High school students should know that matter cannot be created or destroyed. Therefore, when an object expands because of being heated, it does not increase its mass. Instead, the average amplitude of the vibration of the atoms that make up the object increases. This causes there to be more space between atoms, and as a result, the object expands. Similarly, the atoms of a cooling object decreases vibration intensity and therefore contract. Students are probably able to conceptualize liquids expanding, but may have more difficulty picturing solids doing the same thing.
The materials required for this experiment include a Bunsen burner, beaker of cold water, and a metal ball and ring made specifically for this purpose. Both the ring and ball should be attached to shafts to make handling them easier. Other objects can be used for the demonstration if they do not fit together without being heated, of fit together when room temperature but not when heated. Examples may include closely sized washers and bolts.
Demonstrate to the class that the ball easily fits through the ring. Turn on the Bunsen burner and heat the ball for one minute. Try to put the ball through the ring again, showing the class that it can't be done. Place the ball in the beaker of cold water for one minute. Put the ball through the ring again. Ask the class why it is not possible to put the heated ball through the ring.
Point out everyday examples of solids expanding and contracting from temperature changes. Instances include telephone wires, since they are hung loosely to contract in cold weather and can be seen to sag in hot weather. Ask students why a metal lid that is difficult to open should be heated for easier removal. This may also be a good time to introduce the concept of linear expansion coefficients, which are the accepted measurements that solid materials expand.