0:00:05 > 0:00:08Humans are an incredible species,
0:00:08 > 0:00:11we've found ways to talk to each other on opposite sides
0:00:11 > 0:00:14of the world, we'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 > 0:00:29I've always been asking questions and taking things apart to understand how they work.
0:00:29 > 0:00:31I was the kid trawling through rock pools
0:00:31 > 0:00:35and the one that 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 > 0:00:40And I'm still asking questions.
0:00:40 > 0:00:42- This is going to hurt, right?- Yeah.
0:00:42 > 0:00:44And I reckon a lot of you are too.
0:00:44 > 0:00:46And that's what this series is all about.
0:00:46 > 0:00:49Getting to the bottom of all those questions
0:00:49 > 0:00:52that never get properly answered, to reveal the secrets of everything.
0:00:59 > 0:01:02This time on The Secrets of Everything.
0:01:02 > 0:01:04GUN BLASTS
0:01:04 > 0:01:07Can body armour really save your life?
0:01:07 > 0:01:09Did it stop the bullet?
0:01:09 > 0:01:12Why boomerangs come back.
0:01:12 > 0:01:13Usually.
0:01:13 > 0:01:17It may not look like it, but there's a lot of physics going on in this bent bit of wood.
0:01:17 > 0:01:22'And everything you need to know about being buried alive.'
0:01:22 > 0:01:24I feel weak.
0:01:24 > 0:01:28But first, the secrets of us.
0:01:30 > 0:01:36When I was born, the world record for the 100m stood at 9.93 seconds.
0:01:36 > 0:01:40Now, 28 years later, it's 9.58 seconds.
0:01:40 > 0:01:45So are humans destined to get faster and faster, or is there a limit,
0:01:45 > 0:01:49and if the fastest man on the planet can run at 27mph,
0:01:49 > 0:01:50why can't I?
0:01:50 > 0:01:53We've only got two legs, you put one in front of the other,
0:01:53 > 0:01:57you can't really go faster or you're probably going to break yourself.
0:01:57 > 0:01:59We're just going to get taller and slimmer.
0:01:59 > 0:02:01Yeah, we're constantly evolving.
0:02:01 > 0:02:04I reckon we'll definitely get faster.
0:02:04 > 0:02:07We will. In a couple of years' time, we'll be running faster than cars.
0:02:15 > 0:02:19Right, to find out why I'm not a record-breaking sprinter,
0:02:19 > 0:02:23I first need to see how far off the mark I am.
0:02:23 > 0:02:25- Set.- 'Not great.'
0:02:25 > 0:02:29At least one second slower than the slowest man here.
0:02:30 > 0:02:33Wow, they were quick!
0:02:33 > 0:02:36Granted, those guys train three days a week.
0:02:38 > 0:02:41That's not the only reason they beat me.
0:02:41 > 0:02:45My speed is limited by the amount of force I exert through my legs
0:02:45 > 0:02:46when I move.
0:02:46 > 0:02:49Each step you take, you're pushing down on the ground.
0:02:49 > 0:02:52And it may not feel like it, but the ground is pushing back up
0:02:52 > 0:02:54with the same amount of force.
0:02:54 > 0:02:57And that's what propels you along.
0:02:57 > 0:03:01The greater the force you push through your leg muscles, the faster you go.
0:03:02 > 0:03:04By running over a pressure pad,
0:03:04 > 0:03:08I'll measure how much force each one of my sprinting steps makes.
0:03:12 > 0:03:17The higher the score, the faster I should be able to run.
0:03:17 > 0:03:20Force is measured in newtons.
0:03:20 > 0:03:24When I'm just standing around being geeky, I normally exert a force
0:03:24 > 0:03:26of around 800 newtons.
0:03:26 > 0:03:28But what happens when I run?
0:03:28 > 0:03:32OK, so this says when I was running, I was pushing down on the ground
0:03:32 > 0:03:36with a force of 2,057 newtons,
0:03:36 > 0:03:39which is pretty much three times bigger
0:03:39 > 0:03:41than when I'm just standing still.
0:03:41 > 0:03:45But the reality is, to get anywhere near an Olympic medal,
0:03:45 > 0:03:50you'd need to exert a force of four times your resting body weight.
0:03:50 > 0:03:53And if you don't make the grade, blame your parents,
0:03:53 > 0:03:56because a lot of it is in the genes.
0:03:56 > 0:04:00The force that we can generate in our legs is limited by our muscles,
0:04:00 > 0:04:04and they're made up of two types of muscle fibres,
0:04:04 > 0:04:06The first is type one.
0:04:07 > 0:04:11This type of muscle is also called slow twitch
0:04:11 > 0:04:14and it's great for endurance sports like marathons.
0:04:14 > 0:04:18But there's another type of muscle called fast twitch,
0:04:18 > 0:04:20or type two muscle fibres.
0:04:20 > 0:04:23And they're used for short, explosive bouts of exercise.
0:04:27 > 0:04:31We are each born with a mix of these two types of fibres,
0:04:31 > 0:04:34and whilst we can tone up what we have,
0:04:34 > 0:04:38we can't really do anything about what nature's dished up to us.
0:04:38 > 0:04:41Fast sprinters have been shown to have a genetic make-up
0:04:41 > 0:04:46of 70% type two fibres, so to find out why I'm not winning any races,
0:04:46 > 0:04:50I need to see what's going on inside these pins.
0:04:50 > 0:04:52I've had my muscle analysed. Oh!
0:04:52 > 0:04:54I felt that!
0:04:54 > 0:04:58And its 53% type one, 47% type two.
0:04:58 > 0:05:00Not a winning combination.
0:05:03 > 0:05:06But even if humans were able to do the impossible
0:05:06 > 0:05:09and have 100% type two muscle fibres,
0:05:09 > 0:05:13there would still be a limit to how fast we could run.
0:05:13 > 0:05:16And that's because, with only two legs,
0:05:16 > 0:05:18we are just not built to run like the wind.
0:05:20 > 0:05:22Unlike this little design beauty.
0:05:26 > 0:05:31Four long legs, a huge heart and a massive 8m stride
0:05:31 > 0:05:34means a cheetah can run at over 60mph.
0:05:36 > 0:05:39Now, there's no way I'm going to be able to get a bigger heart
0:05:39 > 0:05:42and I'm going to struggle to make myself lighter or more streamlined,
0:05:42 > 0:05:46but there is something I can do about the longer legs.
0:05:50 > 0:05:54These are pro jump stilts, similar to the carbon fibre blades
0:05:54 > 0:05:59that the record breaker sprinter Oscar Pistorius runs on.
0:05:59 > 0:06:03By lengthening my stride, they should make me run faster.
0:06:09 > 0:06:12The problem people have with long legs, though,
0:06:12 > 0:06:17is they tend to move them slowly which cancels out that advantage.
0:06:17 > 0:06:19But Usain Bolt has rewritten the rulebook.
0:06:19 > 0:06:25At 6ft 5in, he's got long legs that are also fast.
0:06:25 > 0:06:28But could I have him with a pair of these on?
0:06:28 > 0:06:32Could weak genes and the wrong muscles really be swept aside
0:06:32 > 0:06:36by a pair of pogo sticks?
0:06:36 > 0:06:38Move over, Usain!
0:06:41 > 0:06:43SIREN BLARES
0:06:45 > 0:06:47ENGINE POWERS UP
0:06:48 > 0:06:50SCREECHING
0:06:50 > 0:06:53TRIUMPHANT MUSIC PLAYS
0:06:53 > 0:06:55BURGER BURPS AND BREAKS WIND
0:07:12 > 0:07:15I don't normally look at what's happening in the sink,
0:07:15 > 0:07:17but it makes you ponder the urban legend -
0:07:17 > 0:07:20does water really swirl the opposite direction
0:07:20 > 0:07:22down the plug hole, down under?
0:07:30 > 0:07:33To get to the bottom of this watery little number,
0:07:33 > 0:07:36you first need to know a bit about how the world goes round.
0:07:36 > 0:07:40This is a revolutionary bit of technology from the '80s.
0:07:40 > 0:07:42It's called a lazy Susan.
0:07:42 > 0:07:44Imagine that it's the Earth and we're looking down on it.
0:07:44 > 0:07:49So that's the North Pole and this is going to be the equator.
0:07:49 > 0:07:53I'm going to draw the path that a current of air would take,
0:07:53 > 0:07:55moving from the North Pole to the equator.
0:07:56 > 0:07:58Straight line, nothing special about that,
0:07:58 > 0:08:02but set the Earth rotating counterclockwise
0:08:02 > 0:08:04and draw the same current of air.
0:08:04 > 0:08:08This time you get a curve, because now the earth is spinning,
0:08:08 > 0:08:11the current of air veers to the right.
0:08:11 > 0:08:13But if you're in the southern hemisphere,
0:08:13 > 0:08:17it feels to you as if the Earth is spinning in the other direction,
0:08:17 > 0:08:20and that means that the current of air veers the opposite way.
0:08:20 > 0:08:23This is called the Coriolis effect.
0:08:23 > 0:08:28It causes hurricanes to spin anticlockwise above the equator
0:08:28 > 0:08:30and clockwise below it.
0:08:31 > 0:08:34So if I want to find out if this has any impact on our urban legend,
0:08:34 > 0:08:37I need an assistant in Australia.
0:08:37 > 0:08:40- Hi, Lindsay, it's Greg. - Hi, Greg!- Hiya!
0:08:40 > 0:08:43I'd like to do an experiment. I'd like to rest an old urban legend.
0:08:43 > 0:08:46What we need is a sink and we need to fill the sink up.
0:08:46 > 0:08:48So I'm going to carry you over to my sink.
0:08:48 > 0:08:50You want me to fill it up?
0:08:50 > 0:08:51Yes, please!
0:08:51 > 0:08:52OK.
0:08:52 > 0:08:56So Lindsay and I can clearly see which way the water drains away,
0:08:56 > 0:08:59we're going to put some herbs into the mix.
0:08:59 > 0:09:03- Have you got some herbs?- Well, actually, my housemate just happens to exfoliate with oregano,
0:09:03 > 0:09:05so there is some right here.
0:09:05 > 0:09:07Perfect!
0:09:07 > 0:09:10OK, so, three, two, one.
0:09:14 > 0:09:17Mine is going...
0:09:17 > 0:09:18clockwise.
0:09:18 > 0:09:19Oh!
0:09:19 > 0:09:22- Oh, oh!- Anticlockwise.
0:09:22 > 0:09:24So they are different.
0:09:26 > 0:09:29All right, let's not just leave it there with one attempt!
0:09:29 > 0:09:33Three, two, one, go!
0:09:38 > 0:09:40Mine is going...
0:09:40 > 0:09:42anticlockwise!
0:09:42 > 0:09:45No... Yes! Anticlockwise this time.
0:09:45 > 0:09:46What's yours?
0:09:46 > 0:09:48Really? Mine's going...
0:09:48 > 0:09:50Anticlockwise as well!
0:09:50 > 0:09:51Anticlockwise.
0:09:51 > 0:09:53So we're now both anticlockwise.
0:09:55 > 0:09:58Looks like the urban myth is going down the plughole.
0:09:58 > 0:10:00But we need to make sure.
0:10:00 > 0:10:02Try it once more?
0:10:02 > 0:10:04Yes, please, in the name of science.
0:10:04 > 0:10:08- OK. All right. - Three, two, one.
0:10:14 > 0:10:17Mine's going and it's going anti-clockwise.
0:10:20 > 0:10:24Mine's going anti-clockwise again.
0:10:24 > 0:10:28Is it? So both exactly the same.
0:10:28 > 0:10:32- So it doesn't really look like the urban legend stands up, does it?- Nope.
0:10:35 > 0:10:40So each time you drain you never know which way it will go.
0:10:40 > 0:10:43When you fill up your sink,
0:10:43 > 0:10:47you're causing all that water to juggle round all over the place
0:10:47 > 0:10:50and even if you leave it to settle, it's still moving ever so slightly.
0:10:50 > 0:10:55That spinning is then exaggerated as the water gets squeezed down into the narrow plughole.
0:10:55 > 0:11:00The truth is it's not the spin of the earth that affects the way water drains away at all.
0:11:00 > 0:11:04It's all down to the shape of your sink and the power of your tap,
0:11:04 > 0:11:07so the urban legend is false.
0:11:25 > 0:11:30In Kill Bill, Uma Thurman was put in a box by her evil nemesis
0:11:30 > 0:11:35and buried six feet under. Now, Uma escaped, but that's a film.
0:11:35 > 0:11:39If you were buried alive, would that really be the end?
0:11:39 > 0:11:43I would try and dig myself out, but getting out the coffin's the hard bit.
0:11:43 > 0:11:46I'd just kind of surrender to the experience, I think.
0:11:46 > 0:11:49Bang like hell and try to kick the coffin open.
0:11:49 > 0:11:51Scratch through with your nails.
0:11:51 > 0:11:53Sleep a while and wait for them to find you.
0:12:00 > 0:12:05To answer this gruesome question I'm going to get myself buried.
0:12:05 > 0:12:09This seems to be a perfect place. Looks like they've got a track record.
0:12:09 > 0:12:12You might think that it's impossible to escape being buried alive
0:12:12 > 0:12:15because you'd suffocate pretty quickly.
0:12:15 > 0:12:19So, first up, I want to work out how much time I've got to escape
0:12:19 > 0:12:23before the lack of oxygen finishes me off.
0:12:23 > 0:12:26And because I haven't got a total death wish,
0:12:26 > 0:12:31I've got an ambulance and a doctor standing by to make it all end happily.
0:12:31 > 0:12:33I'm going to seal you in now.
0:12:33 > 0:12:37- Right. So this is Perspex so you can see me.- I can see you the whole time.
0:12:37 > 0:12:41The clock starts ticking the moment my captor closes the coffin lid.
0:12:41 > 0:12:44- So I'm going to seal you in.- Great.
0:12:48 > 0:12:50From now on, all I've got to breathe
0:12:50 > 0:12:53is the air sealed into the box with me.
0:12:53 > 0:12:57Ned's going to measure the oxygen in blood
0:12:57 > 0:13:00and the makeup of the air trapped in the coffin.
0:13:00 > 0:13:04As I breathe in oxygen I breathe out carbon dioxide or CO2
0:13:04 > 0:13:10and after just three minutes it's the CO2 which starts causing problems.
0:13:10 > 0:13:11That's the alarm.
0:13:11 > 0:13:17That's our safety feature to know we're going far out of the normal.
0:13:17 > 0:13:21- Oh, great(!) So, even though that alarms gone off, we're still going? - We're still going.
0:13:21 > 0:13:24The CO2 that's building up in my blood
0:13:24 > 0:13:27makes it a lot harder for my blood cells to take up any oxygen
0:13:27 > 0:13:30even if it's there in the air that I'm breathing.
0:13:30 > 0:13:34There's a battle going on inside me.
0:13:34 > 0:13:37The more carbon dioxide there is in my blood,
0:13:37 > 0:13:40the less space there is for the oxygen needed to keep me alive.
0:13:40 > 0:13:44And because, like me, the carbon dioxide can't escape
0:13:44 > 0:13:47it's getting more concentrated in the air
0:13:47 > 0:13:51and in my blood and struggling to get out just makes things worse.
0:13:51 > 0:13:54Got to act like I was trying to break out.
0:13:54 > 0:13:57Using your muscles, using more oxygen, producing more carbon dioxide.
0:14:03 > 0:14:07I just feel really, like, groggy.
0:14:07 > 0:14:09Ned's decided I've had enough.
0:14:09 > 0:14:12- So we're going to get you out of there.- Fresh air, come on.
0:14:14 > 0:14:17Oh!
0:14:20 > 0:14:24So the question is how long would I survive
0:14:24 > 0:14:26if I was really buried alive?
0:14:26 > 0:14:27Ah, man.
0:14:27 > 0:14:29When you're fighting to get out the box,
0:14:29 > 0:14:33we saw the oxygen levels dropping by about 0.5% in a minute,
0:14:33 > 0:14:38- so you've probably got about, if you're really going for it, 16 minutes maximum.- Ah, man.
0:14:38 > 0:14:44So when it comes to being buried alive, time is definitely not on your side.
0:14:44 > 0:14:47Next up, I want to find out whether it's possible
0:14:47 > 0:14:50to break out of a coffin in less than 16 minutes.
0:14:50 > 0:14:56But this time Health And Safety have advised that a little oxygen wouldn't go amiss.
0:14:57 > 0:15:03Ready to start the stopwatch? Three, two, one, go.
0:15:06 > 0:15:07# Shut up and let me go
0:15:07 > 0:15:10# This hurts, I tell you so
0:15:10 > 0:15:11# For the last time you will kiss my lips
0:15:11 > 0:15:14# Now, shut up and let me go. #
0:15:14 > 0:15:18Not much space in these things.
0:15:18 > 0:15:20Argh!
0:15:23 > 0:15:25# Shut up and let me go. #
0:15:27 > 0:15:29Five minutes 20.
0:15:29 > 0:15:32It's taken me just over five minutes to break out the coffin,
0:15:32 > 0:15:35but if I had truly been six feet under
0:15:35 > 0:15:38I would still have had an awful lot of digging to do.
0:15:38 > 0:15:39- You ready?- Yep.
0:15:39 > 0:15:41So we've rigged up this escape tunnel
0:15:41 > 0:15:45to see whether I could get through in the ten minutes I've got left.
0:15:45 > 0:15:47Top up on the oxygen.
0:15:47 > 0:15:49Go, good luck.
0:15:54 > 0:15:57# Making my escape, making my escape
0:15:57 > 0:16:00# Tell myself that everything's in shape, everything's in shape... #
0:16:02 > 0:16:06Well, sadly that's 16 minutes over.
0:16:06 > 0:16:09Ah, what, so I'm dead?
0:16:11 > 0:16:14I feel like I've been vacuum packed.
0:16:14 > 0:16:19Someone in the movies escaping from being buried alive?
0:16:19 > 0:16:21It's just not possible.
0:16:21 > 0:16:25# We can be happy underground... #
0:16:25 > 0:16:28- Pub?- Let's.- Pub.
0:16:28 > 0:16:32I don't know if they'll serve me like this, to be honest.
0:16:32 > 0:16:35"Oh, where have you been?" "Oh, I've been buried alive."
0:16:50 > 0:16:54Here's Professor Logic. How do you do, professor?
0:16:54 > 0:17:00Professor Logic is a busy man. So much to see, so much to learn,
0:17:00 > 0:17:02so much to measure.
0:17:08 > 0:17:13It's a miserable day, but Professor Logic doesn't mind bad weather.
0:17:13 > 0:17:17For him it's simply a chance to find out more about the world.
0:17:22 > 0:17:24Today, Professor Logic is puzzled.
0:17:24 > 0:17:27He knows that clouds contain many tonnes of water
0:17:27 > 0:17:30but he also knows they float in the sky,
0:17:30 > 0:17:32so he's off to take a closer look.
0:17:34 > 0:17:38What can you see, professor? Tiny little drops of water?
0:17:38 > 0:17:39May I?
0:17:39 > 0:17:43Gosh, professor, the drops of water are so small
0:17:43 > 0:17:46that they're being held up by the air molecules.
0:17:46 > 0:17:50No wonder they don't fall out of the sky.
0:17:50 > 0:17:52But why are they in the sky in the first place?
0:17:56 > 0:17:58That's very pretty, professor.
0:17:58 > 0:18:00What is it?
0:18:00 > 0:18:02It's water?
0:18:04 > 0:18:07I see, the sun heats up the surface of the sea
0:18:07 > 0:18:11and water evaporates into the sky and when it cools down way up there
0:18:11 > 0:18:15it condenses back into tiny droplets of water.
0:18:15 > 0:18:19But the drops are so small that they float about in clouds
0:18:19 > 0:18:23until the tiny drops form bigger ones and spoil all the fun.
0:18:27 > 0:18:32Professor Logic, I think it's time to get back to the lab now.
0:18:57 > 0:19:00Throw a stick...
0:19:00 > 0:19:01and it doesn't come back.
0:19:01 > 0:19:05But throw a bent stick that's been nicely shaped...
0:19:09 > 0:19:16Yes! Now it may not look like it, but there's an awful lot of physics going on in this bent bit of wood.
0:19:16 > 0:19:20So why do boomerangs come back?
0:19:26 > 0:19:30If there's anyone I know who can help me, it's a man who is a chemist,
0:19:30 > 0:19:34practical engineer, a meteorologist and...
0:19:37 > 0:19:39Polish musician?!
0:19:39 > 0:19:43He is Doctor Zbigniew Szydlo.
0:19:43 > 0:19:46I just call him doc.
0:19:46 > 0:19:49I need you to cut out some shapes that look like this boomerang.
0:19:49 > 0:19:52- Yep, no problem. - Then we can do a few test flights
0:19:52 > 0:19:56and work out the vital ingredients that give this boomerang flight.
0:19:56 > 0:20:00First things first, I want to show doc my boomerang-throwing skills
0:20:00 > 0:20:03That was pants.
0:20:03 > 0:20:05Yeah, I may not be able to catch it very often
0:20:05 > 0:20:08but even a muppet like me can get it to fly in a nice big circle.
0:20:08 > 0:20:13But what is it that makes a boomerang fly?
0:20:13 > 0:20:15Now this may look like a flattish bit of wood
0:20:15 > 0:20:17but, in fact, it's a cunning bit of engineering.
0:20:17 > 0:20:24If you look down one of the blades, you'll see that actually one side is thick and the other side is thin.
0:20:24 > 0:20:27What you've got is the basic aeroplane wing shape,
0:20:27 > 0:20:30and it's exactly the same on this side too.
0:20:30 > 0:20:33What you've basically got are two plane wings.
0:20:33 > 0:20:39Wings create a force called lift and it's what makes a boomerang fly.
0:20:39 > 0:20:41Right, here we go, yes.
0:20:41 > 0:20:47But it doesn't explain why they have a habit of returning to their owners.
0:20:47 > 0:20:51That's all to do with the way boomerangs spin as they fly through the air.
0:20:51 > 0:20:56Things that spin, like this gyroscope, act in a very weird way.
0:20:56 > 0:21:00If I tip this forwards, it spins round.
0:21:00 > 0:21:03That is not me doing it.
0:21:05 > 0:21:08They call that gyroscopic procession.
0:21:08 > 0:21:13So by tipping something that's spinning, you get it to turn,
0:21:13 > 0:21:17just like when you were showing off on your bike hands free.
0:21:17 > 0:21:20But what's this got to do with boomerangs?
0:21:20 > 0:21:23If I now move the wheel through the air,
0:21:23 > 0:21:25the spokes at the top are moving even faster
0:21:25 > 0:21:29because they've got the initial speed plus the speed of me moving it through the air.
0:21:29 > 0:21:31Same for the boomerang.
0:21:31 > 0:21:35Its wings move faster through the air at the top of its spin so tipping force is greatest up there.
0:21:35 > 0:21:40It forces it like that, tips it down and around it goes.
0:21:40 > 0:21:44The gyroscopic procession. Crazy-ass physics,
0:21:44 > 0:21:48but we're pretty much there explaining why boomerangs come back.
0:21:50 > 0:21:52Of course, doc already knew all of this
0:21:52 > 0:21:55so it's time to see what he's come up with.
0:21:55 > 0:22:00Right, Greg, here it is. As you asked I've shaved off there
0:22:00 > 0:22:05at the top in the middle, cut them into here, so to make it lighter in the middle, heavier on the outside,
0:22:05 > 0:22:08Let's hope it does the trick. The moment of truth.
0:22:17 > 0:22:20Come on, come on, ah!
0:22:20 > 0:22:24All right so I didn't catch it but it did come back.
0:22:24 > 0:22:28And spinning things, gyroscopes, are in loads of our technology
0:22:28 > 0:22:33from smart phones to games consoles, satellites to spaceships.
0:22:33 > 0:22:36The modern world explained by a bent stick.
0:22:56 > 0:23:00In some jobs you have to be prepared for pretty much anything,
0:23:00 > 0:23:03including the possibility of being shot at
0:23:03 > 0:23:07and bulletproof vests come as part of the kit.
0:23:07 > 0:23:11But what I want to know is just how can a vest protect human flesh
0:23:11 > 0:23:13from the impact of a speeding bullet,
0:23:13 > 0:23:17and can they ever be 100% bulletproof?
0:23:21 > 0:23:27To answer this one, I've come to meet a man who knows a thing or two about bullets.
0:23:27 > 0:23:30What would happen if you weren't wearing a bulletproof vest?
0:23:30 > 0:23:34What we've got here is a pig's leg from the butchers
0:23:34 > 0:23:36and we're going to fire a bullet into it
0:23:36 > 0:23:39and see if we can see anything interesting.
0:23:39 > 0:23:43It's not that usual to be using your Sunday lunch as target practice
0:23:43 > 0:23:47but, anatomically, pigs are a pretty close match to us
0:23:47 > 0:23:50which makes them excellent stunt doubles.
0:23:50 > 0:23:52Three, two, one.
0:23:57 > 0:23:59Wow, that was loud.
0:24:01 > 0:24:02That's a tiny, tiny hole.
0:24:02 > 0:24:06Did it go through, that's the question.
0:24:06 > 0:24:08And yes it did. Soft targets like flesh,
0:24:08 > 0:24:11bullets find it very easy to just punch their way through.
0:24:14 > 0:24:21It looks like the 900mph bullet has ripped a clean line through the pig.
0:24:21 > 0:24:24But because we can't see what happened on the inside,
0:24:24 > 0:24:27we're going to fire at transparent ballistics gel,
0:24:27 > 0:24:30developed by scientists to represent human tissue.
0:24:36 > 0:24:39What we can see left is this one trail,
0:24:39 > 0:24:43this cavity that the bullet has left as it passed through.
0:24:46 > 0:24:50To stand any chance of protecting our soft flesh from a speeding bullet,
0:24:50 > 0:24:53you'd expect a bulletproof vest to be rock hard
0:24:53 > 0:24:56but that isn't always the case.
0:24:56 > 0:25:00This is light and it's really flexible as well.
0:25:00 > 0:25:05Well, the reason for that is this is made of multiple layers of Kevlar
0:25:05 > 0:25:08which is essentially made from a plastic,
0:25:08 > 0:25:10and it's a soft type body armour.
0:25:12 > 0:25:13Lets see what it does.
0:25:13 > 0:25:16Three, two, one...
0:25:21 > 0:25:24Right, well, look, that's where it went through.
0:25:24 > 0:25:26You can see it where it struck.
0:25:28 > 0:25:29Did it stop the bullet?
0:25:31 > 0:25:32Yes, it did.
0:25:32 > 0:25:36What a material. What a material. A plastic that can stop bullets.
0:25:36 > 0:25:39Now, if you think of when you kick a football to a football net,
0:25:39 > 0:25:42the football net catches the football,
0:25:42 > 0:25:47and that's what the Kevlar is doing, except that in this case
0:25:47 > 0:25:51the net is very, very strong and that's what catches the bullet.
0:25:53 > 0:25:57Although Kevlar is very effective against handgun fire,
0:25:57 > 0:26:00it's pretty much useless against rifle rounds.
0:26:00 > 0:26:02Yeah, two holes, gone through.
0:26:02 > 0:26:05Time to bring out the daddy of all bulletproof vests.
0:26:05 > 0:26:08So what we've got here is a face plate
0:26:08 > 0:26:11and this face plate would have a ceramic tile inside.
0:26:11 > 0:26:16- Ceramic? So what, like your plates at home?- So, not dissimilar.
0:26:16 > 0:26:19It seems we've upgraded from a football net to a dinner plate.
0:26:19 > 0:26:25It's going to have to be some piece of crockery to stop a 2,000mph rifle bullet.
0:26:31 > 0:26:34It's gone about half the way through the ceramic
0:26:34 > 0:26:38but it's not come through the back. So that sniper rifle bullet
0:26:38 > 0:26:41went straight through Kevlar but not through this.
0:26:41 > 0:26:45The fact is there are thousands of different types of ceramic
0:26:45 > 0:26:49and the stuff inside the vest is nearly as hard as diamond.
0:26:52 > 0:26:54As the bullet comes into contact with the ceramic,
0:26:54 > 0:26:59the energy of the bullet is being spread over that much larger area.
0:26:59 > 0:27:02- So the Kevlar is like a football net catching the ball?- Quite.
0:27:02 > 0:27:06And this is like just putting up a riot shield and it just bouncing back off.
0:27:06 > 0:27:09That's right, an disruptor so it can't penetrate through.
0:27:09 > 0:27:11Good stuff, wow, pretty impressed with that.
0:27:11 > 0:27:14Sniper rifle - and you're still going to be alive.
0:27:15 > 0:27:19So they may look like a plastic net and a very strong dinner plate
0:27:19 > 0:27:24but, together, they're the technology that really do make bulletproof vests...
0:27:26 > 0:27:28..well, bulletproof.
0:27:28 > 0:27:32There are still plenty more secrets out there.
0:27:32 > 0:27:36Next time, discover how good swearing is at helping with pain...
0:27:36 > 0:27:41- BLEEP! BLEEP! BLEEP!- It's going.
0:27:41 > 0:27:44..spontaneous combustion - the facts...
0:27:44 > 0:27:46It feels nice and warm here,
0:27:46 > 0:27:50but the rest of the room is still completely untouched.
0:27:50 > 0:27:53Do you reckon you'll be able to hit me from up there?
0:27:53 > 0:27:57..and the truth behind the legend - could a falling penny ever prove fatal?
0:27:57 > 0:27:59Let's do this.
0:27:59 > 0:28:01The things they make me do for science.
0:28:14 > 0:28:16Subtitles by Red Bee Media Ltd