Day 107: Collisions & Test Design

AP Physics: Collisions

Students use a pair of Direct Measurement Videos, one of a collision between two billiard balls and one of a heavy disk tossed onto a cart, to explore changes in momentum and kinetic energy in the collisions. I haven’t done as much with uncertainty as I’d like, so I was very pleased with how clearly students were talking about it to decide if their values were “close enough.” I had students sketch momentum SOS and energy LOL diagrams, but students weren’t paying as much attention as I’d hoped to whether there were any dissipative forces present, so next year I want to do a better job of getting students into that habit. I was thrilled, however, when a student used some proportional reasoning to convince herself that you cannot conserve momentum and keep a constant kinetic energy when the objects are moving together after the collision. I was also pleased by how many students were interested in trying to explain the billiard ball that just spins in place right after the collision.

Physical Science: Test Design

Students began working on designing a second iteration of their cargo carriers. To encourage new designs, I increased the cost of paper cups (the most popular component on the first round) and shuffled groups. We also talked about the limits of testing just the front-end collisions, and tasked students with coming up with their own tests for this round. The discussion was a little trickier this year than in the past; we dramatically upgraded the trucks the cargo carrier attaches to this year and the old trucks would pretty reliably tip over or roll off the side of the ramp at least once per class, which gave a nice tangible example of the test’s limits. That didn’t happen at all this time, so next year I might take off the rails we put on the side of the ramps to try to encourage some failed tests.