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Tuesday, 1 March 2016

Can Something be Both a Solid and a Liquid?

Can Something be Both a Solid and a Liquid?

Carrying on with our 'states of matter' theme we did some investigating into the question of 'Can something be both a solid and a liquid'. The students carried out a number of tests on a variety of common kitchen substances and made some interesting discoveries.

The first test was to see if the substance would pour from one container into another. Some did easily and smoothly while others were slow or did not move at all!

Tomato sauce was very slow
Cornflour and water was smooth
Shampoo was fast

Sour cream didn't budge
The next task was to push the substance quickly with your finger and then push it slowly. What did they notice? Was the 'feeling' the same or was there a difference? What was the difference? We came up with a huge range of desciptive words.

Some fingers became stuck 
Some fingers were just too tempting and had to be licked!
Could they stir it? Was there a difference if they stirred it slowly compared to stirring the substance fast? How could we describe that? Some substances became thinner the more they were stirred while others thickened. Why was that?

Shampoo became thinner
The cornflour mixture thickened

Picking up some of the liquids was a challenge. Why could the students pick up custard (in this case cornflour mixed with water) if it was done quickly but not able to pick some up if done slowly?

Some substances took the shape of their container while others sat in a blob or left air pockets not quite filling the containers. We needed to do some research as we needed more answers. 

Two main categories were introduced: Newtonian fluids and non-Newtonian fluids (based on the work of Sir Isaac Newton). Newtonian fluids can be moved from one container to another by pouring and will take on the shape of the container, just like the golden syrup and water we tested did. Non-Newtonian fluids are special liquids that can change when a force, such as stirring or squeezing, is applied, just like our sour cream, custard, and tomato sauce behaved. 

So the simple vote was yes: substances can act sometimes like a solid and sometimes like a liquid. Then the question was asked 'would heat affect how these fliuds behaved?' ...

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