RAPID CITY, S.D. (KOTA) – Each week, we bring you a quick and easy experiment you can do at home to explore a concept in science. This week, we’re exploring rheology by making oobleck. It’s a fun material that has properties of both solids and liquids – depending on the force applied to it.
If you’re using gloves, put them on at the start of the experiment.
Measure the water into the container. These instructions will assume you are using one cup of water.
If you are using food coloring, mix it into the water now. Though you can add it later in the experiment, it will be easiest to incorporate now.
Add about 1/4 of the cornstarch (half a cup if using one cup of water) and mix it into the water. Your hands will work best, though you can use a spoon or whisk if you want. As you continue to add cornstarch, mixing it will become more difficult. You may find it easiest to mix by hand.
Add another 1/4 of the cornstarch and mix again. Repeat with another 1/4 of the cornstarch.
The mixture will be getting more difficult to mix, and may already exhibit properties of oobleck. It may feel like solid around your hand while you mix it, but will loosen up if you stop moving it.
If you are finding it difficult to mix, add the final 1/4 of the cornstarch in smaller batches.
Be patient as you mix! It can take several minutes of mixing for the cornstarch to fully incorporate into the water.
Once mixed, it’s ready to play with. Keep in mind, oobleck isn’t like play-dough. It will act as a liquid if there isn’t force on it. If you slowly place your hand in the oobleck, it will feel like a liquid – but if you try and remove your hand quickly, you will feel a lot of resistance as it becomes more solid.
You can also try squeezing some oobleck into a ball in your hand, then watching it drip out when you stop squeezing.
When you’re ready to dispose of your oobleck, put it in the garbage and not down your drain. Although oobleck looks like a liquid, it can cause clogs.
Oobleck is a non-Newtonian fluid. This means that the viscosity, or thickness, of oobleck depends on the force applied to it.
The more force you apply to oobleck, the thicker it becomes. This is because the cornstarch particles are suspended in the water – each separated by a small amount of water. When force is applied, the water between these particles is forced out and temporary clumps of solid cornstarch form.
This type of non-Newtonian fluid is known as a shear-thickening fluid. The more force that gets applied, the thicker it becomes.
There are other non-Newtonian fluids, which oobleck can be a good way to discuss. Several biological fluids are shear-thinning non-Newtonian fluids. This means that they get thinner when force is applied.
Ketchup is an example – when you shake a ketchup bottle, you’re actually making it thinner and easier to squeeze.
Another example is our blood, which changes its thickness in order to circulate more efficiently depending on the size of the vein.
The study of the flow of matter is called rheology. It’s a fascinating branch of science!
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