week 4: solid or liquid?

​Oobleck is a well-known guest at the party when it comes to science projects. It's very easy to make, and even easier to play with. However, many people don't know what makes oobleck the way it is -- and what it means to be a non-Newtonian fluid.

Materials: 

• 2 cups cornstarch
  
• 1 cup water
  
• bowl
  
• spoon
  

Directions:

1. Mix the cornstarch and water in the bowl.
   
2. Stir with a spoon until the mixture has the consistency of pancake batter.
   
3. Observe the mixture. Try to poke it with your finger, scoop some of it up, or roll it into a ball. What happens if you leave the ball in your hand for a couple of seconds? How about a couple of minutes?
   

What's Going On?
Oobleck is not a solid or a liquid. It is a special substance called a "non-Newtonian fluid." Non-Newtonian fluids are pressure-dependent. This means that adding more pressure to these fluids can change their thickness, or viscosity. As you observed, shaping the Oobleck into a ball required some pressure by your hands, which in turn increased the viscosity of the fluid. On the other hand, when there was little pressure on the Oobleck, such as when it was simply on your palm, it becomes less viscous and thus is less rigid. Other non-Newtonian fluids include quicksand, magma, and even your own blood! Newtonian fluids (which are liquids such as water) are the opposite of non-Newtonian fluids.