Okay, back to science! I'm doing a couple of little surface tension experiments with the 9th graders today. The first one is a simple demonstration. Fill a glass with water all the way to the top, and then gently drop in marbles until the water level is above the edge of the glass. What's holding the water in that dome shape and keeping it from falling over the edge is surface tension.
The second one is more fun for the kids. We've got a little tray with about an inch of water, and a small fleet of cardboard boats (which are really just pentagons with a little rectangle cut out of the back). A drop of soap in that cut-out slit propels them forward. Zoom!
We only have about 10 boats for 25 kids, so we pick them randomly. They've got a little box filled with wooden ice cream spoons (like popsicle sticks) with their names on them, and we draw out one at a time. Some of them miss the slot and then the boat can no longer move because the surface tension is equally decreased on all sides of the boat. We explain why you only get one chance, and they seem to understand.
Srinivas, one of the computer teachers, comes in a little late to observe. He's young - he's 19 and still doing his Bachelors degree - and enthusiastic. So when one of the students misses the slot, he tries adding more soap, and the kids laugh and tell him it won't work because the soap has dispersed through the water. It looks like they really do understand. Cool.
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