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Experiment

Cornwall College Camborne students achieved the tricky feat of walking on water for National Science and Engineering Week earlier this year.

National Science &#38; Engineering Week is an annual excuse to throw the laboratory doors open and invite people into the workshop as experts in the subjects share the exciting world of STEM with the masses. Supported by the British Science Association, the week typically sees some interesting and entertaining experiments and Cornwall College is no exception.

Keen to do something on a grand scale, science graduate and Cornwall College STEM Project Manager Alex Ledbrooke disappeared into the storage cupboard and emerged with a few hundred kilos of cornflour, a paddling pool and the news that he would walk on water. It’s a well-known trick that many have witnessed on a small scale and many have seen on internet videos but few have actually done themselves.

By mixing cornflour and water together in the correct ratio (see

Cornwall

College STEM Volume 1, Part 1 for details) a non-newtonian liquid can be created. A Newtonian liquid is a fluid whose shear stress is linearly proportional to the velocity gradient in the direction perpendicular to the plane of shear. That’s a long way of saying, Newtonian liquid continues to flow no matter how hard you push, splash or stir it. A non-newtonian fluid is one that doesn’t follow Sir Isaac Newton’s laws of physics in that as the shear (pressure) on the fluid is increased, its viscosity temporarily increases. Gently stirring a bowl of non-newtonian liquid would present you with some resistance. Giving it a whack would feel like punching a brick wall!

What’s happening in the liquid? The cornflour particles are suspended in the water. Under low pressure, the particles will flow over each other but, as the pressure increases, the water between

each particle is displaced

leaving the particles to bump into each other. Do this with lots of pressure and the water displaces very quickly, the particles all collide and the temporary solid properties of the fluid appear. So, if you take a paddling pool, add a

few hundred kilos of cornflour, add a lot of water and mix with an industrial size mixer you have the potential for a Big Experiment. Students at Cornwall College’s Camborne campus were treated to a hands-on lunch break science lesson in their common room and after talking about the science behind non-newtonian liquid were invited to attempt the impossible and walk on water.

As long as the pressure is maintained – in other words you keep running - the fluid will act like a solid and support a person’s weight running across the pool. Anyone who was too slow would sink into the pool of non-newtonian liquid where the opposite happened, and it became very difficult to escape as the fluid behaved like a solid as pressure was applied to legs to haul them out of the mix. The only way out was very slowly and very carefully!

The Big

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