Demo chains Jem

26 04 2012

In a previous post Demo chains were discussed. This is a nice example of a demo chain from Jem Stansfield from BBC One’s Bang Goes the Theory. Instead of telling us about some science and then showing a single demonstration, or showing a single demonstration and then telling us about the science, Jem has crafted a chain of demos. Not only does that chain of demos help us understand better what is going on but it also builds tension and focuses attention on the final spectacular effect.

Apologies for the quality of the video- any complaints should be directed to lilemi98.

Did you see the chain? Firstly we were introduced to the flammable gas- it was burned in the bowl. Then we saw what happened when you use too much fuel- the first rocket was a bit disappointing. Finally we saw what happens when you get the right mix- the final rocket disappeared into the rafters.

This is a very effective treatment of this subject, the props were built to a very high standard and the final effect is impressive even in such a massive venue. Big scale shows are not easy things to pull off but this was done very well.

You could argue that there are enough demonstrations in that piece and that the fundamental science (flammable gas in correct proportions produces the most vigorous reaction) is covered using just those three demos. However more concepts than just those are introduced or referred to in the clip and the event was open to children from 11-18. There is a large difference in what you can assume an 11 year old and 18 year old understands. Perhaps Jem could have added even more demos just to ensure the audience was fully prepared to learn about gas mixes and marvel at their effects?

Different presenters have different presentation styles and Jem does a great job here and on the TV. The reactions of the audience show how interested and attentive they were and how effective Jem’s audience handling was. However, would everyone there have realised that for instance:

a rocket is essentially a big tube and inside it is an enormous, ferocious and continual explosion– this could have been backed by a short video of a rocket burning on the screen over Jem’s head as this was being explained

out in the open air [the flame] isn’t producing any thrust… all the hot gases from that explosion get flung out of the back of the rocket and the rocket gets flung out in the other– have 11 year olds covered Newton’s Third Law yet? And even if they have has everyone fully grasped its relationship to rocketry?  A graphic, a video or even simply letting off a rocket balloon would reinforce this understanding.

at the bottom of this I have an electrical igniter– What is an electrical igniter? What does one of those do? Perhaps Jem could have refered to the lighter he used to set fire to the gas in the bowl or mentioned that it would produce a small spark that would start the reaction.

By far the hardest bit to explain is the way the gases mix- the scientific term is stoichiometryJem uses a metaphor to explain“it’s a bit like an old school dance”. This is effective because it paints a lovely familiar image that seems totally unrelated to the science. But there are again demos that you could do alongside a verbal explanation that might help everybody understand.

The tin in this clip doesn’t explode immediately because the gas mix isn’t right. As the flammable gases contained in the tube burn through the hole in the top of the tin air is drawn to replace it underneath. With that air comes oxygen and when the oxygen/flammable gas mix does reach the right combination… BOOM!

This is straying into the subject of another post Show AND Tell but the combination of verbal and visual would have allowed Jem’s verbal explanation to have been more complicated- catering for the 17 and 18 year olds in the audience studying A-level physics- and perhaps an easier concept to grasp for the younger kids- it doesn’t take off until the mix is just right. It would also have further built up the anticipation of the big rocket and really got everyone’s attention and prepared them for the speed and violence of the final effect.

Thanks to lilemi98 for posting the video and congratulations to Jem for a great piece of science communication. His use of demo chains is a powerful example of how using multiple demos we can help our audiences understand better.

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