Oobleck

March 14th, 2011 § 23 comments

Oobleck Goop 1Can we ever so briefly have a celebration for oobleck?  It deserves a surprise party, or at least a pat on the back, and a sweet-smelling chocolate cosmos, scabiosa pod, and hydrangea bouquet.  On days when I have scarcely been able to brush my teeth due to little grabby hands and empty bellies, I simply pour oobleck into a mixing bowl, pop in some little hands, and beam myself just about anywhere I want to be.  Keep in mind that the entire process is meant to be messy.  Prepare to clean up a bit.

This project requires the following: cornstarch, water, a bowl and small hands willing to get messy.  That’s it.  Fancy schmancy oobleck (some of you are fancy, I know) requires an eyedropper, tempera paint, and a mixing spoon in addition to the above.  The cornstarch to water ratio will most likely need some tweaking to get the ideal consistency, but 1½ cup cornstarch to 1 cup water is a good jumping off place.  Pour the cornstarch into a large mixing bowl; slowly add the water and mix.  Add smidgens of additional water with a teaspoon or eyedropper.  Ultimately, the ideal suspension will feel like molasses and will “tear” a bit when small fingers stroke its surface.

Oobleck Goop 2The viscosity of oobleck is not constant.  It behaves like a solid or a liquid depending on how much pressure is applied.  Squeeze some in your palm and it will form a solid ball.  Release the pressure and it will flow out between your fingers.  A material that behaves this way is called a “non-Newtonian liquid”—its viscosity changes depending on the stress or force applied to it.  If large force is applied (compression, agitation), it becomes viscous and stationary.  If a teeny force is applied (a gentle pour), it flows like molasses.  Why does oobleck behave the way it does?  When sitting still, the starch granules are surrounded by water.  The water’s surface tension keeps it from completely flowing out of the spaces between the starch granules.  The cushion of water provides lubrication and allows unconstrained movement of the granules.  But, if large force is applied, the water is squeezed out from between the granules and the friction between them increases considerably.  When cornstarch is heated (mmmm.  gravy, for instance), the molecular chains unravel, allowing them to collide with other starch chains to form a mesh, thickening the liquid.  Hope I have not lost you….

Oobleck Goop 3Oobleck is a “suspension,” not a solution.  Cornstarch does not dissolve in water like salt or sugar.  Instead, the tiny cornstarch particles are suspended in the water.    If you allow oobleck it to sit in a bowl for long enough, the cornstarch and water will separate.  Because of this, it is important to not wash it down the sink.  Don’t gum up those pipes!  In fact, while you were poring through your latest issue of Physical Review Letters, Volume 106, Issue 5, perhaps you came across the related article “Viscoelastic Suppression of Gravity-Driven Counterflow Instability” and then moved on to “Complex Fluids at Work.”  And then, you were super surprised hear NPR’s Weekend Edition discussion “Could Cornstarch Have Plugged BP’s Oil Well?

Maybe not.  You seriously should consider checking these out.

What is cornstarch, really?  It is obtained from the corn seed’s endosperm.  The endosperm of the seed surrounds the embryo (developing plant) and provides nutrition in the form of protein (starch) for the sprout.  Corn endosperm makes cornstarch, wheat endosperm makes flour, and barley endosperm makes, well, beer.  To see the endosperm of a corn kernel, soak a seed in water overnight and cut it lengthwise.  You will most likely be able to identify the seed coat or “pericarp,” embryo or “germ,” and the endosperm.

Corn Seed DissectionAnd the name?  The name oobleck originates from the 1949 Dr. Seuss book “Bartholomew and The Oobleck.”  In the story, the King of Didd, bored with mundane weather, asks his royal magicians to whip up something a bit more dramatic.  Soon thereafter, sticky, gummy green goo falls from the sky and wreaks havoc on his tiny village.  A fantastic story with a typical Seuss-ish moral:  There are some things in life that are best left as they are.

Something to think about.

 

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§ 23 Responses to Oobleck"

  • julia says:

    i LOVE oobleck~ my students and i had fun with it about a month ago~

  • Marcie says:

    Great, Julia! So very simple–and we could spend an entire weekend making oobleck concoctions.

  • Laura says:

    I just found your blog and love it!! Cool topics. :) I like this recipe for fun as well….bring on the mess if I can “beam myself to wherever I want to be”. ;)

    Thank you!

  • oh, glad to have found you! what a treasure of ideas. thank you.

  • kristin says:

    p.s. my own kids attend a charter public school with an agriculture theme, so when i noticed one of your favorite “loves” is workboots, i smiled.

    me too. : )

  • jojo says:

    C’est genial ton blog est magnifique a plus. Jojo.

  • […] We have a favorite recipe, and Mossy does too!  We love slimy goop! […]

  • Faiza says:

    Well I ve got a question… Suppose smb like my science teacher asks me wat oobleck really is… and i say its liquid.. wat r my justifications ??? y is it not a solid ??

    • Marcie says:

      Oobleck is considered a “non-Neutonian fluid.” This means that when a small amount of force is used on it, it acts like a liquid, and when heavy force is applied (a squeeze or punch), it acts like a solid. So, it has properties of both a solid and a liquid.

  • Faiza says:

    So if I leave oobleck in a bowl… does take the bowl’s shape ? I have made oobleck but i still do not get it :(

    • Marcie says:

      Yes, if left alone like this it will take on the bowl’s shape and act as a liquid. If poked with a spoon while in the bowl (force applied), it will act as a solid.

  • seranicia says:

    i luv it. its so fun to do:)

  • Shawn says:

    My son would like to do this for a science fair….however, the science fair is set up where they do the project at home, and share a poster board or a small demonstration at a table. I am wondering if I were to make this the night before and store it in the refrigerator, would you be able to see the different properties by simply shaking the oobleck in a glass jar? Would you be able to feel the substance get hard in the jar and then see the substance turn back to a liquid state?

    • Marcie says:

      Yes, quite sure he could keep it overnight and then bring it in the following day. Most likely, the suspension will need to be stirred the next day–the cornstarch and water will separate. To get the full effect for the science fair, he would need to open the jar and provide a spoon. People visiting the display could use the spoon to apply pressure and then let it drip from the spoon into the jar. It would be difficult for people to fully grasp the concept without physically touching the oobleck with their hands or a spoon. Should be a great project–good luck!

  • Anonymous says:

    It is so fun to make! I could play with it all day.

  • […] Messy, fun, GOOP! Mossy Mossy has the dirt on how to make slimy fun […]

  • Susan says:

    I work for a children’s theatre company and I’m just finishing up a study guide to go with our production of Seussical Jr. I’ve included information and activities to go along with some of Dr. Seuss’ books and wondered if you would mind if I include one of the photos, your recipe, and a small summary of your explanation for Oobleck. I’ll put a link to your website at the bottom of the page.

    The guide will just be sent out to teachers bringing their students to our show next week. I’m on a deadline here and need to finish this up today and get it out tomorrow, so unless I hear otherwise, will include it as described above.

    Nice website, by the way! Susan Heaton

  • Jacob says:

    Oobleck is a stubborn liquid solid.

  • anais says:

    science fair yaah oooh taaaaa daa!!!

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