Suppose you have a weight hanging from a rubber band and you heat up the rubber band, will the weight go up or down? from grade-school the answer "down" was pounded into my head - obviously - when something is heated it expands! but yesterday i was reading the Feynmann lectures and in the chapter about statistical mechanics he said that the rubberband actually gets shorter when heated. he explained that heating the RB gives it more tension and so it pulls harder on the weight and the weight goes up. but isn't it true that as something is heated it expands? Thanks.