What Happens When You Mix Cornstarch With Water? Exploring Non-Newtonian Fluid Dynamics
The result of mixing cornstarch with water is the creation of a fascinating and counterintuitive substance known as oobleck: a non-Newtonian fluid that behaves as both a liquid and a solid, depending on the applied force.
Unveiling Oobleck: A Deeper Dive
The seemingly simple mixture of cornstarch and water gives rise to a substance with bizarre properties, captivating scientists and children alike. Oobleck’s unique behavior stems from its status as a non-Newtonian fluid. Unlike water, which flows consistently regardless of the force applied, oobleck’s viscosity (its resistance to flow) changes dramatically. Understanding this behavior requires delving into the microscopic interactions between cornstarch particles.
What Makes Oobleck a Non-Newtonian Fluid?
Newtonian fluids, like water, follow a predictable relationship between stress and strain. Apply pressure, and they flow predictably. Non-Newtonian fluids, however, defy this simplicity. Their viscosity changes under stress. Oobleck specifically exhibits a phenomenon called shear thickening.
- Shear Thickening: When pressure or force (shear stress) is applied, the cornstarch particles compress together, increasing the viscosity and making the mixture feel solid.
- Shear Thinning: When little or no pressure is applied, the cornstarch particles can slide past each other more easily, decreasing the viscosity and making the mixture flow like a liquid.
This strange behavior arises because cornstarch particles are irregular in shape and size. At rest, they are surrounded by a layer of water molecules, allowing them to slide past each other relatively freely. However, when force is applied, the water layer is disrupted, and the irregular particles collide and jam together, forming a temporary network that resists deformation.
The Recipe for Oobleck: Ratios and Preparation
Creating oobleck at home is a fun and educational experiment. Here’s a basic recipe:
- Ingredients:
- Cornstarch (approximately 1 cup)
- Water (approximately 1/2 cup)
- Optional: Food coloring
- Instructions:
- Pour the cornstarch into a bowl.
- Slowly add the water, mixing with your hands or a spoon.
- Continue adding water until the mixture reaches the desired consistency – it should feel solid when you apply pressure but flow when you let it rest.
- Add a few drops of food coloring if desired, and mix thoroughly.
The exact ratio of cornstarch to water can vary slightly depending on the cornstarch and the humidity. Start with the suggested amounts and adjust as needed until you achieve the desired consistency.
Demonstrating Oobleck’s Unique Properties
Here are a few ways to showcase the remarkable characteristics of oobleck:
- The Punch Test: Quickly punch the surface of oobleck. It should feel solid momentarily.
- The Walking on Water Illusion: If you create a large enough batch in a sturdy container, you can briefly walk on the surface of the oobleck if you move quickly.
- The Squeeze and Release: Squeeze a handful of oobleck tightly in your hand, and it will feel solid. Open your hand, and it will flow through your fingers like a liquid.
- Vibration Test: Place oobleck on a speaker and play a low-frequency tone. The vibrations will cause the oobleck to form interesting shapes and patterns.
Applications Beyond the Classroom: Potential Uses of Shear-Thickening Fluids
While often used for educational demonstrations, shear-thickening fluids like oobleck have potential applications in various fields:
- Body Armor: Researchers are exploring the use of shear-thickening fluids in body armor. These fluids can provide impact resistance, potentially offering a lighter and more flexible alternative to traditional armor.
- Automotive Safety: Shear-thickening fluids could be used in car bumpers to absorb impact energy and reduce damage during collisions.
- Road Construction: Certain formulations of shear-thickening fluids can be used as additives to improve the durability and load-bearing capacity of roads.
Common Mistakes and Troubleshooting
Creating oobleck is generally straightforward, but here are some common pitfalls to avoid:
- Adding too much water: This will result in a watery mixture that doesn’t exhibit the desired shear-thickening properties. Add more cornstarch to compensate.
- Adding the water too quickly: Adding all the water at once can make it difficult to mix properly and create lumps. Add the water slowly and gradually.
- Using the wrong type of cornstarch: Ensure you are using pure cornstarch and not a cornstarch substitute or a product with added ingredients.
- Getting discouraged: It may take a few attempts to get the consistency just right. Don’t give up!
Cleaning Up Oobleck: A Simple Process
Cleaning up oobleck is surprisingly easy. Simply let it dry completely, and it will turn into a powder that can be swept or vacuumed up. Avoid pouring oobleck down the drain, as it can clog pipes.
Frequently Asked Questions (FAQs) About Cornstarch and Water Mixtures
What exactly is viscosity, and how does it relate to oobleck?
Viscosity is a measure of a fluid’s resistance to flow. A fluid with high viscosity, like honey, flows slowly, while a fluid with low viscosity, like water, flows easily. Oobleck’s unique characteristic is its variable viscosity; it changes depending on the force applied, demonstrating a non-Newtonian behavior that distinguishes it from fluids with constant viscosity.
Is oobleck dangerous to touch or handle?
No, oobleck is generally considered safe to touch and handle. Cornstarch is a common food ingredient and is not toxic. However, it is important to avoid ingesting large quantities of oobleck, as it could cause digestive discomfort. Also, avoid getting oobleck in your eyes.
Can I store oobleck for later use?
Yes, oobleck can be stored for later use. Place it in an airtight container to prevent it from drying out. If it does dry out, simply add a little water to restore its original consistency. Stored oobleck might require stirring to redistribute the water evenly before each use.
What other substances exhibit similar non-Newtonian fluid behavior?
Oobleck is just one example of a shear-thickening non-Newtonian fluid. Other examples include:
- Silly Putty
- Quicksand
- Some types of paint
- Certain drilling muds used in the oil industry
Why is oobleck used in educational settings?
Oobleck is a fantastic teaching tool because it provides a tangible and engaging way to introduce concepts related to physics, chemistry, and material science. It helps students understand the properties of fluids, the behavior of matter under stress, and the difference between Newtonian and non-Newtonian fluids.
Can I add other ingredients to oobleck to change its properties?
Yes, you can experiment with adding other ingredients to oobleck. For example, adding sand or beads can change its texture and flow properties. However, be aware that adding certain substances might alter the oobleck’s non-Newtonian behavior or make it more difficult to clean up.
Is oobleck the same thing as slime?
No, oobleck and slime are different substances with distinct properties. Oobleck is a suspension of cornstarch particles in water and exhibits shear-thickening behavior. Slime, on the other hand, is typically made from polymer solutions, such as glue or borax, and often exhibits viscoelastic properties.
Does temperature affect the properties of oobleck?
Temperature can have a slight effect on the properties of oobleck. Warmer temperatures may make the mixture slightly more fluid, while colder temperatures may make it slightly more viscous. However, the primary factor affecting oobleck’s behavior is the applied force, not the temperature.
What is the science behind walking on oobleck?
Walking on oobleck is possible because of its shear-thickening behavior. When you quickly step onto the oobleck, the force applied causes the cornstarch particles to jam together, creating a temporary solid surface that can support your weight. However, if you stand still, the pressure decreases, and the oobleck reverts to its liquid state, causing you to sink.
How does oobleck compare to quicksand?
While both oobleck and quicksand are non-Newtonian fluids, they behave differently. Oobleck is shear-thickening, becoming more solid under pressure. Quicksand, on the other hand, is shear-thinning; it becomes less viscous when disturbed, which is why people sink in it.
Are there any safety precautions I should take when making or using oobleck?
While oobleck is generally safe, it’s important to take a few precautions. Avoid pouring oobleck down the drain, as it can clog pipes. Supervise children when they are playing with oobleck to prevent them from ingesting large quantities. And always wash your hands after handling oobleck.
What happens if I try to mix oobleck in a washing machine?
Mixing oobleck in a washing machine is generally not recommended. The force and agitation of the washing machine could damage the machine, and the oobleck could clog the drain. It is best to create and experiment with oobleck in smaller, more controlled environments.