Cornflour Goo

by Deb on October 1, 2010

Mixing Goo

This probably wins as the simplest chemistry experiment you can do with little kids.  And the most fun!  Cornflour goo with real corn is amazing stuff, just add water for strange things to happen.  Make sure it isn’t wheaten cornflour, White Wings makes a corn cornflour.

Start with some cornflour in a bowl, add a tiny bit of water and mix.  Be careful, it’s a bit like icing sugar – add about half the water you think you’ll need!  Having trouble?  While you’re mixing it’s all hard, but when you pick some up it melts on the spoon?  Try some other things:

Making Goo

  • Punch itPouring
  • Run your fingers through it slowly
  • Run your fingers through it quickly
  • Drip it off the spoon
  • Flick the spoon
  • Stir quickly
  • Squeeze some in your hand
  • Hold your hand flat and let it drip off

Basically if you get the mixture right, when you do something quickly it will act as a solid, when you do something slowly it will act as a liquid.  Running your fingers through it is very strange, you can feel the gluey or plasticky lumps, but when you try lifting it you can only see liquid.  Even better, it dries quickly and can be stored, when you want to play again just add more water.

It is safe for all ages – it’s just cornflour and water – and even babies and little ones can get in there with their fingers and have a ball.

What’s happening?

Most mixtures we deal with every day are called stir-thinning, which means they get thinner and easier to mix the more you stir them.  Think about cake mix – it starts fairly stiff but becomes more liquid.  In most of these liquids the tiny bits that make them up are smooth and rub past each other, something like this:

stir thinning
Some mixtures like cornflour are stir thickening – as you stir them quickly they get thicker and stiffer, but stir them slowly and they are runny.  They are also called non-Newtonian fluids.  Sand is another stir thickening mixture, think about standing in the sand at the beach.  As you stamp down on it the square sand particles lock together and force the water out making it dryer and stiffer:

stir thickening quick

But when you stir it slowly the particles have time to settle and move easily:

stir thickening slow

More?

There are lots of fun YouTube clips of people running across pools of cornstarch, here is just one from Mythbusters.

Definitely have fun with this one!

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{ 11 comments… read them below or add one }

Cass October 1, 2010 at 11:09 am

My favorite of all your blogposts. I can’t wait to try that one at home. I even think an older kid could try and replicate the myhtbuster experiment in a small wading pool.
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shar October 1, 2010 at 3:10 pm

I have been making ‘goop’ for years but didn’t understand what was really happening with it. A really interesting post – thanks so much! BTW, when resources have been tight I have added boiling water (and stirred in very quickly) to some of the goop at the end of a session to make finger paint base or paint extender for the next day. It dilutes the pigment of the paint a lot but OK if the process of painting or finger painting is the objective rather than the picture at the end :)

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Lisa October 3, 2010 at 2:04 pm

I don’t know who had more fun doing this – the kids or me! It was a great to be able to explain to my 3yo how it worked when she asked too. Thanks Deb!

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Kelly B October 5, 2010 at 4:54 pm

Another goop play. I REALLY am meant to do it this week. Love it!
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cathy@nurturestore October 6, 2010 at 3:24 am

I think goop has such a mysterious texture to explore – and as you say it’s a great messy play activity for babies. Hope you’ll come and share this on with us at the Play Academy on Friday. Cathy :)

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amandab October 7, 2010 at 10:07 am

Thank you for the diagrams and explanation, as although it was fun to play with I really should have spent more time talking about it when we played with it. Now, armed with this, it must be time to play with it again :)

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Colleen - Sunrise Learning Lab October 8, 2010 at 4:35 pm

Very cool! Thanks for sharing! We have made something gooey kind of like this, but it is more like slime. Thanks for sharing the Mythbusters clip, too. We are big Mythbusters fans here.
Have a nice weekend,
Colleen:)
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Marita October 10, 2010 at 8:00 pm

Ah Ha! I think you may have just pinpointed my problem with home made moon sand – I used wheaten cornflour. :D Now the weather is warmer and we can experiment outside I’m willing to give making moon sand another go too :D
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Christie - Childhood 101 October 11, 2010 at 10:17 pm

I was just writing about goop myself today :) I have enjoyed it with many, many preschool aged children whilst never really understanding how it works… now I know LOL
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Skyebie April 9, 2011 at 10:12 am

Mine didnt work very well

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Deb April 9, 2011 at 10:26 am

I have two possible suggestions, check it was genuine corn cornflour not wheaten cornflour. Some things are sold as cornflour because they are very fine, but they are really from wheat.
And look at how much water you’re using. You need much less than you expect, about half as much water as you have cornflour.

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