Have you ever noticed if you get a bit of custard on your hand, if you play with it,
it becomes very solid but if you leave it for a while it will drip off your hand.
Now this idea is known as a non-Newtonian fluid and has been studied by mathematicians
for centuries.
But new technology makes it appear that this, this clever little bit of fluid dynamics can
be used to save lives.
Now most fluids like water, oil, even air, are very well behaved.
You can write down a set of equations which will predict exactly what they'll be doing
at any point in time in the future.
But there are some fluids which don't conform to this perfect equation and these are known
as non-Newtonian fluids.
They have quirky properties that they change depending on what's going on around them.
Now one type is called shear thinning and this is ketchup, mayonnaise and paint.
Now have you noticed that with a bottle of ketchup that if you just turn the bottle upside
down all the ketchup is stuck in the bottom of the bottle but if you give it a good whack
suddenly you can get your ketchup to flow out of the bottle.
Now the whack that you give the bottle is changing the viscosity of the thickness of
the fluid of the ketchup and allowing it to flow.
It's the same idea with paint.
That's why you stir paint before you get going, you get it as thin on a paintbrush to go and
adhere to a wall, but as soon as it's on the wall it then thickens so it doesn't drip and
you don't get brush marks on the paint.
Now the idea of quicksand is exactly the same, so any mathematician whose looked into the
equations of shear thinning fluids will tell you if you get caught in quicksand you should
stay as still as you possibly can because otherwise any forces that you apply in your
movement to the sand around you will turn it into a liquid around you in exactly the
same way ketchup becomes liquid when you whack it on the bottom of the bottle.
Now at the other end of the spectrum are shear thickening fluids.
Now this is like custard for instance.
So instead of when you move custard, when you apply force to custard, rather than it
becoming thinner it becomes thicker and solidifies in your hand as you play with it.
Now this is all very well, it means that certain scientists can run over custard er in a swimming
pool and do all sorts of experiments like that.
But actually it has a much better application which has just recently been realised.
Now this is the same as that special science putty that you can buy from the science museum.
You can pull it, you can bend it, you can mould it, if you leave it to sit there it
turns into a puddle, it turns into a liquid puddle.
But crucially if you hit it with a hammer it will suddenly become perfectly solid and
shatter in to lots of different pieces.
Now it's this property of hitting it and it instantly becoming solid which allows you
to use these fluids in bullet proof vests for exempt.
Now if you can imagine a standard bullet proof vest it's very big, it's very bulky, it's
very heavy.
They weigh 12 kilos or 25 pounds, they're very difficult to move around in but if instead
you can get this fluid and stitch it in to the fabric of a bullet proof vest it can be
much thinner and much lighter but crucially it has the same properties of being able to
stop a bullet.
As soon as the bullet hits the surface it will immediately contract and solidify in
a thousandth of a second.
Now these bullet proof vests are just being developed at the moment, and are shown to
be just as good as the original ceramic ones in tests where they fire bullets at 300 meters
per second at the target.
But if you can imagine that there is a fluid which can be put in to the lining of something
that's strong enough to stop a bullet then it changes the way that we can make helmets
for instance in the future.
So if you imagine like a skateboarder or a snowboarder.
The helmets that they wear it sort of restricts their movement and they're quite big, their
quite bulky and also image is very important to people who are involved in these kind of
extreme sports.
So certain companies have started stitching this fabric into the lining of beanie hats
which work perfectly as crash helmets for skateboarders and snowboarders.
But also they've started looking into making ballet shoes with this material inside.
So ballet shoes for instance have had this same design for hundreds of years and famously
ballet dancers have terrible problems with going on point in these shoes.
But instead if you stitch this putty like lining into the bottom of the shoe it can
protect the dancer's feet beautifully and er and offer much more freedom of movement
in a much lighter shoe.
So bullet proof vests, beanie hats as crash helmets and ballet shoes, turns out there
is more to custard than just putting it on your crumble.
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