Making Quicksand

Well today we made quicksand using the tried and true home experiment of cornstarch mixed with water and (for effect) food coloring.  We victimized, largely for effect again, one of The Crew’s lego men, who seemed none-too-happy about being dunked in quicksand.  They had a great time exploring all the physical properties of it, how if they moved the lego man quickly through, he get “stuck”, but if they slowly dragged him through he could flow gently through the “liquid”.  Their favorite part (and mine as well) was that if they took a glop of our blue goo and quickly balled it around in their hand, it would make a stiff ball, but as soon as they stopped forming the ball, it would revert back to liquid and ooze through their fingers.

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So what is quicksand anyway, well in short, it is a mixture of a solid and a liquid in a colloidal suspension.  In our case it is starch molecules evenly interspersed among water molecules; in the old western movies, it is the same concept but sand molecules amongst water.  The reason we could “ball” our goo into a solid is that with quick force and constant movement, the relatively larger starch molecules bump into each other, trap the much smaller water molecules and create the characteristics of a solid.  When the movement stops, the starch molecules are allowed to once again flow through the liquid, and the suspension retakes the characteristics of a liquid.  This is a little different than quicksand in nature, where the ratio tends to be more solid (sand) and it is the rapid movement of someone trapped in quicksand that cause the sand to flow more and bring on characteristics of liquid.