Liquids and solids
From National Science Education Standards: Properties of objects and materials
Why is it so hard to get out of quicksand? Is it a solid? Is it a liquid? Can it be both? In this activity, you will make a substance that is similar to quicksand—but much more fun. Play around with it and find out how it acts differently from a normal liquid and a normal solid.
Other, more familiar substances change states (from solids to liquids to gases) when we change the temperature, such as freezing water into ice or boiling it away into steam. But this simple mixture shows how changes in pressure, instead of temperature, can change the properties of some materials.
Applying pressure to the mixture increases its viscosity (thickness). A quick tap on the surface of Oobleck will make it feel hard, because it forces the cornstarch particles together. But dip your hand slowly into the mix, and see what happens—your fingers slide in as easily as through water. Moving slowly gives the cornstarch particles time to move out of the way.
Oobleck and other pressure-dependent substances (such as Silly Putty and quicksand) are not liquids such as water or oil. They are known as non-Newtonian fluids. This substance's funny name comes from a Dr. Seuss book called Bartholomew and the Oobleck.
• 1 cup of water
• 1 to 2 cups of cornstarch
• Mixing bowl
• Food coloring (optional)
• Pour one cup of cornstarch into the mixing bowl, and dip your hands into it. Can you feel how smooth the powder is? It's made up of super-fine particles.
• Now pour the water in, mixing slowly as you go. Keep adding more water until the mixture becomes thick (and hardens when you tap on it). Add more cornstarch if it gets too runny, and more water if it becomes too thin.
• Add a few drops of food coloring if desired. (If you want to turn your Oobleck another hue, it’s easier to add the coloring to the water before you mix it with the cornstarch.)
• Oobleck is non-toxic, but please use caution when doing any science activity. Be careful not to get it in your eyes, and wash your hands after handling the Oobleck.
• Roll up your sleeves and prepare to get messy! Drop your hands quickly into the Oobleck, then slowly lower your hands into it. Notice the difference!
• Hold a handful in your open palm—what happens?
• Try squeezing it in your fist or rolling it between your hands—how does it behave differently?
• Move your fingers through the mixture slowly, then try moving them faster.
• What else can you do to test the mixture's properties?
• Extra: If you have a large plastic bin or tub, you can make a big batch of Oobleck. Multiply the quantity of each ingredient by 10 or more and mix it up. Take off your shoes and socks and try standing in the Oobleck! Can you walk across it without sinking in? Let you feet sink down and then try wiggling your toes. What happens?
Read on for observations, results and more resources.