H.2(1) – Ball and Ring
This is a simple demonstration of metal expanding when heated and contracting when cooled. When both the ring and ball are at the same temperature, the ball can easly pass through the ring. Heat the ball over a flame for a few seconds: it will not pass through the ring. A similar effect is demonstred when the ring is cooled, dipping it in liquid Nitrogen, for example.
H.2(2) – Unequal Expansion Bar
The bar consists of a strip of brass and a strip of Invar steel each 25 cm long, cemented together and mounted in a plastic handle. It demonstrates the unequal expansion of metals. At room temperature, the bar curves slightly towards the brass side. When placed in the burner’s flame, the bar will bow vigorously the other way, only to reutrn to its original shape when allowed to cool off. This property is used in the construction of thermostats.
