Lecture 2: The Trainer That Ran Over The World

The trainer is a miracle of modern science. The average pair lasts just six months, but in that time, they will have run 3,000 miles, absorbed 400 litres of sweat and withstood 400 tonnes of impact. How they survive this battering is down to some miraculous chemistry that lurks beneath their flashy skin - a hidden world of impact cushioning gel, moisture absorbing insoles, and breathable foot-hugging coatings. So tune in and explore the chemistry that propels us around the planet.

Professor Tony Ryan
[Tony jogs into the lecture theatre.] So today I'm going to talk about something we all have to do in our lives and that's travel.
Transporting yourself somewhere today can be done pretty much any way you want, but perhaps the simplest method is using the power of your own two feet.

Now what you're wearing on your feet isn't always the fashion accessory you think it is.
Often there's lots of excellent engineering in there.

So, I have some special trainers on. In fact they're so special I can show you what's inside them. [Tony takes one trainer apart.]
So on the outside are the laces and often they're quite high-tech, with the loads they need to take, and then there's the tongue and that's padded so it doesn't dig into you - and then there's the insole and for me, this is especially important, the insole's got special chemicals in so that it doesn't pong too much - [laughter] right.

And then there's foam here and this stiffening bar and a different foam and an air bag.

So we can see this air bag and these special devices that stop it from collapsing.
Now there are subtle differences in every trainer, depending on its design and let's start from the bottom.
It's the sole that's important.

[Footage of climbers on overhead screen.] Now we took some VT. tape of the lads out climbing last Saturday. In fact Eric's one of them, he's sat up in the back and he very kindly fetched his climbing boots in.
Actually those boots there are mine and I don't know whether they've slipped the piece in where I actually fall off, right.

And why did I fall off?
Well I fell off because the grip didn't work.
So to help me take a look at grip we're going to need some volunteers and those volunteers all have to be fifty kilos in weight and have size 5 feet.
Oh, look at all those hands go down! [Laughter]

And where are the six hands that are going to stay up with the right sized feet over here?!

[Group file in.] ... Come here.
What's your name? ...
Right, pleased to meet you.
I'd like you to stand on here.
[Girl steps onto tilting table.]
And what's your name?

Can you just use that handle to move her up in the air please.
No, you don't have to do it too quickly, keep coming, up we go, up we go.

What angle are we getting to down here?
We're up to ten degrees, whoa, and who's going for a slide![Laughter]

Down she comes, well done!
Thank you very much indeed.

[Applause.]

See, those bowling shoes were on the same material that's used to make non-stick frying pans, so you wouldn't expect her to go very far, would you, in terms of the height and the next pair, what's your name?

Pleased to meet you, come on, let's get you on this grassy slope here. [Second volunteer steps on to the astro turf.]
Well it's not a slope yet, but it will be soon.
OK, on you go.
These are your trainers, aren't they? [Yep].

And what's your partner called? [Rebecca].
Rebecca, come on, out you come.
So I'm going to move the handle up and down.
And up she goes, twenty degrees.
Do you want to just stand round there and make sure she doesn't topple off?
That would be a big help. Thank you.

So don't lean on her, just use her for balance.
How are you feeling at thirty degrees? Good?
Whoa, off she comes, about thirty five!
Well thanks a lot, girls [applause] - you have thirty-five degrees there.

[Third volunteer comes forward.] Oh wow, but I recognise those shoes, they're a pair of rock climbing boots like these, they have special soles, designed for this rough surface, so out you come.

What's your name? [Nikita].
Nikita, come on, on you get.
Hold my hand as you get on, because you know they're not very stable, these.

Turn round towards me, Nikita, don't worry, it's going to be fine, just move back a touch.
And your name? [Rachel].
Rachel, look, I'll tell you what we have to do.

We have to move it up and down, gently like that, OK?
Right, you can do it this time.

Just down there, move back a bit.
You feel great, don't you! [Yeah].

You're not going to fall off at all, are you!

This is sticky rubber.
What's happening is it's been bent by all the protrusions that are on this sandpaper and that's there to simulate the rock, OK, keep going.

What angle are we at now?
Thirty-five, forty, you want to fall off, but it's not because you're losing grip, is it?

Let's stop there for the moment, just come, walk down a little.
I'd like you to turn round ... like that, just balance on your fingertips.
OK, come on, keep on going.

All the way up, all the way up.
Does that feel good? [Yeah].

I'll tell you what, Eric'll take you out rock climbing next Saturday if you want to go! [Laughter.] [OK then.]

Alright.
And where have we got?
We've got all the way out to fifty degrees.
Thank you both very much indeed. [Applause.]

[Tony stands behind table. Assorted trainers lie on the table.] Let's say the soles of your shoes were made out of treacle.
Now, you'd stick, wouldn't you, if you had treacle on your feet, but when you were tilted up, what would happen is the treacle would just slide, so the forces making you grip are a combination and they're a combination of the two surfaces and the rubber itself.
You see we'll find that this contact between rubber and another surface is common to nearly all forms of modern transport.

[Footage of rubber plantation.] So, natural rubber is harvested from trees. I've got some here.
It's that milky fluid you can see dripping into a cup, so here's rubber latex.
That contains the material that eventually makes this.

And the American Indians were the first people to start using it.
What they did was they learned how to make the first wellington boots, by dipping their feet in there - right, because the polymer goes onto your foot and, and the latex dries, so you get rubber, like this.

[Tony holds up a polymer chain.] Now the rubber's a polymer chain and it's all tangled up.
That's how it wants to be, all tangled.
And what happens is, when you stretch it, you untangle the chains and then when you let the tension off, then the chains re-tangle again.
[Shot of a bowl of spaghetti.] In fact, it's just like this bowl of spaghetti.
In here are a load of chains that are all tangled up.
So if I dig my fork in and lift - I don't just get one, I get all of them.
But you see, when I let, when I let go, it doesn't spring back to exactly the same place.
Some of the chains slide past each other.
So you get what's called a permanent deformation.

Now if your shoe soles had rubber on where the material could slide past, that would be just like having treacle.
It would just slip.
It wouldn't be any good for you at all and you don't want this in your shoes or a car tyre.

And vulcanisation, the cross-linking of rubber was invented in 1839 and that started the whole industry around rubber.
And vulcanisation creates a tangled web by joining the strands of spaghetti together, so that when you stretch one chain across the join to many other chains, you have to stretch them too.

So they all jump back into exactly the same shape once you take the tension off.

Now I'm going to need four volunteers to help me.
These two lads down here had their hands up pretty quick, the girl in the black 't' shirt and the young man in the blue, is it a blue shirt, blue fleece? OK, we'll use you four.
I'll just nip round.

[Tony stands with the four volunteers.] I want you to, right, we'll take you two together, at the back here.
So I'll just stand there like that and you two together, further towards the front, facing the cameras, please, you come here.

I'm going to give you a snake, you're not frightened of snakes, are you?

Are you sure? [Yes!]

Not even snakes that are this big?
It won't bite, OK.
Now I want you to turn and face each other, just hold it there please. Good lad.
And I'm going to run round the other side of the desk, OK, you need to be a bit closer together, OK, a bit further apart, perfect.

OK, I'm going to run round the back - to direct what you do.
OK, so the front two, will you pull on the snake, how far does it stretch? [Children pull on 'non-stretchy snake'.] Not very far at all, OK, that's fine.

Right, you two boys at the back, can you pull? [Boys pull on 'stretchy snake'.] [Laughter.]

Pull, pull, keep pulling, don't let go, whatever you do! [Laughter.]

OK, you can come back in now.
Come, I'd come back in slowly, if I were you.
OK, give me back the snakes, thank you very much. [Applause.]

So, what happened when this straight snake got stretched was the molecules all got stretched.
So the molecules are all coiled up in the snake originally and then the molecules all stretched out and there were big lengths of chain between the links in the bendy snake and it'll store lots of energy, right.

But there's hardly any distance between the chains in this snake that's really hard, because there's hardly any chain to bend and stretch between the links.

So I know you've been flicking your rubber bands at me, right [laughter].But what I'd like you to do is take your rubber bands out now, so just put them on your thumbs, stretch them apart, OK.
So now what I want you to do is put it on your lip - [laughter] and stretch it on your lip - I'll see you later, right!
So stretch it on your lip. Feel it get warm?

Right, let it back in, slowly.
Feel it get cold?
Right, it's amazing that, isn't it.
It gets hot on the way out, cold on the way in.
[Graphic/simulation of rubber band on overhead videoscreen.] You see, inside the rubber bands are a big collection of jumbled-up polymer chains that are chemically linked together and when you stretch them out, they have to lose some energy.

You see they're dancing around, so the molecules are all dancing around and you stretch them and they actually can't dance that much any more.
And so they give you some energy back.
You feel it as heat and then when you un-stretch the rubber band, it gets cold, because, and it should be on its way back in now, the rubber band, the molecule, it goes from being unable to dance, to dancing again, but it needs to get that energy back and it takes it from your lip.

And what's weird about rubber is that it contracts when it gets hot and expands when it gets cold and that's not the way that things normally behave.

And it's this unique property that makes it grip the way it does.
You see it's not just the bottom of our shoes where grip's important.
[Videotape shot of Formula 1 cars on track.] If you're travelling at two hundred miles an hour, like these racing drivers, you want to be sure you're going to stay on the track, so you can see the car that these tyres came from and someone's going to come down and help me have a feel of these tyres. [Tony compares tyres in lecture theatre.]

OK, have a feel of this one.

Does it feel sticky? [Yeah].
Yeah, it does, does it feel very sticky? [Erm, no]. [Laughter.]

OK, very good!
Right.
And it's cold, isn't it? [Yeah].
Have a feel of this one.

Do you think this one's going to be cold? [No].
All right we'll open it up now.
Just take your hands off a moment.
What's your name, by the way? [Patrick].
Right, Patrick. OK, have a feel of that one. Wow!

It's warm and it's sticky, isn't it? It's amazing!
Do you think that's sticky? [Yeah].
Right, and why do you think they keep them under the hot blanket? [So you don't have to heat it up].
Right, so you don't have to heat them up when you go out on the race track.

Thank you very much, Patrick. [Applause.]

You see, the stickiness is because of the way we've put the cross links into the rubber.
Racing tyres don't last very long.
They could maybe get you down to the shops and back, if you drove like Eddie Irvine, right.
Normal car tyres are a little bit different.
They're a compromise between grip - whereas these are only grip.

These'll only last for at most a hundred miles, whereas the cars your parents drive, you need those tyres to last for tens of thousands of miles, especially if you're as cheap as me and you don't want to replace them very often, right.

So real car tyres, road tyres, they're a balance between grip, holding onto the road - rolling resistance, which is how much petrol you'll consume and longevity, which is how mean you are, right.

So we've seen how Formula One tyres and trainers are based on rubber for their grip and we know that deforming the rubber makes it hot - you know, your feet really do get hot if you're running.
That's because of all the energy that the rubber molecules are dealing with.

But what happens if your trainers get cold?
[table is wheeled in/Tony investigates liquid nitrogen container/dips rubber glove into container.] So, in here we have liquid nitrogen.
It's a minus a hundred and ninety-six degrees centigrade.
And here we have a rubber glove.

So, we're going to take the glove and cool it down, OK, it's changed, hasn't it?
It's not rubber any more. In fact, what I can do is ...[glove is crumbled up]... crumble it up, just like glass.

[Close-up shot of pieces on the floor.] So sometimes, this wonderful material behaves like a liquid and sometimes it behaves like a solid.
And in a few moments we're going to take a look at the differences between liquids and solids and why don't you all give me your rubber bands - now! [Laughter.]

[Children throw rubber bands at Tony.] [Applause.]