STEMNET Science, Technology, Engineering and Mathematics Network

I was first put on to Science Busking by my second daughter, who has just qualified as a Chartered Chemist. It's a bit like Street Magic, only for real; you perform the apparently impossible right under the noses of members of the public.

I got the chance to do a bit at the Three Counties Show in June, at the STEM stand. All the "tricks" illustrate odd or counter-intutive aspects of natural laws, and some are real crowd-pullers.

One stunt used a home-made drum with a fist-sized hole in the bottom, and a light curtain of thin plastic or fabric strips, like those you sometimes see at the doorway of a kitchen. You stand up to four metres away from the curtain, aim the hole end of the drum, and pat the drumskin hard; the resultant vortex of air flips the curtain even from that distance.

Another involved pushing a sharp stick through a balloon without deflating it - always terrifies the young punter you get to do it; another used a hair-dryer to float a light ball around the stand (not just over the nozzle!) and others demonstrated the peculiar properties of a container full of small solid particles, like beans.

One of the latter demos never failed to impress. A large bowl full of smooth dried beans, when swirled, acts like a fluid. Something heavier will sink to the bottom of it, and something lighter will float to the top. We used large metal ball-bearings for the first part of this - they stayed on the top until you got the beans moving, and then they vanished in seconds. That was neat, but not entirely unexpected; what really blew people away was the second part. We buried ping-pong balls under the beans, got the student to swirl the bowl around - and watched the astonishment as the ping-pong balls appeared on the surface!

My overall favourite, though, was the two-ball trick. You take an ordinary football, and a small, light plastic ball, and first demonstrate that neither of them is particularly bouncy - dropped from chest height, either one will only bounce thigh-high. Then you carefully line up the small light ball exactly on top of the football, and let them both go. The football does an even smaller bounce than before - whereas the little ball heads for the moon ! It's the conservation of momentum, of course - the "bounce" is passed on from the heavy football, and mass x velocity has to stay the same ... We didn't quite punch a hole in the marquee, but it was close.

So if you want something a bit different at your next school fair, or science event - get in your local STEM team, or an Ambassador who has the kit to hand. And have a go yourself - it's immense fun !