Wednesday, 29 January 2014
Cornflour slime - one of my favourite non-Newtonian fluids
This activity is one for when you have enough time and patience to tackle a bit more of a clean up operation since, unless your small children are far better at following requests than mine, it does end up with slime covered clothes, floor and table. Not to try to put you off, because it is brilliant fun, but I also would keep this one well away from carpets.
The basic kit is really cheap and easy to get hold of. You will need cornflour, water and something to colour it with - food dye if you have it, but I've used turmeric or fruit tea before and they work fine.
The proportions are a cup of cornflour to half a cup of water, plus a few drops of dye.
You may need to help with stirring as the ingredients can be a bit tough to mix. As they come together you should start to notice the shear-thickening properties of the slime - the faster you stir, the harder it is to move. Slow right down and the slime moves much easier.
I have never met anyone who didn't embrace their inner child when faced with cornflour slime. It defies common sense in a really appealing way that encourages play and experimentation. In the picture of my two boys together you can see them both experimenting with pouring the liquid from a bowl or spoon to make a puddle, yet if you push the puddle with a spatula you can heap it up.
I'm obviously doing this activity with tiddlers, but if you have older children there's a whole world of fluid mechanics to explore with this simple mixture. You could also try finding out about other shear-thickening liquids such as quicksand or investigate their opposite numbers - shear-thinning liquids. There quite literally wouldn't be life as we know it without these, since blood is a shear-thinning liquid. This is a property of ketchup which explains why if you give it a good shake you can convince it to thin enough to come out of it's bottle. Toothpaste is another one - squeeze the tube and it becomes less viscous so it can come out, but then thick enough that it doesn't drop off your toothbrush.
If you have no idea about the science, it's still good fun and a chance to develop your child's language skills by describing new experiences. If you do know the science, don't be afraid to use whatever level of language you know by mixing basic descriptive words with the more complex ones. By exposure to complex language kids can surprise you with what they pick up, even if they don't know straight away what it all means you are priming them to remember the terminology in the future. It's also fun to hear the words 'non-Newtonian liquid' from a four year old.
Should your little scientist make the leap to ask 'why does it do that?', you can nicely evade any really technical attempts at explanation with the phrase 'nobody really knows for sure, perhaps one day you will be the person to find it out'. Ollie wants to be a crane driver and Toby just says 'choo choo', 'snake' or 'chocolate cake' to most questions, so I'm pretty sure they're not considering a future in fluid mechanics just yet.