We know about the 3 basic states of matter: liquid, gas and solid. All of them have certain properties characteristic of each group. In this activity we will talk about liquids and a property they have called viscosity. Viscosity is the resistance of a liquid to flow. When you shake water or let it run through your finger, its viscosity stays the same. Since viscosity in water does not change, we call it a Newtonian fluid. When the viscosity of a liquid changes due to the force applied to it, we called it a non-Newtonian fluid. A well-known non-Newtonian fluid is ketchup. If you turn a bottle of ketchup upside down it does not come out but if you hit the bottle, then it starts to come out. When force is applied to ketchup it reduces its viscosity allowing it to flow. In this activity we will be making another non-Newtonian fluid, but unlike ketchup, force increases its viscosity.
- 1 cup of water
- 1 bowls
- 1 spoons
- Food coloring
- 1 ½ – 2 cups of cornstarch
- Place the water in the bowl and add some food coloring, mix with a spoon.
- Add the cornstarch little by little to the water and mix.
- When it becomes a bit hard for you to mix the cornstarch and water, then your oobleck is ready!
- Dip your finger and move it gently, the oobleck will act like a liquid. Punch your oobleck, it will act like a solid.
- After you are done playing, you can save your oobleck in a resealable plastic bag.
The particles of cornstarch are suspended in the water. When you dip your finger in the oobleck and move it slowly, it allows the particles to move freely. When you apply force to the oobleck, like punching it, the cornstarch particles move closer together making it feel more like a solid.
Concepts to review:
- Newtonian fluid
- non-Newtonian fluid
- Make a big batch of oobleck, fill up an aluminum tray with it and run barefoot quickly over it. Were you able to run or did your feet sink in the oobleck?