Saturday, 6 January 2007

Primary Science: fun things to try at home. Number 1: Bouncing Liquids and Walking on Water

Here is a really great thing to try at home (with or without children).

You will need:

a bowl
cornflour or custard powder (but not instant custard)
water
an egg cup
a spoon
What to do:
1. Put 8 egg cups of cornflour or custard powder into the bowl.
2. Add 3 egg cups of water.
3. Stir gently with the spoon, adding more water if it's too dry.
4. Stir it quickly and see what happens!
5. See if you can shape it into a ball and bounce it on the countertop!
What you have made is called a dilatant liquid. You should find that as long as you handle it quite roughly, it will behave like a solid, but when you are too gentle, it turns back into a liquid and drips through your fingers!

If you make enough of the stuff and have somewhere to put it, you can actually run across the top of it. Be warned - if you stand still, you'll sink, so don't make it too deep! See here for Jonathan Sanderson's article 'Walking on custard' Jonathan's Web Pages can be found here

The Science Bit
Cornflour and water combine to make a non Newtonian fluid. See here for the physical properties of chemicals. The viscocity (thickness) of non Newtonian fluids is affected by shear forces (stirring) as well as by temperature. This leads to some pretty odd behaviour. Dilatant fluids get thicker the more you stir them, whilst thixotropic fluids get thinner. Examples of thixotropic fluids are ketchup, and non-drip paints. These become runnier the more you stir them which is why ketchup comes out of the bottle more easily if you shake it. When you stop stirring or shaking these liquids, they thicken again.

And here is a video I found showing how you can 'Walk on Water'!




Notice: I cannot find the creators of this video to ask permission. If it is yours and you would prefer I did not use it, or would like me to put your name to it, please email me. Thanks.

Noticia: No puedo encontrar la gente quien han hecho este video por conseguir su permiso. Si esto es lo suyo, y quiere usted que no lo utilizo aqui, o si quieren que su nombre puesto, por favor, mandame un email. Gracias.

3 comments:

bourbouli said...

An ancient Greek philosopher once said : "The more i grow older, the more i learn" and another one said : "One thing i know, i know nothing"

Maybe you have spiritual Greek roots (due to your moto in this extraordinary blog).

Keep writing in this beautiful e-place. You added another fan

Jonathan Sanderson said...

Thanks for the links, Lisa! ScienceDemo.org is sort of sitting around waiting for a few of us to have time to kick-start it; it being linked to gives us a bit of a reminder to actually do something.

Also, welcome to the blogosphere (whatever that is...). Stick with it, it becomes addictive - but make sure you enjoy the writing process. You can't guarantee an audience, but if you're having fun throwing words together, who cares? If others drop by, that's a bonus...

(or maybe I'm just in denial, and 'real' bloggers do it for the readership? :-)

hesitant scribe said...

Jonathan - you're more than welcome for the links! I love science that's accessible to the lay addict like me!

As for the writing, addicted to that too, from a young age, so the blogosphere is wonderful, and if I get an audience - well that would be wonderful too!