Fantastic Elastic

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BBC Sounds, music, radio, podcasts.

Hello, I'm Brian Cox.

Hello, and I am Robin Ince.

And this is the Infinite Monkey Cage.

Now, perhaps the question we're most often asked is: what is the Infinite Monkey Cage made of?

Now, because of the scale of the construction project, we only ever made one, of course.

And it did take ages.

And if I'm honest, we haven't really finished it.

Don't tell the BBC, because initially we said it would cost about fifty quid, not realising quite how many materials we would need for an infinite monkey cage.

It is, I don't even really think we've started, to be honest.

Still, though, I think we we could change builders, we could it's taken a while.

Yeah, we're using a company called Hilbert's Builders.

One, you can never get hold of them, you're just kept on call waiting the whole time.

And by the way, Bron, I'd just like to say that the one person in the room who suggested that this introduction was too in, I think, was correct.

Anyway,

let's continue reading it anyway.

I want to say it's a number theory joke.

How many of those are there?

So anyway, that is why we're here.

We're here for number theory jokes.

We're also here to explain why we created an infinite monkey cage, or at least started creating an infinite monkey cage, out of elastic and rubber bands.

And it's a beautiful cage.

Not all of the monkeys like it.

They don't like it if you flick them too much.

Some of them like it a lot if you flick them too much, so I don't quite know what's wrong with those monkeys.

Have I left the script too far for you now?

Have I now

I've jettisoned too early on?

Okay, Brian, you just say that the okay, I'll say it.

Anyway, it gets bigger and bigger and bigger forever, and then you say, just say the comedy line.

Which was a bit of a stretch.

There we go.

Brian, we've got that out of the way.

So, today,

yes, we're allowed to be meta every now and again.

We get accused of dumbing down here at the BBC.

there it is that's dumbing up to an extremely high level you've got to know you've got to have a degree in number theory to get the joke i'll tell you what you were right to drop that joke you were going to do what was the punchline to that one

oh about a pole in the complex plane yep good grabby didn't do that one so

it was about contour integration where you get one over one minus x right so so if x is one someone said yes which would actually mean stop you've got to stop now

you've got to integrate around that because it's undefined

Anyway, so this week, as you can see from that introduction, we're talking about elasticity.

What is the stretchiest known material?

Why are some things able to stretch and some not?

What happens at the molecular level when a material stretches or shrinks?

To help us expand our knowledge of elasticity, we are joined by two material scientists, a comedian, and the world's greatest trampolinist.

And it seems ridiculous that it's taken us nearly 200 episodes to finally get a gold medal winning trampolinist on.

In fact, they probably won't make a show after this.

This is the end of it all.

And they are.

I'm Anna Podaiski.

I'm a materials scientist and writer, and my favourite application of elasticity is waistbands.

Hi, I'm Brownie Page, Olympic champion in trampoline, and my favourite application of elasticity is, of course, trampolining.

Hi, I'm Jess Fostercue.

I'm a comedian and I'm a feminist, but my favourite application of elasticity is spunks.

Hi, everybody.

I'm James Busfield.

I'm a professor of materials who specialises in rubber elasticity.

And my favourite application is anything that Wiley E.

Coyote has tried to do to catch the road runner.

Oh, this is a panel.

Now, we're going to begin with the definition.

So, James, given that you're a professor of elasticity, essentially,

that's not your title, I know, but no, it's yours.

But given that's your specialist area, is there a definition?

What does elasticity mean to a scientist?

So, if you turn the clock back to the time of Robert Hooke, who invented the sort of concept of elasticity,

when you take a solid and you deform it like a spring, and you let go of it, it goes back to its original shape.

That is essentially the concept of elasticity.

And that's been applied then as a way of characterizing materials.

And if you go on a bit later on in history, you end up with Thomas Young, and he comes up with an idea that he can measure the modulus of a material.

And that modulus of the material is a way of characterizing its essential stiffness of that material.

So, get back to your earlier question as to how you think about elasticity.

Any material that you stretch and then let go and it goes back to original shape, that's an elastic solid.

And we have ways of measuring how different materials compare against each other.

So, this is when we see a number being put on, so Young's modulus.

Everyone who's done science at school will know Young's Modulus.

Before that, what are we seeing in terms of historically within the world of elasticity?

I guess the main thing I think of is the the Mesoamericans and their love of natural rubber.

Natural rubber trees, they're from Brazil originally,

and the Aztecs and the Mayan people had loads of rubber.

They loved this stuff.

They would make shoes out of it, they invented games out of it, they made bouncy balls and they they created these big

temples in which they would play these

games with rubber balls.

And what's happening?

So if we go down to the molecular level, so when something like a rubber band, for example, what's happening when you stretch a rubber band?

An easier way to describe it is actually going back to metals because they're sort of simpler materials.

So when you stretch a metal,

the atoms are very strongly bonded together and you stretch it a little bit and they move very slightly further apart.

But the forces of physics force them to come back together again, and that's elasticity.

I just wanted to quickly go back to the Mayan temples with the elastic made out of natural fibre, the balls.

Is that the origin story of squash?

So, the meso-Americans, when they played these games, the victor, the person who won the ball game, was often killed in a ceremony to demonstrate his devotion to the sport.

Wow,

I think there are still some businessmen who play squash like that.

But why did anybody ever win?

Was it a very low-scoring game?

It's like nil-nil again.

It was an honour to be the victor and therefore sacrifice yourself.

Now, Bryony, in terms of trampolining,

is there a difference?

Because we've all sort of bounced around on a trampoline at some point in our lives.

But when you go to an Olympic trampoline, this tremendously sort of presumably elastic thing, are they more or less less bouncy than the little ones?

Of course, like Olympic trampolines are extra bouncy,

as you might imagine, but that means it's more force going through the body as well.

And they're a bit more chaotic.

So if you aren't holding your body line in the trampoline and your strength, you'll just get kind of jumped off the trampoline, essentially.

So, by chaotic, you mean it'll throw you off in any direction?

Well,

whichever way your body is weak, if you lose the power through your knees or your core isn't strong enough and you kind of slip your hips, you'll go to the side and be sprung off the trampoline.

So, you've got to be really strong.

So, essentially,

if you're going to throw something like a block of wood on the trampoline directly straight, it's going to go straight back up.

But if you drop something that's wobbly, like an elastic band, it might just ping off another way because it's not got any force to it.

How is it so

palatable?

But also chaotic.

It's interesting.

Is that a payoff?

There is clearly some issues.

So, Olympic trampolines, they're very elastic, so that you get all the energy that you created and make it so you can jump yourself four and a half miles.

Not creating the energy, I just, as a physicist.

Brian refuses to be a creationist.

I will avoid any more biblical illusions at this juncture.

As the trampoline passes,

they travel through the middle.

So ultimately, a lot of the elasticity of your trampoline comes from the metal springs all around the edges.

So if you've got a rubber device, you're dissipating energy, it's a viscoelastic material.

If you've got a metal spring, you get the energy release immediately given back to you with very little energy lost.

So you're making use of the metal springs that are around the perimeter.

And the mat itself is made out of polypropylene or anyl material that doesn't stretch a great deal.

So actually what you're doing is you're transferring your kinetic energy into stretching the springs and you get all that energy back and then you stretch your legs and you get a little bit higher every time or you do whatever maneuver you're trying to do.

So, in practice, you're exploiting metal elasticity from the springs.

And the oldest trampolines, they were actually bungee rigs.

So, instead of springs round the side,

it was rubber bands or thick string rubber bands.

And then the different types of trampoline you can get instead of just webbing, which is elastics, it can be string beds as well.

And then we've got super tramps, which aren't a competitive trampoline, but they can be used as a tool to learn new skills because it's essentially like a bigger trampoline.

Did you just call it a super tramp?

A super tramp.

Isn't that the greatest tribute band where you've basically just got four musicians bouncing up and down singing breakfast in America?

I think that would be beautiful.

Jess, I know you spend obviously a lot of time in the gym.

You did an incredible show called Hench about, you know, kind of the training that you've done.

Do you ever look towards the kind of you know, the

trampoline end and think, oh, do you know what?

I just'm sick of lifting things.

I'm going to, do you know, has that ever been part of your

no,

it's the honest answer, um, but I do trampoline for fun sometimes.

Uh, I've got an eight-year-old, and

you know, there are places where you can just go for a laugh, and every now and again the lights will go, the lights will go on disco, and the music will really ramp up.

But I tell you what, the first time I went with him, I got cocky.

It's the first time I trampolined since my own childhood, and I was all out.

There were some flips, there were some tuck jumps, and I don't know, I know it's radio four, but I'm just going to be honest, I'd overestimated the state of my pelvic floor.

Lesson learned.

Learned the hard way.

How high do you get in in Olympic competition?

How high do you get?

So we're like about eight to ten meters.

So if you put trampoline underneath the diving board, we'll touch Tom Daly's feet essentially.

And if you're a man, you might go a little bit higher.

But

yeah, jumping on top of a double-decker bus.

So it's not without risk if you land wrong and go flying off.

Yeah, definitely not.

And that's like a huge part of trampolining: is that that mental game and just being able to be brave enough to do it.

But I actually prefer jumping higher than I do if I have to, if I'm losing my height in the trampoline and in the routine, that's more scary to me because I have less time to figure things out and if something goes wrong.

So the higher we jump, although if we fall off the trampoline, it's not going to be super, super good.

I know, I just wondered, thinking about, you know, we're at the moment thinking of jumping up and down, but in terms of, I was thinking about bungee ropes, and

I would never do anything like that because I find life creates enough anxiety without jumping off a cliff.

But you know, in terms of working out the, I mean, there is a very, very

kind of high-risk checking of elasticity, isn't there?

So, how, for instance, is something like that is the process of checking a bungee rope before you jump?

With all materials, you can stretch them to a certain amount and then they break, generally.

Very brittle materials don't stretch very much before they break.

Very elastic materials stretch a lot.

And with a bungee rope, I would imagine there would be an element of stretching it and making sure that it is not getting to its critical limit at which it's going to snap.

But also checking the material to see has it degraded over time, because elastic materials

there can be changes in the atomic structure as you stretch them and then they go back and stretch them and they go back and over time it can what we call fatigue

and eventually that can cause them to break.

And James, if we go down to the the molecular, it's where I'm happiest, the atomic and molecular level.

So we go back to my.

So if something breaks,

what is the molecular level description of that?

Because

it seems strange that something would break all at the same time, which is what happens when a material fails.

So bunges are unusual because they're made of cord, so there's lots of individual filaments within a bungee.

So if one breaks, the other 900 will support you.

So bunges are designed to avoid that problem.

But in practice, you're absolutely right.

What drives the fracture mechanics of a material when it gets beyond its strength limit is you get a new fracture surface created.

And for most materials, that relates to something like the surface energy that's required to create the new material.

So, you can calculate how much energy is required to break a rubber band, for example.

And but by fracture surface, so what how am I to visualize that?

What's happening?

So, on the atomic scale in a rubber band, you've got lots of lots of individual long-chain molecules.

As they get stretched, they all line up.

And so those molecules are starting to form a line.

And when you start to fracture them, one will ping, and then it puts more stress on its neighbor, and then that will ping.

So it's like a chain reaction.

It's a chain reaction, a cascading chain reaction, yes.

But if you can dissipate that energy by cleverly spreading it to lots of neighbors when one breaks, then you make the material tougher.

And that's essentially what happens with rubber bands.

So Anna's about to break a rubber band, it would appear like, and she's struggling.

She's got a cis-polyisoprene natural rubber.

Oh, it's got a tiny bit.

Why would she do that?

Anna is trying to break a rubber band, and it looks like it's going to be horrendously painful.

Do you want me to try it?

Yes, right, Brianny, cover your eyes.

This is.

Oh, no.

Oh, actually, can't do it.

She can't do it.

It's really strong.

But it's surprisingly tough.

I nominate Jess.

I wonder if it'll be a bit more difficult.

It feels like the right time to.

We're talking about things that are broken.

And, Jess, you recently were broken, weren't you?

Yes, in the mind.

No, yeah, I was.

But you had, what was it, your arm or your.

I broke my arm and wrist in one injury, yes, in a gymnastics injury,

where my body went one way and my hand stayed in one place as it was stuck there.

And so, yeah, my arm bones snapped in half.

You now have titanium in there as as well?

Titanium plate, seven pins, and for a while, for seven weeks, I had a key wire in my wrist as well to make sure that where that was reset, that was going to reset in a stable way, which it has.

But that, I'm just, I'm fascinated to think about, you know, everything,

as far as I know,

in terms of solids, it's considered that everything has some sense of elasticity.

And natural materials like bone are a really nice example of the materials' properties being honed over millennia, not through creationism, through evolution,

to do a really, really good job most of the time, unless we do something that they're not designed to do.

And so, bone we can think of as a composite material.

Sort of two primary elements of it are the mineral side of it.

And if it was just minerals, it would be incredibly brittle.

It also needs the more fibrous-type

substance, more polymer-like substance.

And those two things together give it strength and stiffness, but also an element of pliability and energy absorption, which means that most of the time, if we're throwing ourselves around, we don't break our bones.

And, James, so I was just wondering with Jess now, but now with the titanium, how's that working together with the bones in terms of exercise and movement?

So, there's a really good point here that when we're looking to support a body with a prosthetic implant or something like a plate that you've had implanted, you want to make it appear and behave just like the bone used to behave.

And so you've got this problem that metals, going back to this thing about the Young's modulus, they've got modulus of 200 plus gigapascals, which is just a random number I'm going to throw out.

But your bone is around 20 gigapascals.

So it's an order of magnitude less.

So the consequence is, if you put in a piece of metal made out of stainless steel, it's going to be 10 times stiffer than the material that it's replacing.

That's why they've put a titanium plate inside you.

That's only about 70 gigapascals, only about three times stiffer than the bone.

What happens if you put something really stiff inside your body?

It takes all the stresses.

So it's really important from a biomechanics point of view that we keep loading the bone, the bone around it.

So I must keep weightlifting.

You've got to keep weightlifting.

And swimming and other less dangerous sports.

You mentioned steel there, because steel is sort of a counterintuitive thing to me, because you mentioned

we think of it as completely undeformable and the strongest thing you can imagine.

But it's also one of the most elastic materials.

Different steels behave in different ways.

So some steels are very ductile, which means at low forces they start to plastically deform.

And that's the sort of steels that you make your car door panel out of.

If somebody runs into it, it doesn't suddenly spring back to its original shape.

Some steels, like the ones inside your watches that you wind up, are made out of spring steel.

And they have a very high elastic limit, which means they're very strong.

So you can actually absorb a lot of energy in springs that allow you to sort of store it and reuse it to power your watch or to do whatever.

Brony, I just wonder, in terms of the risks that you're taking, in terms of you know, what have you had to learn a lot about, you know, again, the amount of stress you can place on your bones, that ability when you're jumping up and down a trampoline to go, oh, hang on a minute, I think I need to stop at this point.

Do you get those kind of senses of your own possible fragility at times?

Yeah, I wish I'd known this a few years ago.

So

the loading of the bone, I've actually experienced bone bony stress, essentially a stress rapture from jumping too much without listening to my body to the point where you're jumping and it feels like you know someone's putting shards of glass into your leg and you're like, what's going on?

So if I listened to my body earlier to know that I've been overloading it, then that would have helped me not get to that point in bony stress and actually just loading it in a better way to be able to to deal with the volume of of trampolining and the the stress that we put our bodies through.

So when kind of bring bring it back to that maximum depression of the trampoline when it's fully as close to the floor as you're going to get through the trampoline,

that can be like more than 15 times our body weight.

That is a huge amount of force going through our bodies that we have to be able to withstand.

And we're not just doing that once, we're doing that, you know, hundreds of times in the training session.

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10.

James, when we're talking about materials, so you mentioned earlier, you both mentioned the historic use of materials, rubber rubber and so on, natural materials.

But if we come to the present day, your research, developing new materials,

how do you go about that?

If you have a specification for something that has a particular elasticity, particular properties,

what kind of work are you doing in the lab?

So, the rubber that's been around since the Mesoamericans, that cis polyisoprene, the natural rubber material that you find, is still widely used.

In fact, it's the most commonly used rubber on the planet.

So, if you've got a car tyre, it contains some element of that.

So, nature got it right, essentially.

Essentially, yes, and it's quite miraculous in the way it behaves.

So, it's very tough, as we demonstrated with the elastic band earlier, and it's got fantastic properties.

One of the strangest things is if you take a rubber band, it's amorphous.

The polymer chains are amorphous.

You stretch it, you line them up.

You've changed its entropy.

It's second-order thermodynamics.

I'm sorry, it's a bit geeky for a radio 4 audience.

No, this is brilliant.

Now I understand.

And the universe is moving forwards in time, always increasing entropy.

So it wants to go back to a chaotic state.

So what's driving a rubber is its desire to go back to its completely random conformation.

So that's what we're familiar with when we have an elastic band.

We stretch it, second law of thermodynamics, Q equals T ds, and you let go and it goes back to its original state.

I should have thought of that.

Just to say, so what you're doing is you're ordering the structure as you stretch the thing.

Exactly.

So, you're decreasing the entropy.

You are, which is not the way the universe wants to work.

We want to have an ADHD.

The universe has got ADHD.

Yeah.

And then.

So, it's an entropy spring, a rubber band entropy spring.

Looking at what we're trying to do, the future is about trying to make these entropy springs do better things.

So, if you take the car type as an example, we're all familiar with car tyres.

We go and buy a new car tyre.

We've got this label on it from the EU, which we still keep, and that EU label tells us about the rolling resistance of the tyre.

It tells you how much fuel it's going to consume.

I suspect most of the audience don't realize this, but every time you drive your car, about a quarter of all the fuel you put in the tank or the juice you put in your battery is consumed on heating up your tyres.

It's actually generating that rolling resistance.

That, from an environmental point of view, is a disaster.

We want to reduce the energy that's dissipated.

So I spend a lot of my life trying to think about how to reduce the rolling resistance of car tyres.

The other thing that's on the label that's sitting there is about how safe is it to grip the tyre onto the road.

So if you slam on the brakes, the child runs out in front of you, you slam on the brakes, you're going to stop in time.

So you've got these two measures that you're using to judge how effective the tyre is.

And they are diametrically opposed to each other.

You need for good friction, you need lots of viscoelastic energy dissipation.

For low rolling resistance, you want no energy dissipation.

So you've got this balance.

How can a tyre do both things well?

So that's what I spend most of my life trying to worry about, how to do two things that are completely different at the same time.

It's so interesting.

I did a show called World's Most Dangerous Roads, where we had to do some really terrifying

off-road driving.

And it was the first time I'd learned anything about that.

But why is it World's Most Dangerous Roads?

Why did you go off-road?

Well, this is it.

I wouldn't have done the show if I did the show thinking, How dangerous can a road be?

They had us driving through a river.

I had to drive through something called a gulch at one point.

I drove up a ski slope.

It was terrifying.

It's just misleading, then, isn't it?

It's misleading.

The world's most dangerous road is not a ski slope, is it?

I don't know.

But the first time I'd learned about 4x4 driving and how, effectively, you know, my point is,

I found it really interesting that, and it wasn't shown on camera, but our tyres were deflated down to about 10%

before doing anything really technical, so that our grip was exceptional.

But obviously, that was probably horrific environmentally.

We were talking there about the heat of rubber and the damage in terms of elasticity and I was thinking one of the most famous tragic stories of elasticity being lost is probably the Challenger story where you had these, for those who don't know, there were O-rings which basically were meant to

that they would expand and contract when Challenger was leaving the

seals, the seals in the solid rocket boosters.

But they would basically that they make sure the tiles stayed in place.

But actually, what happened was on the launch day, it was so cold that they lost that ability.

And that's kind of how it was proved in the committee they did, where Richard Feynman popped in an O-ring into a glass of ice water and then pulled it out and went, Look, you see it cracks now.

So, you know, how firstly, I don't know how much you can tell us about what went on there, but also what happens again in these different temperature situations where these risks arrive and the loss of elasticity.

Yeah, it's related to

the colder it gets, the less energy the molecules have and the less able they are to move basically.

And there's a lot of materials that have a property called the brittle to ductile transition temperature.

Why is that funny?

It was like in a way, it was the way that you

was so perfect.

So let's just have that one more time so we can all use this at home.

The brittle to ductile transition temperature.

Deductile.

Deductile.

Brittle-deductile.

Brittle-to-ductile.

Brittle-to-ductile.

Sorry.

Brittle.

I'll say it a third time.

Brittle.

Jeez.

Brittle to ductile transition temperature.

And essentially, what it is is that when you cool a material down, it becomes brittle.

It's more likely to break, it's more likely to snap.

And again, it's not just rubbers that have this.

Metals have a brittle to ductile transition temperature as well.

And it's thought that actually, for steel, for the sort of steel that the Titanic was made out of,

one of the reasons that the Titanic disaster was so bad was that, as we know, they were going through very cold water, so cold some of it was frozen.

And the steel on the hull of the Titanic was below its brittle to ductile transition temperature.

And so it was a brittle material.

It wasn't like a car when you hit it and it deforms.

Instead, it just smashed like glass.

There's one reason why it was so catastrophic is because the steel was so cold.

And I would think that the challenger disaster has a similar kind of mechanism.

So, on the same sort of level as that, that's Titanic

with trampolines.

So, when it's cold, the springs break a lot more often.

So, when we're jumping, we'll have a spring or two that I've got a whole trophy cabinet full of broken springs throughout my career.

But yeah, so that that explains why on a cold day the trampoline one feels harder and the the scientific term harder or softer trampolines.

So if it feels really hard, basically you're you're not depressing the trampoline very well, it feels really dead and you can't really get any bounce from it, but also the trampoline springs just break.

Wow.

And is that quite a subtle temperature difference?

'Cause a cold day can't be that much colder than a warm day.

Yeah, I guess it's a subtle temperature difference, but I can feel the difference and most people jump in, but also it's our bodies as well.

If we're not as warm as we're used to

and you're getting cooled down quickly, then it that also you feel in more pain.

You don't feel like you're as springy and jumping as high as you would like to, but the trampoline is not giving you anything either.

Because I think in a trampoline movie, like a kind of disaster movie, I would love to have that scene where you go, God damn it, we've got to close down the trampoline.

It's brittle, too ductile, you know, or something like that.

Is that part of the because it would seem that you would just say, okay, well, the response to that would be, can't we just use a kind of steel or whatever that make the springs out of something that aren't sensitive in that way around freezing point?

But is that part of the compromise or the payoff with the material?

Exactly, that's exactly the point.

I do a lot of work with motorsports tyres.

You want to imagine a Formula One team, they want to make sure they get the quickest lap time.

They don't really care about generating abrasion debris and stuff like that, they don't care about the fuel efficiency, they care about grip.

So, if you're trying to design a Formula One tyre, you make it so they've got this transition that's a very high temperature.

So, the tyres actually have a glass transition or brittle to ductile transition of around zero degrees.

It's kind of a composition though, isn't it?

You can say brittle to ductile faster.

We can just say BT DTT.

I'm going to call it the glass transition from now on, okay?

This is somewhere between My Fair Lady and Sesame Street today, now, isn't it?

Just as an aside,

glass, why is it called a glass transition?

So it's called a glassy transition because above TG, if you've got a rubber band, and I've got one here that you can stretch, it stretches.

If you draw the it, Tg is the glass transition temperature,

or the brittle to ductile transition tests.

If you take this rubber band below its glass transition temperature, which for this is minus 70 degrees C, so I'd have to have a bucket of liquid nitrogen or something like that, and I stretch it, it would break.

Similarly, when I'm working with Formula One tires, I had them delivered to me once on a cold morning.

And the man who delivered it was the typical delivery man, and he says, I've got this delivery of new tyres for you, you're going going to do some work on.

And he threw them from the top of the roof of his truck and it was about minus five outside and they all broke because the Tg of Formula One tyres is above the temperature.

So they were already brittle.

So when you're choosing a particular material, developing a particular material, you have to consider very carefully the environment in which it's used.

Exactly right.

So you've got to pick a material that's got a low glass transition temperature.

So if you're doing something like the O-ring seals for the challenger and you know there's a potential for it to come into contact with liquid oxygen or liquid, the fuel, the rocket propellant, or whatever that it came into contact with, you need to make sure that that O-ring will be able to survive and still be elastic at the temperature it's operating at.

And in the case of the Challenger, it wasn't.

Well, it was very famous, wasn't it?

Because it was a cold day.

It was a cold day, and that also exacerbated.

There was a leak as well as a consequence of it being a cold day, I think.

Yeah.

I've got to ask you, James, you've got, because we're getting near the end of the show, you have a huge rubber band in front of you.

I do, but it's a visual gag.

That's absolutely fine.

Our audience have fantastic imagination.

And Jess will describe

it.

Last time you had to describe paper, scissors, stones, didn't you?

Yeah, I wasn't great at that, so.

Oh, I think you were excellent.

We're going to work on it for this.

What we've got is a big red rubber band.

And don't let go.

Am I allowed to walk off?

And I'll go off mic.

Yes, okay.

So it's the sort of band that I would use to do physio on my arm.

It's that kind of.

use your good arm, not the one that's broken already.

Mind you, I really need the one that's

oh my gosh.

He's gone so far away.

I'm not gonna get into the audience.

I'm nervous.

Let's go into the audience.

Oh, no.

Yeah.

Okay, I'm gonna let Brian hold it.

I don't want to be responsible for twanging the body.

Not the face, Brian.

Not the face.

The audience is so big.

Okay.

Okay, it's now as long as the room.

So right to the back of the theatre.

Oh, my crumbs.

James is now right at the back of the theatre.

James is at the back of the theatre.

On the counter, three.

Two,

one.

And today,

the memory of

James.

And that's how she died.

So that was quite frightening, actually.

And I think we have a...

I'm not sure we did the risk assessment.

So

what happened there, other than something very frightening that scared half the audience and leaves us open to legal

so as as was being described this is a rehabilitation band you've stretched it you've stretched it a long way because it's it's a long band and you've aligned all the molecules and you've got it to a point where it's it's reaching a quite a high stiffness and as a consequence when you let go it goes back at the wave speed so that's determined by the elasticity of the material so it goes back really fast and makes that noise and you were very confident that it would go back in a straight line straight straight back to you, I think, because just for everyone at home, that went straight down the aisle.

I was too scared.

That was very close to people.

Because it looks like, I'm going to use real scientific language now.

It looks like quite a flappy material.

That did.

That looked quite chaotic and like it could have thwacked an audience.

It didn't, though, did it?

Not today.

No, I've done this experiment before.

And what?

Not in the edit anyway.

Two.

But what was interesting to me is it was quite slow.

It was a lot slower than I imagined, which, as you said, is the wave

speed.

It's the retraction wave speed of the material, which is determined by the modulus.

And because it's soft, the wave speed is relatively slow.

So, is that the speed of sound?

It's the speed of sound of the rubber band, yes.

I think probably the reason I and many other people were nervous about it is they go quick.

Don't they?

So,

not if you stretch them 20 meters.

I mean you're right I mean if you stretch it far enough rubber is a mysterious material cis polyospin is a mysterious pig it's to reinforce trees that's what it's for so in the tropical jungle that the tree has got this tree sap in its bow in its bark and that's what we tap to make natural rubber it actually when you stretch it a long way crystallizes

So the material then becomes tougher.

So if it's in a really big storm, the rubber is self-reinforcing and makes itself tougher, which is why evolution has done such a great job at making rubber as strong and tough as it is.

In terms of, we do hear about the, you know, that there ultimately won't be enough rubber for the demands of the world.

So, James, you know, where do you hear that?

I've heard it, I've never heard that.

Is that true?

So, there are a number of risks here.

First of all, natural rubber is indeed a natural resource, and so you could think that's really good, it's sustainable.

But, of course, it's grown in places like Malaysia or Indonesia or Thailand, and they deforest vast swathes of tropical rainforest to plant a monocultured source crop of hever Brasiliansis trees, which are all genetically identical to each other.

So, from a biodiversity point of view, natural rubber isn't that sustainable.

They're clones, they're all clones, they're all essentially cloned from the same tree, which makes them very vulnerable to things like viruses.

So, if you have a virus that hits it and wipes out the whole of Malaysia or Thailand, we have a real problem.

So, we clearly have a number of issues there.

About 18 million tons of natural rubber are harvested every year.

If you think about what we do at the end of life with all that natural rubber, things like training shoes that are made out of it, we landfill them, or we burn them, or we don't recycle them.

We don't really properly recycle tyres either, globally.

So the aim here will be to make sure that we could create a renewable use of that material.

So recycling of natural rubber is hugely important.

There is an awful lot of other rubbers that are synthetically produced.

So you've got synthetic cis polyisoprene that you can have, which is available on the market, made from gas sources.

And actually your car tyres are mostly made out of styro and butadiene rubber.

And so that is also a huge amount of material that's been taken out of the earth, it's converted from oil or gas stream into producing rubber.

So yeah, that's not sustainable either.

So there's a lot of effort putting into thinking more sustainable sources for these materials and recycling these materials at the end of the life.

One of the things that we haven't really talked about is, in terms of elasticity, is why men wear those really horrible, really, really tight jeans that don't go as far down as the ankle and then no socks and tassel-y shoes.

Is there any way we can get rid of that?

Does anyone know?

I don't like it at all.

They're not sustainable, are they?

No, they're not sustainable.

No.

We're almost talking about a world without rubber, but then we're also talking about that which is not rubber.

So explain what biomimicry, what we see there.

Biomimicry is my favourite concept in materials engineering.

And it's basically, as we've already said, there are some amazing natural materials, natural rubber, bone, good ones,

that

do fantastically for the job that they've been evolved to do.

And because they're so great, things like underwater glues and spider silk that can stretch super, super long and still be strong and flexible, we are now looking to nature to see, oh, okay, can we make a synthetic spider silk in the same way that we said, oh, can we make synthetic natural rubber?

And this is this concept of biomimicry.

And I just think it's genius because why do all the work that an evolution has done?

And can we just copy these structures ourselves?

I was walking down the street the other day and I saw it almost looked like a spider was flying because it was just hung it was so far across the street and trying to work out where is that attached right I can see the other side I can see it's attached to that bush there.

But that to me, you know, again, as you say, to this, to look at nature and go, well, that is more remarkable than the human imagination is capable of at this particular time.

Yeah, and the depressing thing is that these materials are often so complicated and so

well made that it's actually really, really hard to engineer stuff ourselves that does even half the job of spider silk.

I found some ways that we are trying to make spider silk ourselves, and it's basically to do with just genetically modifying other bits in nature that can do it for us.

We can't really do it in a vat in a lab yet.

And the things that we've genetically modified are silkworms, okay, that's a boring one, E.

coli, and goats.

Goats?

Yeah.

Well, the spider goat thing.

Yeah, the spider goat.

So, hang on, so we're we're genetic.

We're implanting the genome of spiders into goats.

Yep, and it's I really hope they've called that goat Peter Parker.

Yeah.

Perhaps if Robin sees one strung strung up across the

goat.

Imagine that.

It's like a Ray Harry Hausen movie.

A goat right in the middle of a web.

I just want to bring Brian, is there anything that you think you've heard today about the science of elasticity, which thing that may well lead to a change in technique for the next gold that I'm going to get?

I think stuff we've already known about the temperature of the trampoline and trying to warm up the body in the right way so that we can get the full amount of power.

I can't get over how does the goat spinning a web?

Really?

That seems waving.

You've got to tell them where it gets out of the goat.

How does this work?

No.

It's in the milk, guys.

I can milk spider silk from a goat.

And with that, you know when you find

a fly in your goat's cheese, you know where that goat has been.

Jess, do you feel it's helped you in terms of now that you found out from your own experience the elasticity of your bones?

Do you feel that if we'd done this show beforehand, this whole malarkey would never have happened?

It would never have happened.

And I would have unbreakable bones because I'd have already been drinking goat's milk.

Why goats?

Well, we'll be covering that in the next week's episode, which is called Why Goats?

So join us for the Infinite My Cage.

Why goats?

Why do you say I've got to get this spider gene and put it into into something?

I'll put it into a goat.

Why?

Because there's somewhere for the silk to come out.

I'll tell you what, let's write Charlotte's Web 2 and see where we get to with that.

Billy's Web.

So thank you very much to our wonderful panel, James Busfield, Anna Poshaiski, Brony Page, and Jess Fostercube.

Now,

that audience you can hear just there, there, well, we ask them a question, and our question is: what is the best use of a rubber band?

What have you got, Brian?

DIY dental floss

for both the innovative and dangerously optimistic.

This one for Katrina, I could think of something at a stretch.

What have you got, Jess?

To improve your underwear, because thongs can only get better.

And with that, what is the best use for a rubber band?

Ping it as often as you can, because

pings can only get better.

To upgrade a guitar, because strings can only get better.

Next week, we will be joined by a giant sloth, a dodo, a woolly mammoth, and British Rail.

Yeah, there's correct, because we're going to be discussing bringing the extinct back to life.

I used to love it, actually.

Class 77 on the wood headline.

Right, now I know that this being radio form, some listeners will understand that reference.

And so we leave you with this question: What is the link between the Class 77 locomotive and the planet Jupiter?

Answers on a postcard, please, to Brian Cox, Multicoloured Swap Shop, BBC TV Centre, London, W12, 8QT.

Goodbye.

Goodbye.

In the infinite monkey cage without your trousers in the infinite monkey cage

Till now nice again Nature

Bangs Hello, hello and welcome to Nature Bang I'm Becky Ripley I'm Emily Knight and in this series from BBC Radio 4 we look to the natural world to answer some of life's big questions.

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And what can an octopus teach us about the relationship between mind and body?

It really stretches your understanding of consciousness.

With the help of evolutionary biologists.

I'm actually always very comfortable comparing us to other species.

Philosophers.

You never really know what it could be like to be another creature.

And spongologists.

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Are you a spongologist?

Well, I am in certain spheres.

It's science meets storytelling with a philosophical twist.

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So if you want to find out more about yourself via cockatoos that dance, frogs that freeze, and single-cell amoebas that design border policies, subscribe to Nature Bang from BBC Radio 4, available on BBC Sounds.

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