Friday, August 23, 2013

When Cornstarch Attacks

I was thinking back to some fun experiments that I did when I was a kid and remembered this little trick with cornstarch. It also amuses college students and people of all ages. Be sure to ask your parent or guardian before you make the glop! The only ingredients are cornstarch and water. Pour the water into the cornstarch slowly while mixing until it flows. If you put it on an old speaker (BE SURE TO ASK YOUR PARENTS, FIRST!), the glop dances like this.
This mixture is a non-Newtonian fluid. Contrary to the video, this just means that the stresses that are making the material flow are not proportional to the actual flow (the shear strain rate) at a given point. As the particles of corn starch are moved past each other, they catch on each other. The faster you try to move them against each other, the more they catch on each other, making it more difficult for the cornstarch to flow. The property that is used to describe something's resistance to flow is called viscosity.

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