Monday, February 27, 2012

Building Bridges

  Some families like pinewood derby... we are not one of them. 

 However, we do like a good bridge building, and subsequent crushing. 
Ever since Jennifer began Physics last fall, Mark and I (OK, not so much Mark) regularly ask Jennifer when they are going to do bridges. The minute she found out she texted me. We gave her instructions months ago to make sure she gets an extra set of wood and glue.

 Christian built his first bridge as a junior in Physics and his second, a year later in AP Physics. We learned on his first bridge that you cannot get the same kind of glue at any store in town and the other types of glue just do not work as well - very slow drying = lots of extra time and glued fingers. His second bridge was 6th overall in the school.

Students buy a kit consisting of 3 ft. long and 3/32 of an inch square balsa wood sticks, glue, a cardboard piece and two wood blocks. They are given  instructions with formulas and information about the pressure each piston will put on their bridge. From this they create and draw their design, cut and glue the beams, and put it all together. As they proceed they are allowed to ask the teacher questions about what makes a good design and are given general answers if they ask the right questions. 

The actual building of the bridge is a long and tedious process but rewarding in the end if you are willing to pay the price. 

The bridge is judged by a ratio of how much the bridge weighs to how much pressure it holds before it breaks. Both regular and AP Physics are tested together with the top 5 in the school receiving cash prizes and the top 5 in the state getting more awards. 

With many of the bridges you can tell that they just threw things together. In general if they just follow the basic concepts and the design given to them, their bridge will hold 1000 lbs... the minimum for an A, taking the ratio into consideration. 

The contest is sponsored by BYU and a Physics professor comes out with his bridge crushing machine to test the bridges. He's pretty funny, and comments on the design of the bridge when he puts it in the machine. When he picked up Jennifer's he said something like, "Wow this is really nice! You can tell what kind of grades Jennifer gets just by looking at this bridge!" 

In the end (as you can see above) it held 1443 lbs. with a ratio of 36.something.
She ended up 5th overall!
(If you want to see the video of the bridge crushing you can check it out on Facebook, both Mark and I posted it.)


When her friend in the class found out they were doing bridges she told Jenn that her family had been dreading it since she enrolled in Physics.

I guess we are just weird.