Ball-and-Ring Thermal Expansion

A tiny temperature change can stop/start the fit. Ask students to predict what will happen. Show ball fits cold; warm ball or ring as apparatus permits. Key idea: Metals expand when heated because average atomic spacing increases. Ask: How can something get bigger without adding material? Safety and cleanup: Teacher handles heated metal; avoid flames if possible. https://www.youtube.com/watch?v=QNoE5IoRheQ