Goop, also called oobleck, was a new experience for us. It was inexpensive, easy to make, very mess, and a whole lot of fun!
We set up on the kitchen floor; you really don't want to do this in a carpeted area. I found an empty plastic bin and dumped a whole box of cornstarch in it. I let the girls feel the cornstarch to see how soft it was. Then we started adding our water. Mix it up as you're adding water. We just used our hands for mixing. Add the water until it's a soft liquid, about the consistency of honey.
Now it's time for fun. Squish it quickly with your hands; it feels solid and crumbly. Run your hands slowly through it; now it feels liquid. Grab a handful and squish it like a ball. Now, open your hands and watch it flow slowly out. Goop is an interesting mixture that is both a solid and a liquid.
After playing for awhile, we added a bunch of old kitchen tools from our sandbox. We had whisks, scoops, and measuring spoons. Try whisking quickly. It's hard to do! They loved the sensory experience and spent a lot of time pouring it on their arms. The goop did make a massive mess. But, it does clean up easily. I was able to sweep it off my kitchen floor once it had dried. Also, it came off their clothes with a simple washing.
The Science Behind Goop
The mixture of cornstarch and water is a suspension. The two substances combine, but will eventually separate again. Another example of a suspension is muddy water. The viscosity, or thickness and resistance of flow, of this mixture reacts to force. So, when you quickly grab a handful, the cornstarch particles temporarily trap the water particles. When you release, the mixture turns to liquid again. You can read this post at Steve Spangler Science about cornstarch science for a more detailed explanation.
Have you ever made goop? It's a fun science and sensory experience.