This brass ball fits easily through the matching ring when they are both at room temperature. Heat the ball in a flame, and it expands so that it no longer fits through. Challenge your students to predict what will happen if you heat the ring instead!
Hint: Think about enlarging a photograph.
With the ball and ring comes a data sheet that provides instructions and an explanation of the properties at work in this experiment. The data sheet also includes a list of related products to help with this experiment and other lessons on temperature change, thermal expansion and the laws of thermodynamics.