On one of the hottest days this year my friend's son (seven years old) and I (53 years young) went along to a free event in the Big Blue Shed to make perpetual motion machines as part of the Sheffield Children's Festival. Well, the machines actually were gravity chain reaction machines built by the kids and parents/adults. The event was fantastic. Hosted in a very engaging manner with free soft drinks supplied (we needed them because of the heat) and sandwiches at lunch time. The facilitator and helpers were brilliant! After an enjoyable demo of a large scale chain reaction we all set about building our own gravity machines, the aim to get a chain reaction going for 30 secs. If you remember the Honda adverts with lots of bits of a car knocking over the next bit of a car you'll know what a gravity machine is. Anyway, great fun was had; the machines worked in practice but inevitably didn't when demonstrated to the others! Apparently there should be video footage on the web site.
A highly recommended activity and a great way to spend a chilled (relaxed!) morning, afternoon or day down the BB Shed.