Non-Newtonian Fluids (Oobleck)

Non-Newtonian Fluids (Oobleck)

Cornstarch-water mixtures acting as solids/liquids.

Dive In: Is It a Liquid or a Solid? It's Oobleck!

Imagine a substance that feels like a liquid when you gently pour it, but instantly turns hard like a solid if you hit it or squeeze it quickly! Then, as soon as you stop, it melts back into a gooey liquid. Sounds like something out of a science fiction movie, right? Well, you can make this amazing material, often called Oobleck, right in your own kitchen using just cornstarch and water! Oobleck is a fantastic example of a non-Newtonian fluid, which behaves in weird and wonderful ways. Understanding these fluids helps engineers design better materials for things like shock absorbers, bulletproof vests, and even specialized paints.

The Science Scoop: Flowing When Slow, Freezing When Fast

Most liquids you encounter every day, like water or oil, are Newtonian fluids. This means their "thickness" or viscosity (how easily they flow) stays the same no matter how much force you apply to them. Water always pours like water.

But Oobleck is different. It's a non-Newtonian fluid, specifically a shear-thickening fluid. This means its viscosity changes depending on the amount of stress or "shear" (force) you apply to it.

Here's how it works:

1. Cornstarch Particles: Cornstarch is made of incredibly tiny, solid particles. When you mix them with water, they don't dissolve. Instead, they remain suspended in the water.

2. Water as a Lubricant: The water acts as a lubricant, allowing the cornstarch particles to slide past each other easily when you apply slow, gentle pressure. This makes Oobleck feel like a liquid.

3. The "Jamming" Effect (Shear Thickening): When you apply sudden, strong force (like hitting it, squeezing it quickly, or stomping on it):

   • The water doesn't have time to move out of the way.

   • The cornstarch particles are forced closer together, quickly losing their water lubrication.

   • They "jam" or "interlock" very rapidly, briefly forming a rigid, solid-like structure.

   • This creates a sudden increase in the mixture's viscosity, making it feel hard.

4. Returning to Liquid: As soon as the force is removed, the cornstarch particles are no longer jammed, and the water can once again act as a lubricant, allowing the mixture to flow like a liquid again.

This unique behavior is what makes Oobleck so fascinating and fun to play with. It demonstrates that the traditional categories of "solid" and "liquid" aren't always so clear-cut, especially when you consider materials at the particle level and how they respond to different forces.

For Educators: Teaching Tips

• Hands-on, Messy Fun: This is the ultimate hands-on experiment. Be prepared for a bit of mess!

• Predict and Observe: Have students predict what Oobleck will do before they interact with it.

• Vocabulary: Introduce "non-Newtonian fluid," "viscosity," "shear-thickening," and "particles."

• Compare and Contrast: Directly compare Oobleck's behavior to water (Newtonian) and playdough (solid).

• Safety: Emphasize that Oobleck is not for eating (even though cornstarch is food-safe, the mixture is not intended for consumption). Dispose of it properly (not down drains!).

Experiment Time: The Oobleck Dance!

These experiments will let students directly interact with Oobleck and witness its unusual properties.

Experiment 1: Make Your Own Oobleck!

• Materials: Cornstarch, water, a mixing bowl, a spoon, a measuring cup.

• Procedure:

  1. Pour about 1 cup of cornstarch into the mixing bowl.

  2. Gradually add about 1/2 cup of water to the cornstarch, mixing with the spoon.

  3. Keep mixing and add tiny bits more water (or cornstarch) until you get a consistency that's thick but still flows slowly. It should feel solid when you push on it quickly but liquid when you let your hand sink in slowly.

• Discussion: What does it feel like? How does it look? Does it remind you of anything else?

Experiment 2: The "Punch or Pour" Test

• Materials: Your freshly made Oobleck.

• Procedure:

  1. Gently pour the Oobleck from the bowl into your hand. How does it behave?

  2. Now, try to quickly punch the surface of the Oobleck in the bowl. What happens?

  3. Try to slowly push your finger into the Oobleck. What happens?

  4. Try to quickly grab a handful of Oobleck, squeeze it tightly, and then let it go.

• Discussion: What happened when you tried to punch it? What happened when you slowly pushed your finger in? How did it feel when you squeezed it quickly in your hand? What does this tell you about how Oobleck responds to different forces?

Experiment 3: Oobleck on a Speaker (Advanced, for Observation)

• Materials: Oobleck, a large, sturdy speaker, a smart phone or computer to play low-frequency sounds (bass-heavy music or a tone generator app), plastic wrap.

• Procedure:

  1. Cover the speaker cone securely with plastic wrap to protect it.

  2. Pour a thin layer of Oobleck onto the plastic wrap covering the speaker cone.

  3. Play very low-frequency (bass) sounds. Watch what happens to the Oobleck.

• Discussion: What kind of amazing shapes does the Oobleck make when the speaker vibrates? Why do you think it behaves this way? (The rapid vibrations from the speaker cause the Oobleck to repeatedly thicken and thin, creating complex, dancing patterns and even "spikes").

Safety Note for Teachers:

• Do not eat Oobleck.

• Do not pour Oobleck down the drain. It can clog pipes! Dispose of it in the trash.

• Be prepared for mess. Use trays or tablecloths.

Learn More: Explore Further!

• For Young Learners:

  • Videos: Search YouTube for "Oobleck science for kids," "non-Newtonian fluids explained," or "cornstarch and water experiment."

  • Books: Look for children's science books on states of matter, surprising science experiments, or materials.

• For Teachers & Parents (More In-Depth): 

  • Scientific American / Physics Today: Often feature articles on non-Newtonian fluids and their applications.

  • "Non-Newtonian fluid" and "Oobleck" Wikipedia pages: Provide detailed scientific explanations.

  • General fluid mechanics textbooks: Look for sections on non-Newtonian fluids.

  • Websites on materials science and engineering: Many discuss shear-thickening fluids and their uses.

References

• Barnes, H. A., & Hutton, J. F. (1989). An Introduction to Rheology. Elsevier. (A classic textbook on rheology, the study of the flow of matter, including non-Newtonian fluids).

• Jaeger, H. M., Nagel, S. R., & Behringer, R. P. (1996). Granular Solids, Liquids, and Gases: Viewpoints of a New Field. Reviews of Modern Physics, 68(4), 1259. (While broader, this seminal paper discusses the jamming transitions relevant to shear-thickening granular materials).

• Many educational resources and kitchen science experiment guides provide practical instructions and basic explanations for making and exploring Oobleck.