I was on the look out for new ideas for demonstrations to do with kids. A new one for my dry ice repertoire is the smoke ring device featured in the video below.
There were public performances by Doctor Kaboom and Mr. Freeze from Fermilab.
One challenge of such performances is to go beyond "wow" and "gee whiz" to trying to teach something about how science works.
Dr. Kaboom tries to do this by testing a hypothesis about why the catapult was invented (video). However, I thought it was a little drawn out and was not sure if the point got through.
Mr. Freeze has a host of demonstrations based on liquid nitrogen. The one with the exploding cardboard box is pretty cool (video).
He also has a nice demonstration to show how the volume of a gas is about one thousand times larger than the volume of the liquid of the same amount of material. This involves using a 44 gallon garbage bag, shown below.
The demonstration is important and useful for at least two reasons.
For kids demonstrations this important fact is the key to many demonstrations involving rockets or explosions. One example, is baking soda rockets which are based on the production of CO2 gas.
For undergraduates, this thousand fold difference is the basis for using the Clausius-Clapeyron relation to explain why the slope of liquid-gas phase boundaries is much less than solid-liquid phase boundaries in pressure-temperature diagrams.
Trivia I learnt was that Fermilab uses thousands of gallons of liquid nitrogen per day, but this is less than McDonalds!
I find it a little ironic that one major part of Fermilab's public outreach involves condensed matter demonstrations.
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