The classic cast iron Bar Breaker is a device that demonstrates the unstoppable forces of expansion and contraction. A steel bar lies in a cast iron frame and a cast iron pin locks the bar in place. A gas burner is fitted into the cast base and heats the bar. As the bar expands, it tries to bend the cast iron rod. Finally the cast iron pin breaks with a loud report. With the steel bar hot, another pin can be fitted and locked. As the bar cools and contracts, again the cast iron bar is broken with a loud report.