I visited SteelyKid's first-grade class yesterday with several liters of liquid nitrogen. Earlier in the fall, they did a science unit on states of matter-- solid, liquid, gas-- and talked about it in terms of molecules being more spread out, etc. Looking at her homeworks, I said "Oh, damn, if it wasn't the middle of the term, this would be a perfect excuse for liquid nitrogen demos..." I mentioned it to the teacher, though, and she loved the idea of having it in December, as a call-back to earlier science lessons.
It turned out to be weirdly difficult to find assorted round latex balloons yesterday morning, so I was a little frazzled by the time I arrived, but it went well. I started off by putting some liquid nitrogen in a bowl and dropping in a snowball, so they could see that the snow made it boil furiously. I explained that this was because compared to the nitrogen, snow is red hot.
The teacher was rightly concerned about keeping the kids back from the demo table, so she said "Wow! If it's that cold compared to snow, is that something you want to get on your body?" All the girls dutifully chorused "No!" but about half of the boys said "Yeah, let's see that!" So there's your gendered socialization moment for the day...
Anyway, if you've got legitimate access to liquid nitrogen and a first-grade class, I recommend taking the former to the latter and showing it off, because they were a riot. Stuff I did:
-- The snow in nitrogen thing
-- Froze a few ounces of water in a plastic bottle by dunking it in a bowl for a few seconds
-- As suggested by Rhett Allain, I put a couple of pinholes in a ping-pong ball, and dunked it in liquid. A bit of nitrogen got inside, and when I took it out and put it on a table, it started spinning. This would've worked better with slightly bigger holes, and a colored strip or other marker on the ball, but they got a kick out of seeing it move around.
-- I packed four balloons into a dewar that should only have been able to hold two. Then I pulled out the flattened balloons, and four others I had loaded in before they got back from lunch.
-- I broke a frozen squeaky dog toy. Unfortunately, the ones I got this year were a little more robust than the previous batch-- they were foam-filled under the rubber, so it cracked and split, but wouldn't shatter.
-- I brought a bunch of cheap flowers from ShopRite, and let each kid come up and freeze one, then smash it in a trash can. Which was, of course, the biggest hit of the event.
I did have to dissuade one boy in particular from trying to put his hand in the liquid, though I knew that was coming from him (he was in SteelyKid's class last year, too...). All in all, though, they were very well-behaved, and recalled a good deal of the science stuff from earlier in the year, so that was great to see.
And SteelyKid beamed like a quasar jet through the entire thing, so it would've totally been worth it even if none of the other kids got anything out of it.
I did not, however, get any pictures or video to attach to this post, so in lieu of that, please accept this link to Jefferson Lab's Frostbite Theater collection of videos of cold stuff.
I can practically see the elation and pride on her face..............you are and will always be her hero!