I remember I first did this experiment during my undergraduate Physics lab class with my lab partner (who did most if not all of the work because I was absent the previous session). I liked it because it was easy but opens up discussions about viscosity and force and it’s so easy, kids can do it with some supervision.
What you need :
- Corn starch
- Glass bowl
- Paper towels for cleaning up
What to do :
Cover your work area with paper towels for easy cleaning.
.Prepare the stirrer and bowl for mixing and add 1/8 cup of water.
Measure ¼ cup of dry cornstarch and add it to the bowl.
Stir and add more water or cornstarch until you get the right consistency.
What to expect :
My kids had so much fun mixing that they want to do the experiment again and again.
While mixing, you will know you got it right when the mixture becomes hard when you press on it (or apply force) and it feels solid yet you are able to keep mixing it like a liquid or touch it like a liquid when you do not use much force.
You can hold it like play-doh, my daughter says.
Scoop the cornstarch mixture into the palm of your hand, then slowly work it into a ball. As long as you keep pressure on it by rubbing it between your hands, it stays solid. Stop rubbing, and it “melts” into a puddle in your palm. Can you think of other tests you can do with it?
Why it happens:
Most fluids behave like water and honey, in that their viscosity depends only on temperature. We call such fluids “Newtonian,” since their behavior was first described by Isaac Newton (when he wasn’t discovering the laws of gravity or developing the calculus). The cornstarch mixture you made is called “non-Newtonian” since its viscosity also depends on the force applied to the liquid or how fast an object is moving through the liquid.
Afterwards, we asked our daughter to to find out who Newton is from her encyclopedia and find out about the Law of Viscocity.
Newton stated that the viscosity of a fluid can be changed only by altering the fluid’s temperature. For example, honey flows easily (low viscosity) when you warm it but becomes very thick (highly viscous) when it gets cold. A non-Newtonian fluid doesn’t have the same dependence on temperature because its viscosity changes when stress or a force, not heat, is applied. When you squeeze a handful of the glop you made, the particles of cornstarch come closer together and trap the water between them. Its viscosity increases and it acts like a solid… for a split second. When you release the pressure, water fills the spaces between cornstarch particles again and the glop behaves like a liquid.
We finished up with that but if you’re interested in more complex (more fun!) experiments, try Electric Cornstarch. Let us know how it went for you by dropping us a comment below.
Hope you had fun watching our video and learning about science!
Watch out every Saturday for more Science experiments, field trips, and discussions with these two!
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References and thanks:
3. Special Thanks to Bensound for the Music in our video. http://www.bensound.com/royalty-free-music/track/energy