The Physics of Bridges

Class III Physics students recently competed in a bridge building competition as part of a unit on engineering. Required to meet certain size specifications, the boys were challenged to build the lightest bridge possible that would support the heaviest load. The bridges had to span 40 cm, be no more than 8 cm wide, and support a minimum of 10kg (about 25 lbs) to be awarded a base score. Additional points were awarded for high quality construction, aesthetics, and weight to load ratio at failure.

The result was a vast array of spans including arched, suspension, and a great variety of trusses. In the end, ten of the structures were able to support the 400-lb load without failing. The lightest bridge to do so (at 81 grams) was designed by Harry Weitzel. It held up under more than 2,200 times its own weight!

In support of this challenge, these same students have been studying the nature of structures, stability, and strength of materials, and as part of the class took a tour of the active construction site currently surrounding the campus. Led by the lead on-site engineer for Shawmut, the discussion focused on the importance of reinforced concrete piers, the three-foot deep steel I-beams (which will span the indoor athletic center) and the large equipment used to move the heavy loads.

 See bridge challenge photos here.