Do you know how to make oobleck or even what, exactly, it is? Oobleck is the name of a non-Newtonian fluid made by mixing corn starch and water. It has the name “oobleck” because it resembles the green stuff called oobleck in the Dr. Seuss book, “Bartholomew and the Oobleck.”
In the story, the King wants a replacement for rain and snow. The Royal Magicians produce oobleck, a green gelatinous substance that entraps objects and people. Bartholomew saves the day by getting the King to take back his wish, returning the weather to normal.
The oobleck you make is not exactly magical, but it does display interesting properties. Here is how to make it and a look at how it works.
Non-Newtonian Fluids
A non-Newtonian fluid is one that experiences viscosity changes, depending on mechanical conditions. In other words, sometimes it flows like a liquid and other times it does not flow, like a solid. In contrast, a Newtonian fluid maintains pretty much the same viscosity, no matter what you do to it.
There are different types of non-Newtonian fluids. For example, slime is a non-Newtonian fluid that flows under low stress, but breaks under pressure. Ketchup is a non-Newtonian fluid that is a shear-thinning fluid. It does not easily flow, but if you tap or shake a ketchup bottle, its contents suddenly change to a lower viscosity and pour out.
Oobleck is a type of non-Newtonian fluid called a dilatant. A dilatant is a shear-thickening fluid (the opposite of ketchup). Applying shear stress by punching or squeezing instantly thickens oobleck, so it acts like a solid. Releasing stress lets oobleck flow, like a liquid. For example, oobleck supports your weight if you run across a layer of it. But, you sink into it if you walk slowly.
How to Make Oobleck
Oobleck is simple to make, inexpensive, non-toxic, and uses familiar ingredients:
- 1½ -2 cups corn starch
- 1 cup water
- food coloring (optional)
- Make any amount of oobleck using 1.5 to 2 parts corn starch to 1 part water. For example, mix together 2 cups of corn starch and 1 cup of water.
- Add food coloring, if desired. The color of oobleck in the Dr. Seuss story is green.
Unlike slime, oobleck is not sticky. All you need for clean-up is water, unless you use food coloring. Re-use the oobleck as much as you like. When it dries out, just add a bit more water. If it’s too wet, add more corn starch.
Fun Oobleck Activities
Explore the interesting properties of oobleck:
- Play with a bowl of oobleck. Watch it ooze through your fingers. Squeeze it and feel how it changes consistency.
- Draw shapes in the oobleck. How long do they last? Does it matter how quickly you draw?
- Pour a large batch in a metal or plastic bin. Walk through it. See how long it holds you up if you stomp on it.
- Seal oobleck in a zip-top plastic bag. Compare what happens when you slowly squeeze it to its behavior when you shake it or drop it.
- Place a dish of oobleck on top of a subwoofer. Play low frequency sounds at high volume and see the forms the oobleck takes.
How Oobleck Works
Oobleck acts the way it does because of the way corn starch and water mix together. They form a colloidal mixture, with large starch grains surrounded by water. At rest, the high surface tension of water forms lubricating droplets around the granules of corn starch. The cushion of water permits flow. Compressing the mixture forces the starch together and locks them in position. So, under shear stress, oobleck behaves more like a crystal.
References
- Chhabra, R.P. (2006). Bubbles, Drops, and Particles in Non-Newtonian Fluids (2nd ed.). Hoboken: Taylor & Francis Ltd. ISBN 978-1420015386.
- Dr. Seuss (1949). Bartholomew and the Oobleck. Random House Books for Young Readers. ISBN: 978-0394900759.
- Rupp, Rebecca (1998). “Magic Mud and Other Great Experiments”. The Complete Home Learning Source Book. ISBN 9780609801093.
- Tropea, Cameron; Yarin, Alexander L.; Foss, John F. (2007). Springer Handbook of Experimental Fluid Mechanics. Springer. ISBN 978-3-540-25141-5.