Not the two things with the most obvious of connections I agree, but bear with me.
Spare a thought if you will for all of those body parts that are going to get bashed, smashed and generally knocked around for the next few weeks. I am of course, referring to the hands, shins and other, more delicate parts of the world’s top footballers as they endure the many matches during the World Cup that starts this Friday.
So what have they got to do with custard? Custard powder is mainly cornflour and this is an ingredient of the infamous great, but messy, activity. Very simply, you mix some cornflour with water to make a thick paste. If you gently pick some of this viscous liquid up it will run through your fingers but if you hit the mixture, your fist will simply bounce off, as the impact makes the liquid behave like a solid.
This cornflour-water mixture is classed as a dilitant material because it’s apparent viscosity increases with increased stress. This happens because applying a force to the mixture pushes water out from between the cornflour particles so they stick tightly together. It seems that this experiment is a popular past-time by the shear amount of videos dedicated to it on youtube -- you can see people walking on it and wierd shapes produced when it is placed on a loudspeaker if you so wish.
So – this brings me to football. A British company called d3o have produced a smart material which sportswear specialists Sells have used in their range of protective clothing for footballers. The material is flexible under normal circumstances but goes rigid when under impact – just like the cornflour mixture. This is very useful in one of its applications – goalkeepers gloves, as the flexibility is vitally important when stretching for the ball and gripping it but stiffens to protect the hands when stopping that vital penalty. It is also used in shin pads that can reduce the amount of force to a player’s leg by up to 70%. To see the material in action watch the video if it being tested below.
Looking at this material and its many applications (it is also used for things like protective ipod covers and even bullet-proof vests) would be a good example of a smart material to show during a lesson to GCSE students; but understanding how it works at the molecular level could be used with a KS3 class.
The two slide PowerPoint I have designed shows this. Students who have been studying the particle model of solids, liquids and gases can predict how the material works as a way of applying their knowledge. They might not come up with exactly how it works but as long as they can explain how their idea gives the same change in property then that’s good enough.
How it works is pretty similar to the cornflour mix as it is another dilatant material. Under normal circumstances, the molecules (which are polymers) can flow and move past each other freely but on impact, the form cross-links with each other, transforming the material into a stiff-state. As soon as the impact is over, the links break and it reverts into its fluid-state.
Voila – the connection between custard and football -- told you that I would get there in the end!