Today in 3rd grade's class connect lesson, we learned about solids, liquids, and gases. No good science lesson is complete without a little experimenting...so we made OOBLECK! Oobleck is a cornstarch+water mixture that has properties of both solids and liquids. It entertained everyone at my house today...from my one year old daughter to my 19 year-old sister! I borrowed these directions from www.sciencebob.com
This may just be the easiest, messiest, and most fun science activity
I know. It is a classic, and I have gotten several requests recently to
post directions. You should know that if you try this activity and you
are not smiling and messy with corn starch goo at the end, then you are
definitely doing something wrong. Also keep in mind that this is not
just about fun, there is some pretty amazing science going on here.
You will need:
- Cornstarch (a 16 oz. box is good for every 2-3 participants – but more is always better)
- Water
- Food coloring (we always say it’s optional, but it does make it more fun – don’t use too much or you could end up with colored hands…and clothes…and curtains)
- A large bowl
- A camera – you’re probably going to want to take pictures.
Everyone should roll up their sleeves and prepare for some gooey fun.
- This is easy. Pour the cornstarch into the bowl. Don’t rush to add water – take time to feel the cornstarch. Cornstarch does not feel like any other powder. It has a texture that can be compared to that of whipped cream. The grains of cornstarch are so small that they will fill into grooves of your fingerprints and make the prints stand out.
- After you’ve taken-in the feel of the powder, it is time to add water. (You should add the food coloring to your water before adding it to the powder.) There are no exact formulas regarding how much water to add, but it will end up being about 1/2 cup (120 ml) of water per cup (235 ml) of cornstarch. The secret is to add the water slowly and mix as you add it. Don’t be shy here – dig in with your hands and really mix it up. This is usually when you notice that this is not your average liquid. Add enough water so that the mixture slowly flows on its own when mixed. The best test is to reach in and grab a handful of the mixture and see if you can roll it into a ball between your hands – if you stop rolling it and it “melts” between your fingers – success!
We’ll get the the science soon, for now just dig in and explore.
Notice that the goo does not splash (or even move) if you hit it
quickly. Squeeze it hard and see what happens. How long can you get the
strands of goo to drip? What happens if you let the goo sit on the table
for a minute and then try to pick it up? How does it feel? Hows does it
move? Try bouncing a ball on the surface of the cornstarch. You get the
idea – explore!
30 minutes later…
So now goo is everywhere and you’re thinking you should probably
start cleaning. Actual clean up of the goo is a snap. A bucket of warm
water will quickly get it off your hands. It will brush off of clothes
when it dries, and it is easily cleaned off surfaces with a wet rag. Important:
Make sure you do not dump the goo down the drain – it can get caught in
the drain trap and take the joy out of your day of science. Dump it in
the trash, or even mix it into soil in the garden.
Cornstarch grains under the microscope
Now for the science…
Our
cornstarch goo (sometimes referred to as “oobleck” from the Dr. Suess
book) is what scientists call a “Non-Newtonian” liquid. Basically, Sir
Issac Newton stated individual liquids flow at consistent, predictable
rates. As you likely discovered, cornstarch goo does NOT follow those
rules – it can act almost like a solid, and them flow like a liquid.
Technically speaking, the goo is a SUSPENSION, meaning that the grains
of starch are not dissolved, they are just suspended and spread out in
the water. If you let the goo sit for an while, the cornstarch would
settle to the bottom of the bowl.
So why does this concoction act the way it does? Most of it has to do
with pressure. The size, shape, and makeup of the cornstarch grains
causes the cornstarch to “lock-up” and hold its shape when pressure is
applied to it. People have filled small pools with oobleck and they are
able to walk across the surface of it (as long as they move quickly.) As
soon as they stop walking, they begin to sink.
I hope you get to try this out. Have fun exploring!
-Science Bob
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