COSI Quicksand

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1. Cover your work area with newspaper.

2. Place the pie pan in the center of the table. Using the dry measuring cups, measure 1½ cups of cornstarch and place it in the pie pan.

3. Using the liquid measuring cup, measure 3/4 cup of water and add this to the cornstarch.

4. Stir until the mixture is smooth (this will take some time).

5. Add more water or cornstarch until you get a mixture that "cracks" when you quickly scrape your finger through it and then "melts back together again."

Now, explore! Rub a very small amount of the COSI Quicksand between your fingers. How does it feel? Gently pull your fingers through the COSI Quicksand. What do you observe? Scoop up some of the COSI Quicksand. Can you roll it into a ball? Does the ball keep its shape? Can you stretch it? Will it ooze between your fingers? Place a metal paper clip or other small, flat object on the mixture. What happens? What happens if you punch your hand into the COSI Quicksand in the pan?

COSI Quicksand is a suspension (a liquid containing small solid particles that easily separate out of the mixture) of cornstarch in water. This substance has, under varying conditions, the properties of both a liquid and a solid. It is called a non-Newtonian fluid, which means that it sometimes doesn’t behave like a liquid should according to Newton’s Laws. Upon impact, most liquids splatter and splash. In a non-Newtonian liquid, the physical structure of the material changes, increasing the thickness of the solution, making it behave more like a solid. Why? Good question.

Scientists don’t know exactly why non-Newtonian liquids behave the way they do. There are many theories. One theory suggests that water can’t easily get between the cornstarch particles when there is a sudden pressure or movement. This makes it harder for the cornstarch particles to slip against each other, and so the COSI Quicksand behaves like a solid. There are other theories as well. Perhaps you will be the scientist who solves the puzzle of non-Newtonian liquids some day!

Real quicksand is another suspension, of sand and water, and another example of a non-Newtonian substance. If you are stuck in quicksand, the best way to get out is to slowly turn so you are lying on your back, and then slowly lift your legs up to the surface. Then quickly roll across the top of the quicksand to escape. What would be the best way to pull someone out of quicksand? (Slowly, because the more stress you put on the quicksand, the thicker the mixture becomes).