Days 73-74: Projectile Video Analysis & Cart Catching

We kicked off 2020 with a two-day week. Even with the short week, my students fell pretty easily back into classroom routines.

AP Physics 1: Projectile Video Analysis

I like wrapping up linear mechanics with projectiles since its an opportunity to apply pieces of just about everything we’ve learned so far this year. We spent a day on a problem from Michael Lerner representing an orange in free-fall a bunch of different ways. Then, we did some video analysis of tennis balls. In the past, we’ve had to go to a computer lab to do video analysis, so I provided students with a video. This year, since laptop carts are a more practical option, I had each group record their own video. I’m hoping that comparing graphs from different videos will lead to a richer discussion when we have the board meeting next week.

Physics: Cart Catching

To introduce momentum, we did a lab from Scott Lotze, the other physics teacher at Tartan, and had students catch a cart at the bottom of the ramp, then find as many ways as possible to make the cart harder to catch. This lead to an operational definition of momentum and nicely illustrated that both mass and velocity of the cart matter. A few groups tried the plunger carts and noticed they are usually easier to catch, which lead nicely into impulse on Friday.

A hand catching a cart at the bottom of a ramp

Days 68-72: Energy Practical & Pushing Boxes

AP Physics 1: Energy Practical

This week, students worked on applying conservation of energy. We wrapped it up with a lab practical to find the spring constant of a popper toy. To help with what makes a good procedure, I had groups start by writing out the steps they were going to follow on a whiteboard. Then, they traded whiteboards with another group and had to follow the procedure they were given to actually collect data. One group came up with a nice strategy of writing out the equation they’d use in their calculations, then checking off each variable as they added a step to measure it.

Physics: Pushing Boxes

Students spent a lot of time this week on problems applying Newton’s 3rd Law and synthesizing Newton’s Laws, including some great problems originally from Matt Greenwolfe where students draw free-body diagrams and velocity vs. time graphs for boxes pushed across various floors. While there was some great discussion, I think these problems would have been more valuable much earlier in the forces model. In general, I think Newton’s 3rd Law feels like an afterthought in how we approach forces. With some shifts in what we’re doing early in this model, we could better integrate key elements of this model and reduce the need for doing some kind of synthesis at this point in the unit.

Days 63-67: LOL Diagrams & Newton's 3rd Law

AP Physics 1: LOL Diagrams

Students worked on sketching bar charts and LOL diagrams to show energy transfers. I was really pleased with how comfortable students were switching between different systems. I started out the week by having students use a spring scale to pull a cart up different ramps, always raising their cart to the same height above the table. We then sketched force vs. displacement graphs to introduce the idea of work and gravitational potential energy. Getting both simultaneously meant the concepts blurred together for students at first, but that issue got resolved as we did mistakes whiteboarding with energy bar charts and LOL diagrams.

Physics: Newton’s 3rd Law

One of our major tasks this week was developing Newton’s 3rd Law. Students started by predicting how the forces on two colliding carts would compare, then we tested out the collisions. As we tested the collisions, I cued students to notice the relative accelerations of the carts, which I think helped students see the useful thinking in their original predictions. Before we officially stated Newton’s 3rd Law, I borrowed an idea from Mark Schober and had students play with film canisters with magnets inside to test and refine their rule before the whole-class discussion.

Days 58-62: Card Sort & Momentum Bar Charts

This post has ended up a few days late. But I still have yet to miss an intended post on this blog!

Physics: Unbalanced Forces

Students did the classic Newton’s 2nd Law lab with a half-Atwoods machine, then we started fitting net force with the diagrams we’ve been working on. The first set of problems we typically do is just sketching diagrams. This year, we decided to try turning it into a card sort, which I think really helped students who were new to me transfer their knowledge of force diagrams into my classroom, something I’d been thinking about leading into the term. I also pushed using motion maps with acceleration arrows much harder than I have in the past, and one of the results was I got almost no questions this week about which direction the net force should be in.

A set of cards with descriptions of a scenario, free body diagrams, vector addition diagrams, and motion maps

AP Physics 1: Conservation of Momentum

We wrapped up the momentum transfer model (at least for now) by working on conservation of momentum. Students were very excited about Michael Lerner’s watermelon on wheels problem. Aside from being silly, I really like that it pushes students to play with viewing a single scenario with multiple different perspectives. We also did a little bit with momentum bar charts, since they show up in the AP Physics 1 workbook we did a few problems out of, and I found they really helped a lot of my students. I need to make much more use of those bar carts next year.

Days 56 & 57: Finals & Reflecting on Tri 1

This week, we had finals on Monday and Tuesday. Wednesday was scheduled as a professional development day, but an early blizzard meant we had a remote work day for term transition, instead.

AP Physics 1

For the final exam, I had students take a modified practice AP exam. As usual, students did much better on the free response than the multiple choice. I need to give some thought to what shifts might address that. I’m also giving some thought to shifting how I use the formula sheet. Typically, hand out copies of the formula sheet they’ll get on the AP exam pretty early in the year and provide those on all of my assessments. This year, I have more students than usual trying to memorize equations, which tells me they aren’t seeing the formula sheet as a useful tool.

Bigger picture, I’ve been using some of the strategies for improving groupwork that I worked on in Physics last year, and I’m seeing good results, especially in my larger class. This year in general, I’ve been seeing more competitiveness than usual, but it’s been especially pronounced in my smaller class. The small class also has only two girls out of eleven students, and the girls have been vocal that it’s frustrating to often be the only girl in a group. I’ve got some students switching hours and both sections will have a pretty even gender distribution next tri, so I’m hoping that will help shift the tone in my smaller class.


We continued the two-stage final exam, where students complete a standard written final, then do a lab practical in small groups. I saw a lot of mistakes that I think are related to students struggling to differentiate different quantities and to recognize when a letter represents a variable and when it represents a unit. I need to give some thought to how I’ll help students distinguish those concepts moving forward.

My classes have been much quieter than usual this year, both in small group and whole class discussions. Over the course of the trimester, I’ve used some strategies, like giving more opportunity for small group talk before a whole-class discussion, that have helped. Over time, students have gotten more comfortable with each other and I’ve been able to cut back on the pre-discussions, but enough students are switching between hours for next tri that I’m going to go back to those strategies for at least a while as part of re-building the class culture.

Another aspect of the term transition I’m thinking about is the fact that around half of my students next tri will be coming to me from the other physics teacher. While we work very closely together and use the same materials, I consistently find many students do not transfer skills between our classrooms. I feel like I’ve got a good grasp on how to help students transfer skills like collaboration; I treat the start of the trimester the same way I treat the start of the school year and go back to building routines, norms, and a class culture with my students. I can back off quicker than in September, but it’s no less important than in the fall.

Where I feel stuck is with students who struggle to transfer physics skills between classrooms. I periodically hear from students that their class never learned a fundamental skill like drawing free-body diagrams or even entire topics, like balanced forces. Its tricky to coach a kid through that when I haven’t had a chance to build a relationship or get to know their strengths yet, so I tend to end up either helping to the point of giving answers or coming across as harsh about what students “should” know, neither of which is a good start. We’ll be starting tri 2 with unbalanced forces, so I’m giving some thought to how I can navigate these moments more productively. I want to try some open-ended approaches, like sketching a problem scenario I know was used in both courses and asking students very broad questions about what diagrams they might use. I’m also wondering if there are some ways I could involve other group members in these conversations to help them become more productive.

Days 51-55: Final Review

Next week are trimester 1 final exams. In both my courses this week, we wrapped up our last topic and started reviewing for the final.

AP Physics 1: Goal-less Problems

I really like Kelly O’Shea’s goal-less problems, so I decided to try that as a final review. I went through the released free-response problems and took the diagram and prompt from several that could fit with topics we’ve done so far this year. We focused on identifying applicable models, sketching additional diagrams, and reading strategies. Students especially liked a strategy to cross out information in the prompt that is accounted for in the diagram, especially once we started annotating diagrams to get rid of even more text.

An example of annotating a diagram and crossing out text that is accounted for in the diagram

Physics: Units vs. Variables

Students worked on, then whiteboarded a fairly standard final review packet with written problems. One of the biggest things I worked with students on is the difference between a variable and a unit, which has been a recurring challenge this year. For example, in the force of gravity equation, a lot of students are reading “g” as grams, rather than as 10 N/kg. I’ve been working on talking frequently about variables as representing a quantity and quantities as a number with a unit that describe something we can measure or calculate. Going into tri 2, I need to keep thinking about how to help students make sense of when a letter represents a quantity and when it represents a unit that is part of a quantity.

Days 46-50: Center of Mass & Vector Addition Diagrams

AP Physics 1: Momentum & Impulse

This week, we worked on developing the concepts of momentum and center of mass. We wrapped up a video analysis exercise (based on an article in The Physics Teacher by Taylor Kaar, Linda Pollack, Michael Lerner, and Robert Engles) where students track a system of two air pucks attached by a rod. Students made a lot of nice connections between the observed motion and Newton’s Laws, which lead to a lot of great discussion about what objects to include in a system to make sense of the motion. I also got to feel very cool demonstrating center of mass in an explosion with a track balanced on some blocks.

Physics: Vector Addition Diagrams

Students worked on solving problems with vector addition diagrams for balanced forces. We started with an activity I got from Casey Rutherford where students use pipe cleaners to rearrange the vectors on a free-body diagram before moving into problems on paper. A lot of my students struggle with the idea of rearranging the FBD, so starting by literally rearranging the vectors tends to be a useful stepping stone.