AP Physics: Where Does the Energy Go

This week, students started working on an activity to figure out what interaction causes energy to dissipate as a bouncy ball bounces (I wrote this up for The Science Teacher a few years ago). After observing a bouncy ball, students agreed that some combination of the impact with the table and the air resistance on the bouncy ball are responsible for the energy dissipating, so now their task is to figure out which it is. I spend a lot of time priming students for what evidence might be useful and we started late in the week, so we mostly focused on making one set of energy bar charts for if only the impact dissipates energy and one set for if only the air resistance dissipates energy using five key points along the bouncy ball’s motion (right as it’s released, right as it reaches the table, right as it leaves the table, at the top of the first bounce, and right as it reaches the table a second time). I forgot to get a picture, but one group did a cool thing where they labeled which interaction was happening between each of their bar charts to help keep track of when the dissipated energy should show up. We then had some good discussion about what these energy bar charts tell us we will actually observe in the lab.

Physics: Math Sensemaking

This week felt a little goofy. The other physics teacher and I are doing the same activities on as close the same day as we can so that we can plan together (a key survival tactic when both of us are also doing what are supposed to be full-time jobs outside the classroom!). He is out this week, so we used several Pivot Interactives activities to wrap up forces and introduce momentum (full disclosure: I work for Pivot writing activities). As I worked with students, two big things that aren’t directly tied to the science content ended up at the front of my mind. First, students told me their biggest frustration with the Pivot activities is they had to measure carefully to get the autograded questions correct. I think this fits with where students believe that physics knowledge comes from. When students see experiments, observations, and measurements as where physics knowledge comes from, I find that students tend to measure more carefully because they see a purpose to having good-quality measurements. Combined with some other things I’ve observed about my students, I think many of them see me as the primary source of physics knowledge in the room, so why should it matter whether they measure carefully?

Second, I saw a lot of evidence that students are not attaching physical meaning to their measurements. This was most apparent to me in an activity where students used Newton’s 2nd Law to determine the mass of an unknown object. Students were able to measure the net force on a system that included two gliders and the mystery object as well as make measurements to determine the acceleration of the system. Once they calculated the total mass of the system, a lot of students really struggled with how to use the given mass of the gliders to figure out the mass of the mystery object. This made me think of the work some of my grad school classmates and professors have been doing around blended sensemaking in science (here’s a taste), which is a term for simultaneously doing sensemaking in science and in math. Recognizing they needed to subtract the mass of the two gliders from the total mass required students to recognize what the mass they had calculated represented, how the given mass of the gliders relates to the mass they had calculated, and what the operation of subtraction represents in this context. Doing all of that can be some pretty tricky blended sensemaking! Realizing how much my students are struggling with this is helping me make sense of some of the other struggles I’m seeing in my class right now. I’m not sure what my fix is yet, but I definitely want to keep thinking about how to support students in attaching meaning to numbers and doing blended sensemaking.