0:00:05 > 0:00:08Humans are an incredible species. We've found ways
0:00:08 > 0:00:11to talk to each other on opposite sides of the world.
0:00:11 > 0:00:14We've discovered cures for terrible diseases,
0:00:14 > 0:00:18and some of us have even left this planet to explore space.
0:00:18 > 0:00:21But there's still so much left to find out.
0:00:21 > 0:00:25I'm Greg Foot. Ever since I was a kid, I've been into science.
0:00:25 > 0:00:27I've always been asking questions
0:00:27 > 0:00:29and taking things apart to understand how they work.
0:00:29 > 0:00:32I was the kid trawling through the rock pools
0:00:32 > 0:00:35and the one who tried to turn his bike into an aeroplane.
0:00:35 > 0:00:38I even went on to do a science degree.
0:00:38 > 0:00:40'And I'm still asking questions.'
0:00:40 > 0:00:42- This is going to hurt, right? - Yeah.
0:00:42 > 0:00:44'And I reckon a lot of you are too.'
0:00:44 > 0:00:47And that's what this series is all about. Getting to the bottom
0:00:47 > 0:00:50of all those questions that never get properly answered
0:00:50 > 0:00:52to reveal the secrets of everything.
0:00:58 > 0:01:02'This time on The Secrets Of Everything...'
0:01:02 > 0:01:04'..I'll be finding out why chillies burn...'
0:01:04 > 0:01:06I'm shaking!
0:01:06 > 0:01:08'..even when they're cold.'
0:01:08 > 0:01:10This is exactly what makes fires burn so well.
0:01:10 > 0:01:13'My friend Doc and I will be discovering
0:01:13 > 0:01:16'why fire doesn't always burn, even though it is hot.'
0:01:16 > 0:01:19- Is your hand heatproof or something? - No, my gloves are.
0:01:19 > 0:01:23'And we'll be exploring what happens after we die.'
0:01:23 > 0:01:27The smell is just so rank that I can no longer stand it.
0:01:30 > 0:01:32But first, I'll be finding out
0:01:32 > 0:01:36if there's any truth to one of our favourite urban legends.
0:01:38 > 0:01:41So, you're at the top of an office block and you take the lift
0:01:41 > 0:01:44because you can't be bothered with the stairs.
0:01:47 > 0:01:51But something's wrong. You're going down, but far too fast.
0:01:51 > 0:01:52SCREAMING
0:01:52 > 0:01:54What do you do? You remember hearing someone say
0:01:54 > 0:01:56that if you jump at the last minute,
0:01:56 > 0:01:59you can survive your perilous drop.
0:01:59 > 0:02:01But is it true?
0:02:08 > 0:02:10'It's time to put the legend to the test
0:02:10 > 0:02:14'with the help of a crane, a portaloo...'
0:02:14 > 0:02:16This is our willing lift drop volunteer.
0:02:16 > 0:02:19'..and our body double.
0:02:19 > 0:02:22'We're dropping him from 30 metres up...'
0:02:22 > 0:02:24All set?
0:02:24 > 0:02:27'..to see what would happen if you did nothing at all.'
0:02:27 > 0:02:29Three, two, one.
0:02:32 > 0:02:34Ooh!
0:02:34 > 0:02:36Oh, that looked painful!
0:02:37 > 0:02:40- Oh, dear. That's not good. - That's not good.
0:02:40 > 0:02:44God, if that had been me in there, I would have lost both feet.
0:02:44 > 0:02:46My ankles have completely gone.
0:02:46 > 0:02:48That is one mangled foot.
0:02:52 > 0:02:56Looks like if you stand in a falling lift, the force of the impact
0:02:56 > 0:03:00goes straight through your feet and up through your body.
0:03:00 > 0:03:02We're going to need another dummy.
0:03:02 > 0:03:06So the legend says if you jump at the last minute, you'll be fine.
0:03:06 > 0:03:08'Time to put it to the test.
0:03:08 > 0:03:10'We've rigged up a spring-loaded platform
0:03:10 > 0:03:12'to make our synthetic stuntman jump
0:03:12 > 0:03:14'just before he hits the ground.'
0:03:14 > 0:03:18Three, two, one.
0:03:22 > 0:03:23- You've done it.- Ooh!
0:03:23 > 0:03:27Look at that. Let's get in.
0:03:27 > 0:03:29Look at the state of his feet.
0:03:29 > 0:03:32It's still complete and utter...
0:03:32 > 0:03:36- That's bad. - Broken man, isn't he?
0:03:36 > 0:03:40Even though our man jumped at the last minute, he was still travelling
0:03:40 > 0:03:43earthwards quicker than his jump was pushing him up.
0:03:43 > 0:03:46So if you do find yourself in a falling lift,
0:03:46 > 0:03:49you can try and jump, but it will make such a minor difference
0:03:49 > 0:03:51to the speed you're falling.
0:03:51 > 0:03:53Plus, you don't have a glass bottomed lift,
0:03:53 > 0:03:55so you won't know when to jump.
0:03:55 > 0:03:58There is no truth to that urban legend.
0:04:11 > 0:04:13BELCHES
0:04:18 > 0:04:20Now, there's one thing that's always got me.
0:04:20 > 0:04:25If chillies are cold, then why on earth do they burn?
0:04:25 > 0:04:28It's probably because I am a total wimp when it comes to eating this.
0:04:28 > 0:04:30And it seems it's not just me.
0:04:30 > 0:04:33So spicy, I felt like I was hallucinating.
0:04:33 > 0:04:37- Stuck on the toilet for about 20 minutes.- Yeah, not good.
0:04:37 > 0:04:40It made me sweat profusely.
0:04:40 > 0:04:42Then it just came out the other end really quickly.
0:04:42 > 0:04:45I had jalapeno on a pizza and it made me fart.
0:04:45 > 0:04:48It hurt going in and then it hurt coming out.
0:04:56 > 0:04:58'To answer this, I've challenged my mate Johnny
0:04:58 > 0:05:02'to a chilli-off. 'Johnny makes the hottest food I've ever eaten.
0:05:02 > 0:05:05'But today, I'm pushing him to the limit.'
0:05:05 > 0:05:08Right, dude. This is it. Look at the state of these.
0:05:08 > 0:05:12- So I'm thinking we need to make this a proper competition.- Yep.
0:05:12 > 0:05:14I'm thinking money where your mouth is.
0:05:15 > 0:05:20The strength of a chilli is measured on what's called the Scoville scale,
0:05:20 > 0:05:22ranging from zero, with no heat,
0:05:22 > 0:05:25up to a tongue-splitting one million and beyond.
0:05:25 > 0:05:28And I've lined up these seven beauties
0:05:28 > 0:05:30to see who can handle the heat.
0:05:30 > 0:05:34Right. Easy, impossible.
0:05:34 > 0:05:36- Ready for it?- I'll give it a shot. - OK.
0:05:38 > 0:05:40- That's all right.- Sweet.
0:05:40 > 0:05:43That's because that one is just a bog-standard, normal bell pepper.
0:05:43 > 0:05:48Bell peppers register on the Scoville scale at zero. Pathetic!
0:05:48 > 0:05:50Let's go on to the next one.
0:05:50 > 0:05:53Jalapeno, 2,500 on the Scoville scale.
0:05:53 > 0:05:55- OK.- Are you ready?- I'm game.
0:05:58 > 0:06:00- HE COUGHS - That's hot.
0:06:00 > 0:06:04'Jalapenos have raised the bar and the infrared camera clearly shows
0:06:04 > 0:06:07'my face burning up.
0:06:07 > 0:06:10'But how come the chilli itself stays a cool blue?
0:06:10 > 0:06:13'It's not the temperature of the chilli that matters,
0:06:13 > 0:06:17'it's all to do with a cheeky chemical called capsaicin.
0:06:17 > 0:06:21'To get at it, I've ground up the pod
0:06:21 > 0:06:22'and soaked it in vodka.'
0:06:22 > 0:06:27Now, not all chillies have the same amount of capsaicin in them.
0:06:27 > 0:06:31The hotter they are, the higher the concentration...
0:06:31 > 0:06:35'and the higher they register on the Scoville scale. Talking of which...'
0:06:37 > 0:06:38Oh, man!
0:06:38 > 0:06:42There's a kick in the background. It's fizzing under my tongue.
0:06:42 > 0:06:44I'm just getting a tongue of fire.
0:06:44 > 0:06:48It's like I've eaten a hot coal or something.
0:06:48 > 0:06:51'All sensations, touch, taste, smell,
0:06:51 > 0:06:54'start their journey to the brain from nerve endings.
0:06:54 > 0:06:56'In this case, on my tongue.'
0:06:56 > 0:06:58Each of these nerve endings has a receptor,
0:06:58 > 0:07:00acts a bit like a valve, like this.
0:07:02 > 0:07:07When it's stimulated by, say temperature, the valve opens
0:07:07 > 0:07:09and a message is sent to the brain
0:07:09 > 0:07:12telling it how hot that thing is.
0:07:12 > 0:07:16Now what capsaicin does is it lubricates the valve,
0:07:16 > 0:07:18making it a lot more sensitive.
0:07:18 > 0:07:21The result is that even a small temperature
0:07:21 > 0:07:25that wouldn't normally be registered sends a strong signal to the brain.
0:07:25 > 0:07:28Your body thinks it's being physically burnt,
0:07:28 > 0:07:29even though there's no heat there.
0:07:31 > 0:07:34This one is an orange habanero.
0:07:36 > 0:07:40Oh, man! That is a killer.
0:07:41 > 0:07:42Oh, gosh!
0:07:42 > 0:07:44Every time you swallow, it's like...
0:07:44 > 0:07:47It's like someone is actually cutting your tongue.
0:07:47 > 0:07:50'Even though it feels like there's a bandito
0:07:50 > 0:07:52'with a knife in my mouth...'
0:07:52 > 0:07:56Ah! Ah! Ah! Ah!
0:07:56 > 0:07:59'..the chilli isn't burning me at all.
0:07:59 > 0:08:01'It's just those lubricated valves
0:08:01 > 0:08:04'screaming at my brain that I'm on fire.'
0:08:06 > 0:08:10And scientists reckon the body tries to cool down by sweating
0:08:10 > 0:08:12and increasing its heart rate.
0:08:14 > 0:08:17- That IS burning!- Dude, you've gone redder than the next one.
0:08:17 > 0:08:21Moruga, at a cool half a million
0:08:21 > 0:08:23on the Scoville scale.
0:08:23 > 0:08:25Go.
0:08:25 > 0:08:27Oh, God!
0:08:27 > 0:08:28Ah!
0:08:28 > 0:08:30Ah, ah!
0:08:30 > 0:08:35- That is... I can't even talk. - I need a scotch egg to go with this.
0:08:35 > 0:08:38I can't talk! I'm out, I can't go any further.
0:08:38 > 0:08:41I can't talk. I'm going to vom.
0:08:41 > 0:08:43'Johnny's on his own now,
0:08:43 > 0:08:45'but what he doesn't know is that the last one
0:08:45 > 0:08:48'is one of the hottest chillies in the world.'
0:08:50 > 0:08:51That...
0:08:53 > 0:08:56..is a Spanish Naga,
0:08:56 > 0:09:00one million on the Scoville scale.
0:09:00 > 0:09:02You going to do it?
0:09:02 > 0:09:04I'm going to give it a shot.
0:09:07 > 0:09:08I'll give it a shot.
0:09:08 > 0:09:13Three, two, one...
0:09:13 > 0:09:16- OK, I'm shaking. - Go!
0:09:16 > 0:09:18Come on, come on.
0:09:18 > 0:09:20Chew, chew.
0:09:24 > 0:09:27How is it?
0:09:27 > 0:09:29Erm...
0:09:29 > 0:09:30That's, er...
0:09:30 > 0:09:32HE LAUGHS
0:09:32 > 0:09:34That's hot!
0:09:34 > 0:09:36Put it there.
0:09:36 > 0:09:38Well...
0:09:38 > 0:09:42It was a valiant effort.
0:09:42 > 0:09:45My...my stomach will never forgive me.
0:09:45 > 0:09:49- I think you win this, my friend. - Thank you.
0:09:49 > 0:09:50I'll leave you to recover.
0:09:50 > 0:09:53'The fact is, chillies aren't hot at all.
0:09:53 > 0:09:57'It's just the capsaicin that tricks you into thinking they are.
0:09:57 > 0:10:01'So next time you're up against a serious vindaloo,
0:10:01 > 0:10:03'remember - it's all in the mind.'
0:10:27 > 0:10:31It's not a particularly pleasant thought, but the only thing
0:10:31 > 0:10:34that's certain with life is that we're all going to die
0:10:34 > 0:10:37and when that happens, that's it, I'm gone.
0:10:37 > 0:10:39Greg Foot has left the building.
0:10:39 > 0:10:43But my body will stay here and I'll just be like any other bit of meat.
0:10:43 > 0:10:47So what I want to know is how long does it take
0:10:47 > 0:10:49to decompose when you die?
0:11:00 > 0:11:04There are lots of things that I'll do in the name of science,
0:11:04 > 0:11:07but I don't want to rot just yet.
0:11:07 > 0:11:10This poor individual who died of natural causes
0:11:10 > 0:11:14just a few hours earlier makes a pretty good stunt double.
0:11:19 > 0:11:23So a pig would be really good for our tests to see how long it takes for a human to decompose?
0:11:23 > 0:11:27The size is about the same, their skin is really similar to humans,
0:11:27 > 0:11:30they've got the same kind of muscle to body fat ratio
0:11:30 > 0:11:33and their general physiology is quite similar to humans.
0:11:33 > 0:11:36It's as good a substitute for a human as we can get, really.
0:11:36 > 0:11:40Apart from the snout and the trotters, I suppose.
0:11:40 > 0:11:43To find out what happens to our bodies once we've pegged it,
0:11:43 > 0:11:48we're going to film this pig's decomposition 24/7.
0:11:48 > 0:11:52Although this is a fresh corpse, the pig is changing by the second.
0:11:52 > 0:11:54I thought it went stiff pretty quick.
0:11:54 > 0:11:57What you're talking about is rigor mortis,
0:11:57 > 0:11:59which is contraction of the muscles.
0:11:59 > 0:12:01It begins about three hours after death.
0:12:01 > 0:12:04Let's leave him and see what happens.
0:12:10 > 0:12:13To protect our pig from scavengers, we've covered him
0:12:13 > 0:12:15with a shelter and netting.
0:12:15 > 0:12:19But this doesn't stop the flies, which arrive almost immediately.
0:12:22 > 0:12:25Soon after, the pig's body is bloated with gases
0:12:25 > 0:12:28from its rotten flesh. Just a few days later,
0:12:28 > 0:12:30the corpse is riddled with maggots.
0:12:42 > 0:12:46There's not much left of it now. That is... That's pretty rank.
0:12:47 > 0:12:51The corpse has just been through a process called autolysis,
0:12:51 > 0:12:54that's where the cells are broken down by their own enzymes.
0:12:54 > 0:12:57It's like the body is digesting itself.
0:12:57 > 0:12:59It looks like it's burst or something.
0:12:59 > 0:13:03Yeah, that's pretty much what's happened. First of all,
0:13:03 > 0:13:07it bloated with the build-up of gases inside it, and then the body tissues
0:13:07 > 0:13:09have liquefied and purged out.
0:13:09 > 0:13:14'And once this happens, the dinner bell rings for these beauties.'
0:13:14 > 0:13:16There were flies coming almost immediately
0:13:16 > 0:13:18and that's what's led to the maggots, right?
0:13:18 > 0:13:22They laid their eggs almost immediately in the natural orifices,
0:13:22 > 0:13:27like the eyes and the snout. The eggs will have been hatching
0:13:27 > 0:13:31out into maggots and the maggots will be eating the body tissues.
0:13:31 > 0:13:34'They might be revolting, but maggots can be key witnesses
0:13:34 > 0:13:37'in murder cases. By working out how old the maggots are,
0:13:37 > 0:13:42'pathologists can calculate the victim's time of death.'
0:13:42 > 0:13:44What's all that stuff? It's all wriggling!
0:13:44 > 0:13:48That's liquefied body tissue that has then been agitated
0:13:48 > 0:13:52by the movement of the maggots, that's why it's kind of foamy.
0:13:52 > 0:13:54It's getting to that stage...
0:13:54 > 0:13:56It really is getting to that stage
0:13:56 > 0:13:59where the smell is so rank that I can no longer really stand it
0:13:59 > 0:14:00and I'm going to vomit.
0:14:00 > 0:14:03- You've reached your Waterloo. - I think I have.
0:14:03 > 0:14:05# I just dropped in
0:14:05 > 0:14:09# To see what condition My condition was in
0:14:09 > 0:14:11# Yeah, yeah, oh, yeah
0:14:11 > 0:14:16# What condition My condition was in. #
0:14:16 > 0:14:18Oh, here it is.
0:14:18 > 0:14:22- Yep, in all its glory. - And it doesn't smell as bad. - Not as bad, it still...
0:14:22 > 0:14:24Although you can still, you still get it
0:14:24 > 0:14:27- at the back of the throat. - Yeah.- Just a bit of rank.
0:14:27 > 0:14:31It's pretty gruesome to think that this is what would happen to us
0:14:31 > 0:14:33if we were left to the mercy of nature.
0:14:33 > 0:14:35But what if we were six foot under?
0:14:35 > 0:14:38Well, burial creates quite a few different conditions.
0:14:38 > 0:14:42For example, the temperature, that's the most important factor. It's much cooler,
0:14:42 > 0:14:46and the access by insects is reduced dramatically.
0:14:46 > 0:14:49And how long would my bones be there for?
0:14:49 > 0:14:53That depends on the soil conditions, but hundreds of years.
0:14:53 > 0:14:56So it looks like there's no definitive answer
0:14:56 > 0:14:59for how long it takes a human body to decompose,
0:14:59 > 0:15:03but it is all great gruesome stuff and if one thing's for certain,
0:15:03 > 0:15:06your bones are going to be around for a very long time.
0:15:26 > 0:15:31Here's Professor Logic. How do you do, Professor?
0:15:31 > 0:15:36Professor Logic is a busy man. So much to see, so much to learn,
0:15:36 > 0:15:38so much to measure.
0:15:43 > 0:15:46Professor Logic is going on a journey.
0:15:47 > 0:15:51What are you hoping to discover today, Professor?
0:15:51 > 0:15:56You're going to measure the world to find the shortest route around it.
0:16:00 > 0:16:03Professor Logic, is this strictly necessary?
0:16:04 > 0:16:10I mean, can't you just use a formula like 2 x Pi x r or something? No?
0:16:10 > 0:16:12Well, no, I suppose that would mean
0:16:12 > 0:16:16that you knew what the radius of the world was already.
0:16:21 > 0:16:24I can't see much measuring going on.
0:16:26 > 0:16:29Oh, I see. You're measuring angles.
0:16:33 > 0:16:35Because you know how high the mountain is
0:16:35 > 0:16:39and you've measured the angle between the horizontal and the horizon,
0:16:39 > 0:16:45you can work out the ratio of the world...using that formula.
0:16:45 > 0:16:47And now you can use 2 x Pi x r.
0:16:48 > 0:16:53But there's a problem because the earth is not a perfect sphere.
0:16:53 > 0:16:56It's 40 kilometres wider than it is tall.
0:16:56 > 0:17:01So if it bulges in the middle, the quickest way around the world
0:17:01 > 0:17:04would be top to bottom and back up the other side.
0:17:05 > 0:17:07That's mainly sea, Professor Logic.
0:17:07 > 0:17:10Wouldn't it be a rather lonely voyage?
0:17:11 > 0:17:14So what is the shortest distance around the world?
0:17:16 > 0:17:18Professor Logic, how far?
0:17:22 > 0:17:25Thank you very much.
0:17:25 > 0:17:27No, no, pleasure's all mine.
0:17:42 > 0:17:46# It's the end of the world As we know it... #
0:17:46 > 0:17:48Space is dangerous. Cold, dark
0:17:48 > 0:17:53and rammed full of asteroids ready to plough into the earth.
0:17:53 > 0:17:56If one did, could you survive?
0:18:00 > 0:18:03What would I do to survive if an asteroid hit the earth?
0:18:03 > 0:18:07- Where's it going to hit? - London.- Leave.
0:18:07 > 0:18:11I think I'd take everything from Primark that I could.
0:18:11 > 0:18:14- I'd probably become a lot more religious.- Start running?- Yeah.
0:18:14 > 0:18:17I don't think there'd be a lot I could do to survive
0:18:17 > 0:18:19but there'd be a big cloud of dust
0:18:19 > 0:18:22and it would get very cold very quickly.
0:18:26 > 0:18:30The earth and the moon are sitting ducks in the cosmic shooting gallery.
0:18:30 > 0:18:34The moon bears the bulk of the battle scars but, according to NASA,
0:18:34 > 0:18:38over one million objects still hurtle towards our planet every day.
0:18:38 > 0:18:39These objects can be anything
0:18:39 > 0:18:43from planet-sized asteroids a few hundred kilometres across,
0:18:43 > 0:18:50to tiny specks of dust, or even smaller fragments this sort of size called meteoroids.
0:18:50 > 0:18:52A golf ball is never going to destroy the planet
0:18:52 > 0:18:55but the thing about asteroids and meteoroids
0:18:55 > 0:18:58is that they travel unbelievably fast,
0:18:58 > 0:19:03which gives them massive amounts of potentially destructive energy.
0:19:03 > 0:19:06I can work out how hard or with how much energy
0:19:06 > 0:19:09a golf-ball-sized asteroid will hit the ground using this formula.
0:19:13 > 0:19:18Now, E is for energy, so energy is a half times the mass.
0:19:18 > 0:19:22Now, the mass of that size lump of rock is about 50 grams,
0:19:22 > 0:19:26which is 0.05 kilograms
0:19:26 > 0:19:30and the speed, well, the speed of an average asteroid
0:19:30 > 0:19:33is 30,000 metres per second.
0:19:33 > 0:19:3630,000.
0:19:36 > 0:19:41Now that is 67,000 miles per hour, which is just mind boggling
0:19:41 > 0:19:45when you think that the fastest bullet goes about 2,000 miles per hour,
0:19:45 > 0:19:47which is pretty rubbish in comparison.
0:19:47 > 0:19:50Now you square that, which means times it by itself,
0:19:50 > 0:19:51treble the number through
0:19:51 > 0:19:58and that comes out at 22.5 million joules of energy.
0:19:58 > 0:20:01That is a massive number.
0:20:01 > 0:20:06To get some idea if we could survive even a golf-ball-sized asteroid impact,
0:20:06 > 0:20:08I've asked a pyrotechnics expert
0:20:08 > 0:20:12to turn my maths into an instant meteor strike.
0:20:12 > 0:20:16Mike's worked out that we need five kilograms of high explosives,
0:20:16 > 0:20:19so that's what we're burying.
0:20:19 > 0:20:21So just about there.
0:20:21 > 0:20:25- I think this is deep enough. - Great. Perfect, perfect.
0:20:25 > 0:20:29- Cool. What's next?- Right. Now we have to bury this.- OK.
0:20:29 > 0:20:32- And connect it up to the igniter. - All right. How far do we have to go?
0:20:32 > 0:20:36- Around 400 metres. - Wow, 400 metres?- Yeah.
0:20:36 > 0:20:39It'd better be a big blast to see it from there.
0:20:39 > 0:20:44- All ready and set to go. - Over to you.- OK. Three, two, one.
0:20:49 > 0:20:52Wow, that is an explosion.
0:20:52 > 0:20:55That is cool. Wow. Can I...
0:20:55 > 0:20:59- Is it safe?- Go for it, yeah. - Can I go down?- Yeah.
0:20:59 > 0:21:00Wow!
0:21:02 > 0:21:05That is a cracking crater.
0:21:05 > 0:21:07That's like three metres across.
0:21:07 > 0:21:11And this would be caused from just a small piece of space rock.
0:21:11 > 0:21:14If you had something even about five metres across,
0:21:14 > 0:21:17that would give the equivalent amount of energy
0:21:17 > 0:21:19to 15,000 tonnes of TNT,
0:21:19 > 0:21:20which is like the atomic bomb
0:21:20 > 0:21:23that was dropped on Hiroshima in World War II.
0:21:23 > 0:21:29So why doesn't the earth look like someone's taken a shotgun to a watermelon, like the moon does?
0:21:36 > 0:21:39It's because of something that we have that the moon doesn't,
0:21:39 > 0:21:41an atmosphere.
0:21:41 > 0:21:43Check this out, all I've got is a cylinder full of air
0:21:43 > 0:21:47with a little bit of cotton wool at the bottom, that's it.
0:21:47 > 0:21:49How cool is that?
0:21:49 > 0:21:53When the plunger goes down, the air molecules are squashed together.
0:21:53 > 0:21:56With all of them rammed into a tiny space, there are more collisions
0:21:56 > 0:22:01and the temperature shoots up enough to ignite the cotton wool.
0:22:01 > 0:22:05Just air and cotton wool, no flame, and you get fire.
0:22:06 > 0:22:11The same thing happens to asteroids as they hit the earth's atmosphere.
0:22:11 > 0:22:15They are travelling so fast that the air in front of them is compressed
0:22:15 > 0:22:18and heats up to over 1,600 degrees Celsius,
0:22:18 > 0:22:23hotter than molten lava, and the asteroid simply burns up.
0:22:23 > 0:22:27In fact, the atmosphere is so good at protecting us,
0:22:27 > 0:22:31only asteroids larger than 35 metres across
0:22:31 > 0:22:34stand any chance of getting to the ground at all,
0:22:34 > 0:22:37which is why there are plenty of shooting stars in the sky
0:22:37 > 0:22:40but hardly any asteroid craters on earth.
0:22:41 > 0:22:46So for asteroid Armageddon to play out you need a very big rock indeed.
0:22:46 > 0:22:48But an asteroid is not likely to kill you
0:22:48 > 0:22:52because NASA know where all the largest near-earth asteroids are
0:22:52 > 0:22:56and there isn't one on target to hit the earth in your lifetime.
0:22:56 > 0:22:58Or your children's lifetime.
0:22:58 > 0:23:00Or your children's children's lifetime.
0:23:00 > 0:23:03Or your children's children's children's...
0:23:21 > 0:23:24AIR RAID SIREN
0:23:35 > 0:23:40It's one of mankind's oldest discoveries - how to make fire.
0:23:40 > 0:23:44And even today, it's got a sort of ethereal quality to it,
0:23:44 > 0:23:46an allure.
0:23:46 > 0:23:49But what is a flame? And why does it burn?
0:23:49 > 0:23:55# We are fires in the night. #
0:23:55 > 0:23:57What I need to help me is a fire-starter.
0:23:57 > 0:24:03A man who is a chemist, practical engineer, meteorologist
0:24:03 > 0:24:05and...Polish musician?!
0:24:09 > 0:24:11He is Dr Zbigniew Szydlo.
0:24:11 > 0:24:14I just call him Doc.
0:24:14 > 0:24:17- Today.- Yep.- I want to explore fire and flames.- Right.
0:24:17 > 0:24:21What do you want to show with these flames - smoke, heat, rapid combustion...?
0:24:21 > 0:24:25- I want some big flames. - Some big flames?- Some momma flames.
0:24:25 > 0:24:29To get a really good fire going, you need three things.
0:24:29 > 0:24:32You need a fuel to burn and that's what the woodchips are,
0:24:32 > 0:24:36you need heat to get the whole thing going and you need oxygen,
0:24:36 > 0:24:39which is what we're blowing in here, so we've got a nice supply of it.
0:24:39 > 0:24:43And the more oxygen there is, the quicker the reaction happens.
0:24:43 > 0:24:46- Is your hand heat-proof or something?- No, my gloves are.
0:24:46 > 0:24:50You need training and experience to pull this off, and Doc's got plenty.
0:24:51 > 0:24:53But don't try this at home.
0:24:53 > 0:24:58Liquid oxygen is a thousand times as concentrated as gaseous oxygen.
0:24:58 > 0:25:01This is exactly what makes fires burn so well. Allow me.
0:25:01 > 0:25:08So that's that lethal combination of fuel, heat and oxygen.
0:25:08 > 0:25:11What's happening between oxygen and wood
0:25:11 > 0:25:13is a plain and simple chemical reaction,
0:25:13 > 0:25:18which releases heat and light energy at the same time.
0:25:20 > 0:25:26It's the heat of the reaction that causes the gas to be so hot that it glows.
0:25:26 > 0:25:31But if fire is so hot, then how can I do this?
0:25:32 > 0:25:35We all know that fire can kill, so how come it's possible
0:25:35 > 0:25:39to touch flames without getting burnt? To find out,
0:25:39 > 0:25:42I'm going to set my soles on fire.
0:25:42 > 0:25:45This is now off my scale,
0:25:45 > 0:25:50which means parts of this fire are over 700 degrees. Yeah, that's kind of hot.
0:25:50 > 0:25:53Walking barefoot across hot coals is a risky business,
0:25:53 > 0:25:54but I'm hoping
0:25:54 > 0:25:58that knowing the science of how flames burn might work in my favour.
0:26:00 > 0:26:04If you take a balloon, pop it over a flame...
0:26:04 > 0:26:08Yeah, it bursts.
0:26:08 > 0:26:12But if you take one full of water and you hold that over the flame...
0:26:15 > 0:26:17..this time, it doesn't burst.
0:26:17 > 0:26:19The water has absorbed the heat
0:26:19 > 0:26:24and protected the balloon from bursting, up to a point.
0:26:24 > 0:26:29It's a really simple bit of science, but I've got to use that
0:26:29 > 0:26:32if I want to get across the coals without burning myself.
0:26:34 > 0:26:37My body is made up of about 73% water
0:26:37 > 0:26:40and, like we saw with the balloon,
0:26:40 > 0:26:42as I walk across this,
0:26:42 > 0:26:46the water should absorb the heat rather than my skin.
0:26:47 > 0:26:51Theoretically, each foot should be able to touch the coals for about a second
0:26:51 > 0:26:53before the damage kicks in.
0:26:55 > 0:26:59So despite being protected by my water content,
0:26:59 > 0:27:04if I don't get across quick enough, I could get badly burnt.
0:27:09 > 0:27:12Oh, that's warm!
0:27:12 > 0:27:13Yes!
0:27:15 > 0:27:17Yeah!
0:27:19 > 0:27:20That was amazing.
0:27:20 > 0:27:24It just goes to show, it is possible to play with fire
0:27:24 > 0:27:28and not get burnt if you understand the science.
0:27:39 > 0:27:44There are still loads of secrets out there. Next time...
0:27:44 > 0:27:45can sound kill?
0:27:45 > 0:27:50I want to see the effect of sound on these massive pig lungs.
0:27:50 > 0:27:53Will this girl kill me?
0:27:54 > 0:27:56She's hard as nails.
0:27:56 > 0:28:01And will drinking your own body fluids kill you?
0:28:01 > 0:28:03Bottoms up.
0:28:10 > 0:28:13Subtitles by Red Bee Media Ltd