WHAT’S GOING ON?
“Oobleck” is the popular name given to a corn starch and water mixture. This mixture has the fascinating property of being a solid or a liquid depending on the pressure, or shearing force, exerted upon it. More on this down below, but in practical terms, it means that smacking the Oobleck Pool with your feet temporarily turns the surface into solid. But if you place you feet (or hands, or elbow etc) into the Oobleck slowly, you’ll get sucked right in.
WHERE DOES THE NAME “OOBLECK” COME FROM?
The term “Oobleck” comes from an early work of Dr. Seuss, Bartholomew and the Oobleck. Magicians make a green gooey substance come down from the sky; it creates havoc in the land and look quite similar to the cornstarch and water mixture when you play with small amounts of it and let it drip. Our Oobleck can create havoc too - if you get stuck in it!
WHAT IS A NON-NEWTONIAN FLUID?
This might be best answered by defining a “Newtonian” fluid, which is an ideal liquid. In lay terms, the flow of a Newtonian fluid will not change no matter what you do (assuming constant temperature). If you consider water, you can pour water our slowly, or stir it really fast, or shake it up in a bottle and flows remains the same in all conditions. The viscosity does not change.
In contrast, consider trying to get ketchup out of a glass bottle. The ketchup will sit, clumped, requiring you to bang the bottle to get it out . . . at which point it would all come out at once. The applied force (hitting the bottle) causes the viscosity of the ketchup to change. The Oobleck is a mixture of corn starch and water. When you apply force to this mixture, the mixture hardens, enough so that you can walk on a pool of it. But if the force is too weak, the substance will act as a liquid and you will sink right in.