Ooooooo blech: the recognition that something is both astoundingly cool and disgustingly yucky. Now I know why school children call this cornstarch/water mixture Oobleck.
Since I don’t have children in school, the first time I encountered Oobleck was at San Francisco’s mega hands-on science museum, the Exploratorium. An exhibit had this liquid (or is it a solid?) in a giant drum. Press a button, and the drum shook rapidly. The Oobleck turned into a solid until the shaking stopped. I had to try this magic at home.
Fortunately Cooper’s Mind Blowing Science Kit had the recipe: 1/8th cup water and 5 T. cornstarch. Mix it up and enjoy the magic. During stirring, Oobleck becomes solid at the bottom of the bowl and difficult to move. But, if you stop stirring and gently touch the top, it feels like a liquid. The process of hardening under pressure or intense shaking is the opposite of the liquefaction that occurs during earthquakes.
Oobleck is a non-Newtonian fluid, also called a shear-thickening liquid, but it’s not the onlyone. Gravy thickens when you stir it (or so you hope). Struggle in quicksand, and it will be more difficult to escape. These substances defy Newton’s principle that applying pressure twice as hard to a liquid should move the liquid twice as fast. Good luck if you try that with Oobleck. Here’s a great explanation of Newton’s theories.
Mix up these common household ingredients, and check it out. I have to admit, I had even more fun than the kids.
Kirsten W. Larson 
This is so incredibly cool! I love learning stuff like this. Thank you!
You are welcome!