"Conservation of Momentum" in a Transition to Physics First

Two teachers at the same school facilitate essentially the same lab activity, but with different levels of commitment to the process of inquiry.

In a time of transition from a traditional BCP sequence to a Physics First sequence, schools or districts are often faced with a distinct challenge of limited personnel. A ninth grade physics class is fundamentally different from both a ninth grade biology class or a physics class directed toward juniors or seniors, and very few teachers have direct experience teaching Physics First. In the switch to ninth grade Active Physics in the San Diego public schools, for example, the transition was driven mostly from the top down, with grossly inadequate professional development to prepare teachers for the task they were undertaking. Many biology teachers were simply ordered to become physics teachers, and physics teachers who had no experience with younger students were dropped into a project-based curriculum with little quantitative emphasis. The program was doomed to fail from the beginning, and San Diego switched back to BCP five years later.

Much of the time, however, the remnants of a switch to Physics First can be more more subtle. I visited a public school near Philadelphia that offers a Physics First track as an option for high-achieving students. The majority of ninth graders take environmental science. During my visit, I saw observed two sections of physics for ninth graders, both based in Modeling Instruction but taught by different teachers. The same basic lab activity was carried out in each class - both labs involved the use of a track with two carts with photogates mounted to measure the speed of a cart rolling toward either end of the track - but there were important differences between the classes.

At the beginning of one class, the teacher wrote a simple prompt on the board: "Objective: graph ∆Pbluecar vs. ∆Predcar" and showed students examples of possible interactions between the carts (bouncing, sticking, etc.). Students set to work putting together the apparatus, making measurements, calculating values, and eventually, plotting these values on a set of axes.

In the other class, the teacher gave students a worksheet on which to record the results of three specific collisions (bouncing with both carts moving toward each other, bouncing with one cart still, and sticking with one cart still). After all students had completed the required calculations for each collision, he asked students to tell him the results of their collisions and wrote each group's result on the board. He then told students:, "Something needs to be true about those initial and final momentums. If you didn't get this, there will be a lot of things wrong when I correct this lab... This is the goal for this unit." The teacher then wrote "pi = pf" on the board, and explained the details of conservation of momentum to his students while they sat in their seats.
 
Both of these classes served as the introduction to the same Modeling-centered unit on conservation of momentum, yet it seems to me that only one of them held true to the priorities of inquiry-based instruction. It's relevant that the first class was taught by a teacher whose Modeling Instruction training came early in his physics teaching career, while the second was taught by a seasoned physics teacher with many years of experience teaching AP. I learned in talking to this second teacher that the science faculty were a major force behind the decision to choose Modeling Instruction as a curriculum for their Physics First classes, but (on the basis of this one brief observation) the Modeling training they both received impacted the younger teacher more deeply than the older teacher.

At the end of my visit, I spoke with another teacher at the school who is teaching a "Pre-Chem" course for lower-track students, consisting of three units of Modeling chemistry combined with a less-quantitative introduction to five units of Modeling physics. (This teacher is also a Modeling Instruction summer workshop leader.) We talked about the complexities of transforming one's own teaching style, and the role that various teachers have played in the broader transition to Modeling at this school. It's clear that a successful transition to Physics First requires strong administrative support, but administrative support is no help at all if the teachers themselves are not committed to the classes they are teaching. Perhaps the successes of the program at this school are due in part to the flexibility of everyone involved to adapt to a wide range of teaching styles and expectations through this transitional period.