Unlocking the secrets of oobleck–strange stuff that's both liquid and solid
arstechnica.com
arstechnica.com
"If you have enjoyed this book you might also enjoy the text Bartholomew and the Oobleck, by Dr. Seuss, ( New York, Random House, 1973). As Dr. Seuss explains, Oobleck "squiggles around in your fist like a slippery potato dumpling made of rubber." He doesn't tell you how to make it, so I will here.
How to make Oobleck
1. Take one cup of cornstarch. 2. Add some drops of green food coloring; Oobleck should always be green in color. 3. Slowly knead in up to half a cup of water.
Oobleck has some extremely strange, non-Newtonian properties. It flows like water through your fingers, except when you work it like dough—then it immediately assumes a solid consistency. Except when you stop kneading it, it turns back to liquid. If you strike it quickly with something hard, you can shatter it!
Like all Dr. Seuss books, Bartholomew and the Oobleck can be read and enjoyed on several levels. For example, One Fish Two Fish, Red Fish Blue Fish can be deconstructed as a searing indictment of the narrow-minded binary counting system. Software engineers can benefit from a sophisticated reading of Bartholomew and the Oobleck.
The world would be a better place if every programmer would just play with Oobleck occasionally. The good programmers would be more rested and refreshed and the bad programmers would probably get their heads stuck to the table. But always remember, no matter how lowly or exalted a hacker you are, you are a child process of the universe, no less than the disk controller, or the stack frame mechanism (explained at such length in Chapter 6)."
This book came out in 1994 so is dated now, but as you can see it's treasure!
Take a clear pie pan or dish. Add a quarter to half an inch of water, then a couple drops of food coloring, and slowly mix in cornstarch and observe how it behaves.
We found a ratio that was runnier than oobleck, but if you let it settle, the watery color and the cornstarch would separate a little into layers. You could then stir it and create all sorts of cool slowly moving swirls that eventually fade away.
We found you could even use 2-3 colors. The colors mix a little, but you still get different layers that create multicolored swirls when disturbed.
A piece of white paper under the glass dish makes it easier to see.
It surprises how few adults I encounter have any idea what I'm talking about when I mention it by name describing something behaving like a non-newtonian fluid.
For example recently I was telling someone how deceptively epoxy that seemed thick and extremely viscous while mixing will slowly but tenaciously flow through the tiniest of gaps in a mold or dams as if it were water. I've found JB Weld in particular behaves a bit like a non-newtonian fluid while stirring it up before application, seemingly solidifying more the faster it's stirred, then turns runny when still until curing sets in...
This seems backwards. Am I missing something?
I guess the bit you were missing is that the period when layers slide quickly over each other is (in my experience) very brief: typically the experience is your spoon almost immediately gets stuck and further pushing will break off chunks of oobleck, not push it aside.
This is why ketchup barely flows when you invert the bottle, until you start banging on it and it gets moving and it all comes out at once (thinned by the shear stress of your banging and gravity)