Memory Spring http://physicstoys.blogspot.com/p/physics-toy-store.html Some special alloys of brass can be made to have a shape memory triggered by temperature. These springs quickly change their length from 1 cm to 2.5cm when heated above 90 C (done here with hot water) and just as quickly shrink back to original size when cooled (immersed in cold water). Useful in many applications, especially things like automatic fire sprinkler valves. This amazing property is probably due to a solid state p