The collapsing can demo is one I loved seeing for the first time when I was at school, although my teacher used a tin with a screwed down lid which took a little more time to cool down. In some ways I prefer the version using a can with a screw lid because the additional waiting time makes for an even more dramatic “collapse”. Doing the demo with a drink can is of course far cheaper (and I think, more reliable as it doesn’t depend on the lid being screwed down properly) and I suspect this is why the approach we use in our video has become far more widespread in schools.
I like the demo a lot but, as I hope we’ve managed to convey in the video, I think we need to be careful how and why we use it in our lessons. This is a really fantastic demo for using the Predict, Observe, Explain (POE) approach as the explanation of what’s going on is not entirely straightforward – there are a couple of things relating to the behaviour of particles and the action of forces that need to be considered and this can lead to some really interesting discussion with students, providing they’re familiar with the relevant concepts.
We’ve suggested in our video that the collapsing can demo can be used in conjunction with another demo, as a way of “scaffolding” (I really hope I’ve used that term correctly – I think this may be the first time I’ve used it in writing in this context).
Once you’ve done the demo live in class, you’ve got the perfect justification for showing your students this video of a rather more spectacular demonstration of the same physics at work:
This film was produced for the Get Set Demonstrate project. Click through for teaching notes, and take the pledge to perform a demonstration to your students on Demo Day, 20th March 2014.