You might have seen the Big Bang Theory guys doing the cornstarch and loudspeaker experiment. We thought we’d go one better by making a giant version using 10 kg of maize starch, a paddling pool and an industrial shaker. What was the biggest cornstarch monsters we could make?
The water and cornstarch mixture is a non-Newtonian fluid, and this means it behaves very oddly. You can pick it up, and provided you keep moving it about so it’s under stress, it stays solid. But as soon as you let it rest, it oozes back into a liquid. In this photo you can see how the stuff resting on the hand is behaving like a liquid, whereas the “stalactite” has cracks in it, because the stress created by gravity changes the cornstarch’s properties.
We found that low frequencies worked best, the video was made with the industrial shaker working at 20 Hz. But the real key to getting this to work was to make sure the paddling pool moved a long distance up and down. Our industrial shaker was limited to about 2.5 cm of displacement – more would have been even better.
Jogging the paddling pool up and down puts the mixture under stress, allowing these weird ‘stalagmites’ to grow