Cornstarch & Water

Today’s awesomeness I hope you have seen before – mixing cornstarch and water.  In college, I worked at a before and after school program for kindergarten through fifth graders.  Cornstarch and water {or oobleck as we called it} was a favorite for all ages.  Of course, I had to share the joy of oobleck with my son {he’s 2}.

Food coloring (optional but way cooler with)
Spoons for stirring

Optional tools for added fun {and learning}:

  • measuring cups
  • cookie cutters
  • bowls
  • etc!

I covered my table with plastic (a cheap plastic drop cloth I reuse for painting and messy things).  I placed a large piece of freezer paper on the table as well.  {You’ll notice Aiden is wearing a shirt covered in paint – that’s not from this activity…we painted before we played with the cornstarch and water.}

{You really could just have your kids experiment with the cornstarch and water and let them figure out how make oobleck.  Here are some tips just in case.}

  1. Add some cornstarch to a bowl {or directly to your work station} – maybe a 1/2 cup or a cup — I really didn’t measure this time {totally scientific right…hehe}.
  2. Add a little bit of water – only a tablespoon or two at a time.  {I let Aiden be in charge of this, and he dumped the entire bowl of water into the cornstarch.  We started over because that was going to require way too much cornstarch to make it work well.
  3. Stir with a spoon {or use your hands}.  Allow your kids to experience how the mixture behaves with just a little bit of water.  I can only describe it as a squishy solid…
  4. Slowly add more water until you get a nice goopy texture.  When you move through the mixture slowly, it will feel like slimy liquid.  If you just tap hard on the mixture, it will act like a solid.  This is what makes it sooo fun!  Pick it up, bounce it around in your had, treat it like play dough, then let it ooze down.
  5. Add food coloring when ever you want.  {You’ll probably have dyed hands, but it will eventually wear off.}
After getting the consistency I wanted, I dumped the mixture onto the freezer paper and stirred in some food coloring.  I let Aiden have at it.  He loved to pick it up and just let it drip from his hands.
The Science Behind It
Oobleck is a non-Newtonian fluid.  It doesn’t behave like a “normal” liquid.  It has properties of both a solid and a liquid depending on the amount of stress applied.  When stress is applied, the cornstarch and water mixture acts like a solid {your hand can’t go through; you just squish it like play dough}.  When constant stress is not applied, the mixture acts like a liquid.
Other examples of non-Newtonian fluids like the cornstarch and water mixture are mud and wet sand.  It is easier to travel across mud or wet sand when you run.  You will stay on top.  If you walk slowly, you will sink!
Ketchup and toothpaste are also non-Newtonian fluids except they behave in the exact opposite way of oobleck.  When stress is applied they are thinner {rather than thicker like oobleck}.

Questions for Learning

  • What happens when you add water to the cornstarch?
  • What happens if you add too much water?
  • Describe the texture of the mixture.
  • What makes the oobleck act like a solid?
  • When does it act like a liquid?
  • What do you think would happen if we let the oobleck sit for a while?  {It will eventually dry out and turn back into powdery – all be it colored – cornstarch.  Try it!}
I hope you play with cornstarch and water {again} soon!
Thanks for reading!

It's Playtime at hands on : as we grow

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