lew (04/19/83)
Yes, rubber has a negative thermal coeffecient of expansion. Hang a small weight from a rubber band and bring a match (lit, of course) near to the rubber band. The rubber band will contract and the weight will rise. An easier demo is to stretch a rubber band, wait five seconds, place it against your upper lip, then let it relax. You will feel a definite cool sensation. The "rubber band equation of state" is an old standby in statistical mechanics. The band is modeled as a long chain. The joints between links can be either folded or open. The length of the chain is then given by the number of open minus the number of folded joints. This gives a certain density of states for each length etc. etc. Lew Mammel, Jr. ihuxr!lew
emma (04/20/83)
There is another rubber band demo, which I've always thought is kind of fun. Take a bicycle wheel and hub, and replace the spokes with rubber bands. Now shine a heat lamp on one side and watch it turn. -Joe P.