At the end of term I always like to do the beer foam decay lab. I bring some crisps to go with the beer and have a bit of an end of term party. I used to do this experiment by sticking bits of paper to the cylinder and marking the progress of beer with a pen, however it's much better recording it on video which can then be analysed with loggerpro. This also means that you don't need so much beer. In the photo 5 computers are recording the exciting event at the same time. Two of the students in the photo are visitors from the Laski school for the blind in Poland. I really wanted to use something that they would be able to experience more easily so was thinking of using popcorn. This idea was abandoned after watching a youtube clip and realising that popcorn does not pop exponentially. Anyone got any ideas for an exponential decay you can hear?

I should add: The beer is non alcoholic and any way, the students don't drink it.