If you’ve read the Dr. Seuss book, Bartholomew and the Oobleck, and are 5 years old, like my son, you will be happy to know that this homemade oobleck is not as terrifying as the substance originating from Dr. Seuss’s imagination. In Bartholomew’s story, oobleck is a sticky green goo that falls from the sky and is impossible to remove (except through the power of a sincere apology, of course). While not magical, this homemade oobleck is even more amazing.
Going by many other names (magic mud, gloop, ooze, goop) this mixture of cornstarch and water is thoroughly mystifying and endlessly entertaining. My 3 year old and I could seriously play with this stuff for hours. My 5 year old was a little more hesitant to touch it after reading Dr. Seuss’s cautionary tale, but he eventually caved and enjoyed himself as well (which was actually nothing short of a miracle given how little this kid enjoys getting his hands dirty).
What makes oobleck so amazing? It’s a little hard to explain. You’re really going to have to make it yourself to get the full effect, but try to imagine this. You have a substance that is a liquid. It runs through your fingers. You can pour it from one container to another. Items placed on the surface sink quickly to the bottom.
Except…it’s not exactly a liquid. If you grab it, you can pick up a solid chunk (until moments later when it oozes out of your hand). If you smack it, it turns completely rigid at the moment of impact (though your kids will still prepare for the splash). If you punch it, your hand bounces off the surface. If you place your hand in it, then try to pull it out quickly, you’re stuck. I imagine this is why someone thought to name this enjoyable substance in honor of Dr. Seuss’s oobleck.
My kids and I discovered another cool feature while playing with oobleck. When my daughter tipped her pie tin full of oobleck, a big puddle poured out all over the counter. I quickly ran to grab a roll of paper towels to sop it up, but then I remembered oobleck’s ability to behave like a solid. She and I were able to grab handfuls of the puddle and stick it back in her pie tin, leaving the counter completely clean.
So, what is it? A solid? A liquid? I don’t recommend turning this fun experiment into a science lesson against anyone’s will, but if someone is curious, oobleck is a non-Newtonian fluid (so are other materials such as ketchup and quicksand) . Basically, all fluids have a property called viscosity which is a measure of the fluid’s “thickness”. For example, honey has a higher viscosity than water. For many liquids, the viscosity may be dependent on temperature (like the way honey is thicker when it’s cold), but the viscosity does not depend on pressure.
For non-Newtonian fluids, like oobleck, the viscosity is dependent on the applied pressure or shearing forces. When there are no stresses within the material, oobleck flows easily, like water. However, when external forces are applied, such as by smacking the surface or stirring it quickly, the viscosity increases dramatically. Oobleck is simply a suspension of cornstarch in water. Under ordinary circumstances, the water in the oobleck lubricates the cornstarch allowing it to flow. The best explanation I’ve found for why it behaves the way it does is that when pressure is applied quickly, the water molecules are squeezed out from between the cornstarch particles, causing the substance to become rigid.
If you’re anyone ranging from a toddler who can be trusted not to ingest random substances to a 50-something year old bachelor with grandkids (hi, Dad), I think you’ll enjoy this activity. I’m not kidding when I say that I could spend hours just running my fingers through it. It’s THAT fascinating. My kids had fun playing with their cars and toy dinosaurs in it and pretending it was quicksand.
I’ve even heard of people filling kiddie pools with it and walking on top (remember, if you walk quickly enough, you won’t sink), but that would take some serious dedication. I should point out that you don’t want too much of this stuff to go into your plumbing. We simply waited a few hours until some water had evaporated and it was completely solid, then threw ours in the trash can (though you could always save it and revive it later with a little water).
I recommend checking out Dr. Seuss’s book from the library (as nearly every library is sure to have a copy), but if you’re interested in purchasing, please consider using this Amazon affiliate link to buy Bartholomew and the Oobleck at no extra cost to you. It really is a wonderful book that teaches the lesson of appreciating what you have instead of always yearning for something more. My 5 year old loves it (even though it did make him extra wary of this activity).
Recommended Age Range: Preschool, Kindergarten
Time Required: ~5 minutes (plus endless playtime)
Cost: Less than $1 in used supplies for each child
- cornstarch (we used 2 cups per kid)
- water (we used 1 cup per kid, but you might need slightly more)
Supplies & Tools:
- bowl or pie tin
- measuring cup
- spoon (optional, can just use hands)
- food coloring (optional, could also use Kool-Aid or all natural dye)
- First place 2 cups of cornstarch in your bowl or pie tin.
- If you want your oobleck to be colored, I recommend adding the coloring to the water.
- Add 1 cup water to your cornstarch.
- Mix the water and cornstarch together. You could try to use a spoon, but I recommend using your hands.
- If needed, add a little more water. I’ve heard that some people use more, but we found 2 cups cornstarch and 1 cup water to work well. We were definitely able to get the solid properties while still having a material that flowed well.
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I haven’t read this book yet but I’ll make sure to check it out at the library. This activity looks like too much fun to miss out on it. Besides my boys love to do things like in the books or discover things they read about. I’m sure they’ll love this but I have to keep an eye on my youngest who’s still very interested in tasting everything.
My 1 year old definitely would try to eat it if I let him play too. I’m making him wait until he’s older (mostly because he would also make a giant mess), but thankfully it’s just cornstarch and water, so if he samples it, there won’t be any serious consequences.
It really is fun making oobleck! We tried mixing colours with this, and it was a good learning activity.
I’m sure my kids would love mixing colors. We had a pretty hard time keeping everything contained as it was, but maybe we’ll try again soon outside and they can mix to their hearts’ content.