Last weekend saw the ‘Cardboard City’ event at church. Basically, it’s a fun weekend for children. The main event is the construction of ‘houses’ from bits of cardboard, sticky tape and string, in the church hall. Then the children get to sleep in their box houses overnight (supervised by foolhardy and sleep-deprived volunteers like myself). So in the weeks beforehand we accumulated numerous large cardboard boxes (e.g. the ones that fridges and armchairs come packed in – what a consumer society we have…), piled them up (flat of course) in the church hall and had everyone raid them for what they needed.
There were some pretty impressive constructions, I have to say – you couldn’t say the children we had lacked ambition. I reckon one group had a ten-kilo roof on their house – I know because I had to help put it on. As a physicist, constructing things from cardboard is a great showcase for how strong some materials are. The humble cardboard box is made from cardboard that is essentially a sandwich – two flat papery layers with a corrugated paper structure between the layers. The corrugated structure is hard to bend perpendicular to the corrugations, giving exceptional rigidity in a material that has a very low density.
To really get rigidity, you’d stick two sheets together, with corrugations running opposite ways. An alternative is to roll the cardboard into long tubes (tricky – they turn out more like prisms, but it doesn’t matter) – it then takes a lot to bend each tube. The overall result is that, with a bit of effort, over a whole afternoon, you can construct some fantastic buildings with just boxes and tape.
Of course the real fun is in destroying them afterwards, and then the real effort is in tidying up the mess and disposing of fifty mangled fridge boxes.