Sunday, November 28, 2010;
My son's third-grade teacher invited fathers to visit the Rockville class and talk about our jobs. A grown-up show-and-tell, circa 1991.
I'm a scientist and can easily get dry ice, a perfect prop for a demonstration. Plus, I know a cute trick: Put a pellet of dry ice in an inch-long plastic sample vial, close the snap-on lid, and set the vial lid-down on a table. The solid pellet turns to gas, and the pressure builds. After about 30 seconds, there is a loud pop, and the vial rockets to the ceiling.
The first part of my show went well. I explained that dry ice (solid carbon dioxide) sublimates to a gas, and I loaded a vial. The rocket launched, pinged off the ceiling, fell harmlessly, and everyone clapped.
I should have stopped then.
Instead, I asked the students whether they wanted to make their own rockets! The teacher's jaw dropped, but it was too late. We went outside. I gave each kid a vial, spread the dry ice on the playground, and told them all to be careful.
The girls were careful. The boys immediately realized that the loaded vials could be used as weapons by launching them at an angle. Rockets flew in all directions. Kids yelled happily, oblivious to danger. The chaos stunned me. Fortunately, the teacher quickly took control before anyone was hurt. She thanked me. I thanked her.
Lesson learned: Don't give inexperienced people rockets.
Richard Pastor, Potomac
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