Tuesday, May 13, 2008


With the sodium acetate demonstration for the 5th/6th grade class I also built a rig to demonstrate the properties of oobleck. I took the sub woofer out of a powered speaker system for the computer. I built a cone using resin and fleece fabric (I have seen that done on Pimp My Ride for speaker cases). I also built a 4 inch high flanged ring. To the bottom of the ring I affixed model airplane wing covering. For the sound I found MP3 files at various frequencies.

Oobleck is a mixture of corn starch and water. In the right mixture it crumbles under stress but flows when not stressed. On top of the 60Hz frequency it stands up and dances. There are various videos on Youtube of dancing Oobleck.

To start the demonstration I had three volunteers from the class mix three white powders with water. The first was flour and water, pancake batter. The next was powdered sugar and water, icing. The last was the corn starch and water and everyone could see it was acting differently. Especially when it is held upside down for a short time over a child's head.

Next I loaded it in the machine and showed standing waves at lower frequencies, but the fun really starts at 60Hz.

I had fun making the rig. The kids all had fun watching the oobleck dance and making a sample of oobleck to take home. I didn't hear from any parents who were uhappy about the mystery substance that the kids came home with.

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