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By Mom Unplugged, November 10, 2008 10:00 pm

Today, along with a visiting friend, we finally got to do this week’s kitchen Unplugged Project. We used cornstarch, a common kitchen ingredient, to create a non-Newtonian fluid. The other name for such a mixture is Oobleck, from the Dr. Seuss book, Bartholomew and the Oobleck.

It was SO COOL!! The kids and I found it fascinating! I was so enthralled that I felt that the mess (and there WAS mess), was actually very worthwhile.

I set out four small mixing bowls and spoons, one for each child. I also set out water, cornstarch, and measuring cups.

The kids each put about one cup of cornstarch into their bowl.

I had them add water just a bit at a time,

and stir until we got the “right” consistency.

It was probably close to about a half to two thirds of a cup of water, but the “right” consistency was quite obvious. When the mixture starts to feel hard to stir although it looks like liquid on the top, then it is probably about ready.

Test it by dipping your hand in, lifting out some fluid, and squeezing it into a ball. It should feel like a hard, dry ball in your hand but when you open your fingers, it will turn back into a liquid and run back into the bowl.

Here is a fleeting picture of it as a solid:

Adjust your mixture by adding a bit of water if too dry, or a bit of cornstarch if too wet. You’ll know you have it right when the oohs and aahs begin!

This was so much fun to play with and was a very weird sensation that is quite hard to describe. The children (including my 2 year-old) and I played for maybe an hour: squeezing, stirring, punching, and even hammering!

My favorite trick: If you roll it between your two palms as if you are making a ball with clay, it makes a nice solid ball, but as soon as you release the pressure, it all runs away!

Also, put a finger gently into it and it will slowly and strangely be sucked under as if in quicksand. Jab the finger in quickly, and it will hit a hard surface.

The Science:

As I understand it, when you squeeze the mixture, or compress it quickly in some way (hammer, punching, etc.), the molecules compress and become a solid. When the pressure is released, the molecules spread out again and the mixture becomes a liquid. As my oldest daughter said: “Oooo! I can feel it changing from a solid to a liquid!”

Here are two good explanations of what a non-Newtonian fluid is:

“Oobleck is often referred to as a ‘non-Newtonian’ substance because it does not behave as Newton’s Third Law of Motion states; for every action, there is an equal and opposite reaction. Applying this principle, you would expect Oobleck to ‘splash’ when you ‘smack’ it with your hand. (Smacking is the action, splashing is the reaction.) However, when you try this out Oobleck does not splash, in fact, it becomes a solid substance for a few moments.”

(from Oobleck - a Non-Newtonian Fluid)

or

“Isaac Newton defined normal liquids as having consistent flow behavior affected only by temperature or pressure; so fluids that change their resistance to flow (viscosity) under stress are not ‘normal’. Some of these fluids get runnier when stress is applied, like paint, toothpaste and slug mucus. Some get thicker, like quicksand and Oobleck.”

(from Science in the City - Bullet Proof Goo)

As to why it behaves this way, it seems that this is actually a matter of some controversy, but here are some links that are more knowledgeable than I:

Oobleck - a Non-Newtonian Fluid

More About Liquids: Thick and Thin

Fun:

You can actually walk on this stuff! My son wanted to try it after seeing this You Tube video.

(There are a few other walking on cornstarch videos out there if you are really into this!)

Tips:

1) I STRONGLY recommend that you either do this outside in an area that you can just hose off afterwards, or use a vinyl tablecloth that you can remove and hose off afterwards. Why didn’t I use mine?

2) Be sure to add the water a bit at a time, it is easy to overdo it.

3) If you do forget the tablecloth like I did, you will find that non-Newtonian fluids can be difficult to clean off a table. When you try wiping what looks like liquid, it turns into a solid and sticks.

When you stop scrubbing it returns to a liquid state! After a bit of frustration I used my science brain and poured water on the table. I was able to wipe the now runny cornstarch liquid into a trash can.

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Although I suggested it humorously yesterday, I have actually had several votes for an Unplugged Project theme next week involving “sort, trash, junk, donate.” Well, why not??

As Captain Jean-Luc Picard would have said (see, I haven’t always been without a TV!): “Make it so.”

Let’s call next week’s theme:

Sort-Junk-Donate

Remember, the theme can be loosely interpreted if you don’t feel like cleaning your house this week. Just be creative and have fun!