this poncho, because this
-could get a little bit damp.
-Thank you, sir.
a cloud is just trillions of drops of water vapour that have condensed,
-that have cooled down into water droplets.
can you bring on my ingredients for a cloud, please, mate?
-Tom, come out, my friend.
-Yes. What's in this?
So, in this is everything we need to make a cloud. Thanks, buddy.
So, what we're going to do here is we've made ourselves nice and safe.
-Nice and safe, like this.
-Now, we need something very, very cold,
right? Because when it's up there in the cloud,
that's what causes a cloud to condense, to cool down.
So, what I've got here is liquid nitrogen.
Whilst you're pouring that, I do have to say, please,
for goodness' sake, do not try this at home. That's why we've got masks.
-Greg knows exactly what he's doing.
-So, there, we've got some
liquid nitrogen. Now, what I've also got is some hot water.
-Even that looks cool.
-The hot water is going to go into
my liquid nitrogen, it's going to turn it from a liquid into a gas.
-Pull the gas up in the air, that's going to cool down
all the water vapour in the sky and make a cloud.
-I want to see this.
-Are we ready for this cloud?
-Everyone on the floor happy?
OK, so, in three, two, one...
Oh, my goodness!
-We've just made a cloud on Blue Peter!
-Can we see that again?
-Look at the replay of that!
-That's in slow motion, look at that!
-Oh, that looks good.
So, there it is, our cloud. Just all those water droplets in the air.
Join in every Thursday on CBBC.