When thinking about states of matter, water is an easy example. In its liquid form, it flows easily out of a glass. In its solid form, it makes the ice that keeps our drinks nice and cool. As a gas, it’s the steam we see rising from a pot on the stove.
But you don’t have to wait for the freezer or stove to see this transformation. Mary Sanat of Engineering for Kids RVA shows us an experiment that uses a combination of cornstarch and water (sometimes called “Oobleck”) to demonstrate changing states of matter.
How to Do It
- Put some cornstarch into a bowl or mug. (A half-cup or so works fine for a couple of little scientists to play with, but you can make more to really dig into.)
- Using about half as much water in another cup, pour it slowly into the cornstarch while stirring. (You only want to use as much water as it takes to get all the cornstarch wet, so don’t dump it all in at once.)
- You’ll know you have the right mix when you lightly tap the surface with a spoon—it will feel solid, even though you can easily stir it. (If the surface splashes like water when tapped, add some more cornstarch to get the right balance.)
- Once your Oobleck is just right, dig in! Rest your fingers on top and then reach down deep. Scoop it up with your fingers and play with it. Notice how it feels when you squeeze it tightly, or when you open your hand. It will feel like a solid one moment, and a liquid the next!
What’s Happening Here?
Mixing cornstarch and water in this proportion creates a colloid, which is just a combination of substances where one is evenly spread out through the other. This particular kind of colloid is also called a non-Newtonian fluid, because it doesn’t act like liquid as Sir Isaac Newton first described it hundreds of years ago.
When you quickly squeeze or hit this mixture of cornstarch and water, the solid particles get crowded together so it feels like a solid. When you open your hand or slowly stir it, the solid particles disperse and flow with the water, so it feels like a liquid.
You can try all kinds of things to see how the mixture will react. These kids enjoy a big vat of Oobleck by swishing their fingers through it, slapping their hands on it, even stepping on it.
To get a really fun look at how this stuff “behaves” under different conditions, you can even color it and make it dance!