OK, so unless you've got a really strange craving, most of us wouldn't eat Corn Flour (Cornstarch for our US friends). Nevertheless, this is one of the most cool things to play with, and you probably have it in your kitchen. It's a great thing to do with young kids, but if you're anything like our MD, you might well find it intriguing yourself.
If you haven't tried this, you really must. It's a great option for a wet weekend.
What you need to do is:
- Put some Corn Flour in a bowl
- Add a small amount of water and stir
- Keep adding a small amount of water and stirring as you go - at some stage you'll see something really interesting
As you add the water, it will be initially quite difficult to stir. Once you get to a consistency of a thick paste, you'll notice something strange - it will be very difficult to stir quickly, but if you stir it slowly, it's much easier. We suggest adding small amounts of water at a time, as if you over-do the water, you'll lose the effect. You can always add more Corn Flour though.
It's an example of a non-Newtonian fluid (yes, of the Isaac kind) ... A Newtonian fluid is one that you probably think of as a normal fluid, like water. With a non-Newtonian fluid, it's thickness (or viscosity) changes depending on the force applied. When you apply a force to a non-Newtonian fluid, it might become thicker (like the Corn Flour - we call this a 'sheer-thickening' fluid), or thinner (a 'sheer-thinning' fluid). There are some fun examples of this in real life. You may have seen some notices about 'anti-climb' paints. These are 'sheer-thinning' - i.e. when someone applies a force (tries to climb up somewhere), the substances becomes MORE liquid, and the intruder hopefully slips off.
With a 'sheer-thickening' fluid like this mix of Corn Flour and water, here's some things to try:
- Stir it slowly and it seems like a liquid. Try to stir it quickly, and it seems more like a solid
- Try to roll a ball of it between your hands very quickly (like plasticine). If you do it right, it will feel as if you have modelling clay between your palms, but as soon as you stop moving your hands, it will turn back into a liquid and drip away
- Try (carefully) punching it - it will feel hard. Push your hands slowly into it, and it will feel like a liquid again.