Spectacularly bad timing, but fun anyway

Looking around for a Fascinating Demo, I decided to try bringing in some dry ice, or as I prefer to call it, frozen Carbon Dioxide.

As I'm proudly unveiling my little stroke of genius, there's some rumble around the room about "already seen this". It seems I'm the only guy on the planet who doesn't know about the very gracious class grandfather (UT Physics prof) who visited just yesterday. He had frozen CO2. He had liquid oxygen. He had liquid nitrogen. He had a whole Physics Circus. Oh boy. Here I am with my little sack of dry ice from HEB. Yesterday's Physics Circus included demonstration involving balloons. And guess what's in my hip pocket: a sack of party balloons.

I don't know when I've had worse timing than this.

Well, we went on with the show anyway – after all, dry ice is fascinating enough to see more than once. Also, as far as I could tell, my little demo (fill a test tube with dry ice. Stretch a balloon over the top. Watch the balloon expand as the CO2 turns from solid to gas) was actually not something that had been done the day before.

It worked.

The balloon inflated so well, we segued to an unplanned second demonstration. I tied off the CO2-inflated balloon, then carefully inflated another balloon to exactly the same size. Of course CO2 is heavier than air, so the balloons should not weigh the same. Drop them from 6 feet up at the same time, and the CO2 balloon reaches the floor first!

I like it as a demonstration, even if it totally sabotages what they're going to hear about Galileo and the leaning tower of Pisa next year.

Questions are thinning out. I think everybody has End Of Year- osis. (Senior Slump?) . There were two about "why is [other student's name] so nice", which I considered mangling into a whole session on Altruism and evolution - - having just finished reading The Selfish Gene, complete with its startlingly optimistic chapter on the evolutionary basis for trust and cooperation. Maybe next year.