It's a Solid... It's a Liquid... It's oobleck!

Key concepts :

Liquids and solids

Viscosity

Pressure

Materials

• 1 cup of water

• 1 to 2 cups of cornstarch

• Mixing bowl

Preparation

• 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.

Procedure

• 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?

Read on for observations, results and more resources.

Observations and results

What is happening when you squeeze the Oobleck? What is happening when you release the pressure?

Applying pressure to the mixture (oobleck)  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 when you dip your hand slowly into the mix, and see what happens—your fingers slide in as easily as thoroughly (like liquid). Moving slowly gives the cornstarch particles time to move out of the way. The Oobleck mixture isn't your typical liquid—or solid. The cornstarch-and-water mixture creates a fluid that acts more like quicksand than water: applying force (squeezing or tapping it) causes it to become thicker. If you were trapped in a tub of Oobleck, what would be the best way to escape?