Key concepts
Liquids and solids
Viscosity
Pressure

From National Science Education Standards: Properties of objects and materials

Introduction
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.

Background
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.

Materials
•    1 cup of water
•    1 to 2 cups of cornstarch
•    Mixing bowl
•    Food coloring (optional)

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?
•    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.

4 Comments

1. 1. SigmaEyes 05:50 PM 5/4/11

   This is cool, even for an adult woman without children handy! I mixed some up just for fun. But seeing how solid it could be, I was afraid to dilute it down the drain. So I poured it out onto a big sheet of aluminum foil, and set it out in the garage to evaporate. After a few days, in the trash it went. Makes me want some silly putty again -lol

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2. 2. karen00100 06:10 PM 5/5/11

   This is a cool activity. I did this about 6 weeks ago in response to a question my 10 yr. old grandson about quicksand. I remembered doing this as a kid,but withouth the scientific info to go along with it.
   
   Years later in a chemistry class it all 'coalesced' (pun intended) for me when we were talking about solids, liquids and gasses.
   
   I always have fun with it when I am using cornstarch to thicken anything I am cooking. Even old grandmas play with their food sometimes.
   
   Thanks and keep the activities coming.

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3. 3. kengleka 08:40 AM 5/7/11

   This is a great activity but I think there is a teaching opportunity missing. Cornstarch molecules are long and stringy, like spaghetti. A bowl of spaghetti noodles acts just like this substance - punch it and your fist is stopped, but push your fist into it slowly and the noodles have time to move out of the way and your fist penetrates the surface. Even very young children seem to understand this example and it gives them a peek into the idea that the shape of molecules has something to do with the way they behave.

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4. 4. juliadumars 01:00 AM 6/7/11

   We have done this many times for fun at home, but never built in the lesson about changing the state of matter through change in pressure as opposed to temperature. I like the point about the shape of cornstarch molecules too. I will post a video of my 8 yr old mixing up some oobleck on the Scientific American FB page

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