Non-Newtonian is both insanely cool, and something a young mad scientist in training can directly experience and play with. Cornstarch mixed with water is a shear thickening Non-Newtonian fluid.
Shear thickening is basically what it sounds like; the fluid thickens when shear forces are applied. The fluid thickens when you apply forces into the fluid. The most spectacular example of this effect is people running across tubs filled full of the stuff. Run fast enough and the fluid supports them, but stop or run slow enough and they start to sink into the fluid. Another cool example of shear thickening is to fill the cone of a speaker pointed up with the fluid. Then playing sound causes the fluid to do all sorts of weird things.
Even though larger volumes of the fluid lend themselves to spectacular demonstrations, you can do some really cool science experiments with less than a cup of corn-starch. My nephew was visiting on short notice and we were able to put this experiment together only on what I had in the house for cooking.
We mixed up a mixture of cornstarch to water at 35:65 by weight. That’s actually a bit soupy a mix, but it made it easier to work with for a longer time with my nephew. Next we covered a small speaker with plastic wrap. My nephew was able to use used a cotton swab to stir the cornstarch slurry in the beaker, then spoon it out onto the speakers surface.
Once the cornstarch was on the speaker we used a function generator to sweep different frequencies and waveform shapes. While driving at fixed frequencies let us feel differences in the fluid at different frequencies, and let us do better science, it wasn’t as interesting as just driving random sound. My nephew still thought it was cool – but I think I am going to do another run of this with him using a larger speaker and sound.
When we were driving the speaker we could turn the function generator off and on having the material in the speaker switch from acting like a fluid, to acting like a solid – which was cool for an 8 year old. What also worked was showing him how driving at different volumes and frequencies changed the viscosity.
Its hard to see in the picture, but with the shear-thickening my nephew was able to drag and lift the liquid around like it had a very high viscosity right up until it started acting like a solid and breaking. At which point it would fall back into the pool acting alike a liquid. Hard to describe, but a cool illustration of both viscosity and Non-Newtonian shear thickening.
All in all I highly recommend this for anyone wanting to show kids that science is cool. If you don’t have any of the electronics, you can mix up a small quantity of cornstarch and water in the palm of a kids hand. Then when you tap it, it turns solid for a moment. Not as cool as using the speaker, but fast and can show kids something cool in a few minutes.