Bridge Post: Final
Peter Carbone
Patrick Antonelle
May 9, 2012
AP Physics B – Period A
Final Bridge Blog Post
As the project for our fourth quarter, our AP Physics class constructed model bridges out of balsa wood. Each group of two students was tasked with constructing a bridge with the materials provided. The main goal was to erect a structurally sound bridge that could support as much weight as possible.
Our group, (Peter Carbone and Patrick Antonelle), planned to use our design from the USMA bridge program as the basis for our balsa wood structure. One of the most integral parts of our bridge was the pier; it provided much needed support in the middle of our bridge. Unfortunately, it was impossible and implausible for any groups to use a pier-like structure so we were unable to use the USMA bridge design. However, we were able to takes some aspects form it, such as the truss system.
Our original design for the balsa bridge was a truss on the topside of the roadbed, and another, shorter, truss system underneath the roadbed. As we proceeded to building the bridge, we found that the truss systems that we had in place lacked functionality and sufficient strength. Moreover, we amended our designs and decided to only employ a truss system on the underside of the roadbed. The main function of the underside truss system was that, as weight was added to the bridge, the roadbed would flew downward, pushing out the ends of the truss system and thus bracing them against the placement apparatus. We liked this idea because we felt that it would provide for increased strength and stability.
Upon testing our bridge, we were pleased with the results. After our teacher Mr. Love added about 165 N (~ 16 kg) (~ 36 lbs.), the bridge’s roadbed and truss system snapped. [As you can see in the picture below]. The failure happened towards one end of the bridge; the roadbed collapsed under the compression force as the truss system buckled from the tension force. The main problem was that only one side of the truss worked as planned in that it braced against the holding apparatus for further support; the other side did not quite touch, and that was the side in which the bridge failed. If we could have changed anything, we would have added another long piece of balsa wood on top of the roadbed, thus increasing it thickness and enabling the bridge to endure more compression. Also, we would have fixed the one side of the truss so it would have braced itself successfully.
Throughout this project, our group had to keep a couple things in mind: Newton’s Second Law of Motion (F = ma) and the equation for pressure (P = F/A). Knowledge of these equations allowed our group to understand the relationships between force, pressure, area, and mass. The most important concept that we understood was that there must be an even distribution of force over a large area in order to reduce the pressure on the bridge.
In conclusion, with the materials provided, our duo (Peter Carbone and Patrick Antonelle) was pleased with our bridge. There were a few things we could have added to our bridge or changed in order for it to hold more weight, but in the end, it held its own pretty well. We worked hard, thought hard, and built hard; we employed as much knowledge as we could into the building process. Unfortunately in the end, like many other fellow groups’ bridges, our bridge “cracked under the pressure.”