School of Physics Lecture Demonstration Manual

Hb-2 The Bar Breaker

Published: Monday 13 March 2006 - Updated: Monday 28 March 2011


To demonstrate the force of contraction.



Click on pictures to enlarge.

Bar Breaker Diagram


A strong iron bar is constructed so that it rests in two yokes on a cast iron base. The bar is pinned on one end by a thin cast iron pin, and threaded on the other end so that it can be tightened. The bar is heated via the gas jets located directly beneath the bar. The bar is tightened as it is heated. After the bar is fully tightened it is dowsed with water and as the bar contracts the forces present are large enough to snap the cast iron pin. There is a delay between initial cooling and fracture of up to 30 seconds.

Safety notes

Sharps Safety 


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