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00:30Thank you very much, and welcome to another Think of a Number.
00:40You there. Can you tell me how many sevens in 28?
00:45Four. Four? Absolutely correct.
00:48Slightly harder one here. How many fours in 28?
00:52Seven. Seven? Oh, it's easier than I thought.
00:55Yes. Now, we're living in an age where everything is getting smaller.
00:59When you think about it, you've got micro dots, silicone chips, and transistors,
01:03and we're packing more and more into a smaller and smaller space.
01:07So why not with numbers?
01:09Why does 28 always have to have four sevens?
01:12It's a bit boring, really.
01:13Well, I've got a friend who's got a theory that it might not be actually working out that way.
01:18Ah, yes, that's absolutely right.
01:22You see, the reason is, today you go to school and you're taught that there are four sevens in 28s.
01:27But it could be that that's wrong, in which case you're remembering the right answer for the wrong reason.
01:32And the right answer could be completely different.
01:33I'll show you what I mean.
01:34Now, can we put 28 down there, and divide by seven?
01:39Well, we'll try it.
01:40Seven into two won't go.
01:43Right, seven into eight goes?
01:45One.
01:46Put the one up there, seven down there, take it away.
01:48Seven into 21 goes?
01:50Three.
01:50Three.
01:52So there are seven thirteens in 28.
01:55You don't believe me.
01:56All right, I'll tell you what I'll do.
01:58We'll try it again to check out.
01:59And see what seven times thirteen equals.
02:02Are you ready?
02:02Seven threes are?
02:04And one seven is?
02:06Seven.
02:07Add it together, 28.
02:09You still don't believe me?
02:10All right, I'll tell you what we'll do.
02:12What we'll do is write thirteen down seven times.
02:14Can you count with me?
02:15One, two, three, four, five, six.
02:18Is that right?
02:20Six, yes, seven.
02:21And if we add that up, add with me.
02:22It's three, six, nine, twelve, fifteen, eighteen, twenty-one, two, three, four, five, six, seven, twenty-eight.
02:29You see, it absolutely proves that we've been doing our sums wrong.
02:33And you can get a lot more into a lot more numbers if you know how to pack them in.
02:42Well, this program isn't about doing sums wrong.
02:46But it is about packing things in.
02:48Getting as much in under pressure as we possibly can.
02:51So, we'll start straight away.
02:53Can I have my costume, please?
02:55Thanks very much.
02:55I'll start with a coat.
02:58I'm going to be a bit warm in here, but that doesn't matter, because I'll be talking a lot of hot air later on.
03:02Can you do that up?
03:04I'll also be looking at some very cold facts.
03:08I'm wearing protective clothing, because I need it.
03:10But I should advise people in the audience to wear protective clothing,
03:13because I promise you, before the end of the program, some of them are going to get blown up.
03:18I can have me goggles.
03:19Thanks very much, lads.
03:20Thanks.
03:21So, we're all set.
03:24On we go intrepidly, for a breath of fresh air.
03:27Now, what I've done is breathe some of this stuff in here, and it makes me talk much quicker,
03:42because I'm very high-pitched, so I can get a lot more into the program by talking very fast.
03:45You see, all the program will condense.
03:46Ah, I'm going back to normal now.
03:48It's going back to normal.
03:50And I'm normal.
03:51What I've been breathing there is oxygen and helium mix.
03:54And this is the mixture that divers use at the bottom of the sea, because the pressure is very great.
03:59So, they need pressure in their lungs to equalise the pressure of the water.
04:03So, they breathe oxygen under pressure and helium to fill in the gap.
04:08Now, the only effect helium has is it makes you talk squeakily, and it also feels rather cold.
04:14But nearly all gases are much colder than air.
04:18And the colder a gas becomes, well, if it gets cold enough, it turns to a liquid, just as steam turns to water when it cools down.
04:26However, gases need to get to very low temperatures to turn to liquids.
04:32And when they do, they take up a space about one six hundredth of the volume they started out at as a gas.
04:39So, in liquid form, gases are easy to transport.
04:43So, to that end, a whole science of low temperatures has been built up.
04:48The science of cryogenics.
04:50This is liquid nitrogen.
04:58Now, liquid nitrogen freezes at minus 210 degrees centigrade.
05:02But it boils at minus 193 degrees centigrade.
05:06And it's at about that temperature now.
05:09Now, you can't measure that temperature with a mercury thermometer.
05:12Because this is what happens to mercury when you put it in liquid nitrogen.
05:20It's absolutely solid.
05:24And I've got a six-inch nail here.
05:33And it's almost through the block.
05:36Absolutely solid mercury.
05:38Now, if we put that in warm water...
05:42It boils like mad.
05:47And you can hear it crackling.
05:53And slowly, the mercury comes off in little drops.
06:02And becomes its runny old self again.
06:05I'll leave that there.
06:10Now, this liquid nitrogen...
06:13If I put my finger in, it would freeze absolutely solid.
06:16And it wouldn't thaw out till next Thursday.
06:19However, if we dropped meat in there, or vegetables, or even flowers...
06:25They would freeze.
06:33And in no time at all, be absolutely brittle.
06:36Just like cornflakes.
06:42However, if we let it get back to normal temperature...
06:46The flour would apparently be none the worse for wear.
06:51So if it can preserve things by putting them in liquid nitrogen and freezing them...
06:56Could we do that with people?
06:57Well, it's been found that they can freeze sperm, and eggs, and some insects, and small mammals.
07:07Have been frozen, and then brought back to normal temperatures, and found to be none the worse for wear.
07:13Now, if you could do that with people, you could conquer space.
07:16Because the only way to get to the stars is to travel hundreds, or perhaps thousands of years through space.
07:21So you could put somebody in suspended animation, and warm them up when they get to the other end.
07:26But to get us through space, we need some more liquid gases.
07:29We need liquid oxygen, and we need liquid hydrogen.
07:35This is a model of Saturn V.
08:04The rocket that was built to put man on the moon.
08:07It's 373 feet tall, but the top 80 feet is the actual space module itself.
08:13And the rocket is in three stages.
08:15One, two, and three.
08:18Now, the whole weight of this is about 280 tons.
08:22But the weight at blast-off is 2,700 tons.
08:26Because at blast-off, 90% of the weight is taken up with fuel.
08:3112 million gallons of liquid hydrogen, liquid oxygen, and kerosene.
08:38The fuel is stored in refrigerated tanks in the body of the rocket.
08:43And they're so well insulated that if you left an ice block inside one of the tanks,
08:47it would take eight years for the outside air to get in and melt it.
08:50Now, the power is achieved by mixing the liquid hydrogen or the kerosene with the liquid oxygen
08:57and burning it.
08:59And immediately it turns back into gas, multiplying in volume 600 times
09:03and pushing the gas out at the bottom.
09:07This forces the rocket up into the air
09:10until it accelerates to 25,000 miles an hour.
09:15And at that speed, it overcomes the gravitational pull of the Earth
09:19and sails out into space,
09:21propelled solely by the pressure of hot, expanding gas.
09:27As well as liquid gases, there are some liquids that themselves contain gas.
09:48This is lemonade.
09:49And lemonade contains carbon dioxide, which has been forced in under pressure.
09:54Cheers.
09:54I'm a secret lemonade drinker.
09:58And you've all got lemonade in the audience, haven't you?
10:01So take the tops off, the lemonade.
10:03Don't drink it yet.
10:05Or perhaps just a little bit out of the top, if you like.
10:08You've all got packets.
10:09Open the packet, take the top off,
10:11and you shall find peanuts.
10:13When you've got a peanut,
10:15drop it in your lemonade
10:16and see what happens.
10:20It sinks and then floats.
10:22OK, well, I've got a glass here.
10:25Put that on there.
10:27There's yours.
10:29Now, if you drop a nut in here,
10:32what happens is it sinks
10:34and then comes to the top.
10:39And as it sinks, it gathers bubbles.
10:41The carbon dioxide forms bubbles
10:44and buoys it up like a life jacket and brings it to the top.
10:46So have a go.
10:48See if that works.
10:50Yeah?
10:51Yeah.
10:52Great.
10:53OK.
10:55I'll have that one back.
10:57And could I have four helpers, please?
10:59You four there.
11:01Could you come round here?
11:04That's it.
11:05Leave your things there.
11:05Now, we've got four more bottles of lemonade.
11:08If you open the bottles,
11:09just take the top off.
11:13And leave them there.
11:15And you've each got a bowl of something.
11:18This is salt.
11:20That's talc, talc and powder.
11:22That's flour.
11:22And that's sugar.
11:24So you've got one each.
11:25Get a spoonful of your substance.
11:29Hold it at the top of the bottle.
11:31And when I say go,
11:33pop it in.
11:34Go.
11:39Look at the end two.
11:42They've really bubbled up
11:44because every single grain acts as a catalyst
11:46and brings out the gas.
11:48But the middle two haven't passed their physical.
11:52So let's try stirring them up.
11:55You do it.
11:58That's all it needs.
12:03Isn't that amazing?
12:04And it brings the gas out of the liquid.
12:06Like mad.
12:07Okay, thanks very much.
12:09There you are.
12:09You're all physicists.
12:10Or physiologists.
12:14So that brings the gas out of the substances.
12:17Now, gases are used in many other ways.
12:19Aerosols, for instance,
12:20have got gas which is released
12:21at the press of a button.
12:24That's soap.
12:24But we use gas in many other everyday things
12:28like balloons.
12:31Oh!
12:34Now, although balloons are everyday things
12:36and great fun,
12:37there are lots of balloons that are very important
12:38like weather balloons
12:39and lots of other things
12:40that inflate with compressed air.
12:42Things like...
12:43Oh, my...
12:44More balloons!
12:46Or...
12:47One of these.
12:48Can you grab the other end, someone?
12:50Can you come and grab the other end, please?
12:53And pull it over here.
12:56About there.
12:57Now, do you know what this is?
12:59Well, it's some...
13:00It's...
13:01It's a...
13:02Say that again.
13:03Nice one.
13:04Well, it might be.
13:05Hang on.
13:06It is.
13:06And the thing with the life raft
13:07is you must never pull this.
13:10Look at them, you do!
13:15It inflates very quickly.
13:21Look!
13:23People have been known to survive
13:25for 112 days in the Pacific
13:27in one of these.
13:28So they're absolutely vital.
13:31It's also very rigid.
13:32You can stand all the weather.
13:34And it's very light.
13:36Can a few of you give me a hand
13:37to move it over there.
13:43There they are.
13:43It's as light as air, isn't it?
13:49Thanks very much.
13:50And there's the cover.
13:52That was balloons.
13:53Because I've got something else
13:54over here to show you.
13:55When you walk about in the open air,
14:06you're carrying on your head
14:07a column of air
14:085,000 miles high
14:10weighing about a tonne.
14:12At the top
14:14there's the exosphere
14:15which goes
14:16from about 5,000 miles
14:18down to 450 miles.
14:20Next comes the ionosphere
14:21and that's where
14:23meteorites burn up
14:25so they hardly ever
14:25reach the surface of the earth.
14:27Then
14:28comes the
14:29stratosphere
14:30which contains ozone.
14:32and the ozone
14:33and the ozone protects
14:33from harmful radiation.
14:36Lastly,
14:36the final belt
14:37is the
14:38troposphere
14:38which is the very
14:41bottom belt.
14:42It only goes up to
14:43about 7 to 10 miles deep
14:44but that small band
14:46contains 80%
14:47of the mass
14:48of the atmosphere.
14:50It also
14:51supports
14:52all living things
14:53and it contains
14:5417 million
14:55million tonnes
14:56of water
14:57and that water
14:58together with
14:59the varying pressures
15:00in the atmosphere
15:01create
15:02our weather.
15:07The most violent
15:09of all kinds of weather
15:10is the hurricane.
15:12The hurricane
15:12starts at sea
15:14with hot air
15:15rising in a column
15:16and mushrooming out
15:17and then
15:18as the earth
15:19rotates
15:19it gives it a twist
15:20just like your bath
15:21water's given a twist
15:22and it spirals down
15:23the plug.
15:25Then
15:25you've got
15:26a hurricane.
15:27The outer edge
15:27travelling at about
15:28200 miles an hour
15:29but the centre
15:30absolutely still.
15:33Now
15:33in recent times
15:35we've been able
15:35to put satellites
15:36in the upper atmosphere
15:37so that we can
15:38predict our weather
15:40very accurately
15:41and take precautions
15:42against hurricanes
15:43which is just as well
15:44because it's doubtful
15:45that man will ever tame
15:47the mighty
15:47hurricane.
15:50Oh it's got me
15:50half.
15:51And there
15:52good we have.
15:54Right.
15:55I feel a little
15:55windstruck now.
15:56Have you all got
15:57pieces of wood
15:57in this part of the audience
15:59with a hole in?
16:01I want you to blow
16:02through the hole
16:03holding it down
16:05and the piece of paper
16:07I want you to hold
16:08underneath
16:08right up close
16:09touching
16:10and hold it on
16:12the flat of your hand
16:12piece of paper
16:13blow hard
16:14and when you're blowing
16:15hard
16:15take your hand away.
16:18Anybody done it?
16:18You're not blowing
16:19hard enough
16:20really hard
16:20there's somebody
16:22done it at the back
16:23there
16:23that was very good
16:25what happens is
16:27as you blow
16:28the air fans out
16:29across the cart
16:30and moving air
16:30has got less pressure
16:32underneath
16:32the air is absolutely
16:33still
16:34and the high pressure
16:35holds up the cart
16:36and it's held
16:40on a cushion of air
16:40and that's just how
16:42well hang on a second
16:44hold that
16:45and you two
16:45can you come out
16:46with me
16:46leave those there
16:47you come first
16:49can you think of a number
16:50between one and ten
16:51nine
16:51righto
16:53I want you to
16:54this is a door
16:55doesn't look much like a door
16:56I want you to count
16:58from nine to zero
17:00ready
17:00go
17:01nine
17:03eight
17:04seven
17:05six
17:07five
17:08four
17:09three
17:10two
17:11one
17:13zero
17:14right hand down a bit
17:22it's a hover chair
17:26hang on
17:27it's the chair that's making those noises
17:29not me
17:29right
17:31what it is
17:32is a chair with four pads
17:35and I'll show you the pads
17:37perhaps we can tilt it
17:38up
17:38swing it round a bit
17:41and there they are
17:42four rubber pads
17:44can you turn the air on
17:46just slowly
17:46nice and slowly
17:47more
17:50and you will see the air
17:59blowing out
18:01there it is
18:04okay
18:04turn it off again
18:05now that force
18:07is only about the same force
18:08as a vacuum cleaner
18:11a normal household vacuum cleaner
18:13in fact
18:13Christopher Cockrell
18:14who designed the very first hovercraft
18:16used a vacuum cleaner
18:18in reverse
18:18for his first experiments
18:19would you like a go
18:20sit on
18:21and it's completely frictionless
18:33just get a bit of vibration
18:39onto the pads
18:39would anybody else over here
18:41like a go
18:41you on the end
18:44all right
18:44can you come and help
18:45the two of you
18:46I want you to bend down
18:48and guide this end
18:49no you stay there
18:49in your seat
18:50all right
18:52and guide that end
18:54because out they come
18:55you didn't expect that
19:00did you
19:00a whole section of audience
19:04and you need absolutely
19:05no pressure
19:05to move them
19:08other way
19:12and back you go
19:35coming in to dock
19:37don't worry about the balloons
19:38they'll go
19:39thanks ever so much
19:41give them a round of applause
19:42so there we are
19:47we've seen that just air pressure
19:48can lift one person
19:49or nine people
19:51and with the biggest hovercrafts
19:53air pressure can lift
19:54400 people
19:56and 50 cars
19:58and when you think about it
19:59it's air pressure
20:00that holds up every aircraft
20:01flying around the world
20:02and the gases in the air
20:05also support
20:07not just aircraft
20:08but support
20:09every living thing
20:09oxygen
20:10for humans
20:11and animals
20:12and carbon dioxide
20:13and nitrogen
20:14for plants
20:14so you could say
20:16the air
20:16is a very good friend
20:18because the definition
20:18of a good friend
20:19is someone
20:20who'll support you
20:21especially
20:22under pressure
20:24we've got a trick here
20:26will you help
20:28you'd like to help
20:28ten matches
20:30in each pile
20:31I'm going to turn me back
20:32I'd like you to think
20:32of a number
20:33and take that number
20:34away from each pile
20:35okay
20:36so if you think of three
20:37you take three from
20:38each pile
20:39have you done that?
20:47yes
20:48righto
20:49now
20:49from pile A
20:51take three more
20:52and put them on pile B
20:55you can scrap the rest
21:02of pile A now
21:03from pile C
21:05take three
21:06and put them on pile B
21:08now I want you to count
21:15the number of matches
21:16that are left in pile C
21:17and take that number
21:21away
21:21from pile B
21:23it sounds like
21:25a Jimmy Young recipe
21:26doesn't it?
21:28okay
21:29have you done all that?
21:30yes
21:30now I've got a seesaw here
21:32if I can find it
21:33in my hand
21:33which is very delicate
21:35I want you to
21:36take some of the matches
21:37in pile B
21:38and put them in my hand
21:39any number
21:40it's your choice
21:41okay
21:45and the rest of them
21:46I want you to put
21:47on the other end
21:47of the seesaw
21:48from the end I'm holding
21:49and that's incredible
21:55because I can tell
21:56with the variance
21:57in pressure
21:58that there are six matches
22:01on the other end
22:02has it worked?
22:04yes
22:04six
22:05there you are
22:06well
22:11if you'd like to know
22:13how that trick is done
22:14it'd be my pleasure
22:15my pleasure
22:16to tell you
22:17but you'll have to
22:18write to me first
22:19Johnny Ball
22:19think of a number
22:20BBC Television
22:21London
22:21W1A
22:221AA
22:23but please include
22:25a stamped address envelope
22:26but time's beating us
22:28it's the end of another
22:28think of a number
22:29and the more programs we do
22:30I find the quicker
22:32they seem to go
22:33and we get less and less in
22:34so
22:36perhaps one day
22:37somebody will be able
22:38to perfect a system
22:39whereby we can squeeze
22:40a lot of things
22:42into just a fraction
22:43of the time
22:44we take
22:46that's it
22:47slightly
22:47because if he
22:48turns down
22:49swing one
22:50you'd like a go
22:51you can scrap the rest
22:53until next week
22:54bye bye
22:54applause
22:55applause
Recommended
21:55
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