Motion

Days 82-86: Projectile Calculations & Momentum Conservation

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AP Physics: Projectile Calculations

This week we worked on wrapping up projectile motion by focusing on calculations. Students were a little rusty on using velocity vs. time graphs to set up equations since we haven’t practiced it in a while, but I was very pleased with how quickly they got back into the groove with those skills. We ended the week with the classic projectile practical where students predict how far from the table a marble will land and it was great to not only see students nail it, but feel good about nailing it. Once students succeeded, I gave them a lighter marble and asked them to predict where it would land relative to their original, heavy marble, which lead to some great conversation.

Physics: Momentum Conservation

This week we started transitioning to quantitative momentum conservation, including a lab where students did a series of collisions and comparing the total momentum before and after the collision. It’s always tricky for students to make sense of the graphs produced by the photogates, so this year when we had some extra time the day before, I tried doing a few collisions and projecting the results. Then, I had students get into groups and whiteboard their interpretation of which velocity was which. That exercise paid off and the lab went the smoothest it ever has for me as students were much more confident at reading the graphs with the skill to back it up! We ended the week with Kelly O’Shea’s momentum card sort, and there was a really great moment where a student was explaining to me how he worked backwards to make a velocity vs. time graph from an equation by solving for the unknown velocity. Given how much I see students struggling with math reasoning, it was a lot of fun to see a student feeling confident enough to make sense of the equation in that way, which I don’t think would have happened if we’d gone straight to problems.

Days 77-81: Projectile Graphs & Cart Explosions

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AP Physics 1: Projectile Graphs

This week was all about velocity vs. time graphs for projectiles. We started with some video analysis of videos students had recorded to see what the graphs looked like. Students did a really nice job during the board meeting of connecting the graphs to other key ideas, like the forces acting on the projectiles. I showed students the three views of a projectile video from Pivot Interactives that shows a side view where the full 2D motion is visible, a top view where only the horizontal motion is visible, and a front view where only the vertical motion is visible. Even though we didn’t do an activity with the videos, students referred back to it when making sense of why we had two different velocity vs. time graphs. It was also fun to see more students making connections to derivatives now that they are further along in calculus than when we did motion in September.

Physics: Cart Explosions

Students did the cart explosion lab from the Modeling Instruction materials. They easily picked up on the pattern in the data, but I never feel like the connection between their data and the idea of conservation of momentum is as clear as I ‘d like. I think one trick is momentum doesn’t have a very good conceptual definition and mathematical reasoning has been challenging so far. Once we started working on momentum bar charts, students were doing really well with them and doing a lot of connecting the bar charts to what they’d observed in the lab, which was great!

Days 10-14: Building CAPM

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This week, students did a lab with ramps to start building the constant acceleration of a particle model. Students used Vernier Video Analysis to get their graphs, and I really love how the video analysis tracks set up motion maps for constant acceleration. Students seemed to feel pretty good about some of the math-y skills in this lab, including linearization and “translating” their line of best fit into a version that has variables that match the experiment and units on the slope and intercept. We then did some mistakes whiteboarding with problems translating between different representations of constant acceleration, which my students continued to do fantastic with.

One thing I think is worth thinking about it it feels like because this is our first experience with linearization, the later days of this lab feel very focused on the math. Then, it feels like we set the heavy math aside while working on translating between representations, only to circle back once we are ready to start doing problems. I wonder if there is a way to structure the constant acceleration unit differently to make it feel more coherent. We have the Vernier motion encoder carts, so I wonder if one option could be to start by having students more or less play with carts on ramps to focus on the shape of graphs, then work on translating representations. Then once students are solid on the representations, do the more standard ramp lab to bring in mathematical representations.

Days 5-9: Deploying CVPM

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This week was all about using the constant velocity of a particle model. We started with some problems translating between different representations that we went over using mistakes whiteboarding. Last year, I had some classes where it helped to do a gallery walk before the whole class discussion, so I decided to try that from the start this year. This class did a great job with the gallery walk and every student was able to say something about every whiteboard. They also did a great job during the whole class discussion. There was one whiteboard that sparked some great student-to-student talk where I could hear students getting a better understanding of motion maps as they talked.

We wrapped up the week by predicting where two buggies would collide. I told students there was a range of possible approaches, and one group took that as a challenge to find as many different approaches as they could. A homecoming pepfest on Friday meant we ran short on time to have students share how they approached the practical, but I want to make sure and revisit that next week.

I also set aside some time this week to work on good collaboration. That is something I was not very consistent about last year, and I think it contributed to how much some students struggled in groups. We spent some time discussing the different kinds of contributions that were useful this week to ensure students are seeing a variety of ways they can be good at physics. Next well, I’m planning to introduce group roles.

Days 1-4: Buggy Lab

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I’d expected to give this blog a break for this year, but a last-minute resignation meant I’m back in the classroom for at least part of this year. At the moment, I’m just teaching one section of AP Physics 1.

Like usual, I started with the buggy lab. Like I’ve been doing for a few years, on day 1, I asked students to make a graph that models the motion of their buggy with almost no other instruction, then had a board meeting that focused on what we would need to change in order to set ourselves up better to compare results across groups. Then, the next day, we repeated the lab with some agreements about things like units and graph axes so we could compare results. Every group collected one set of data with a full-speed buggy moving forward from zero and one set of data with a variation I assigned them. In the board meeting, students easily recognized the slope represented he speed and the intercept represented the starting position.

In the past, I’ve insisted students use time as the independent variable and collect data at even time intervals, but I skipped that this year. I ended up regretting it because the ways students measure when time is the independent variable lead so nicely into a motion map, so that could make next week trickier since only a few students have had that experience.

Days 15-19: Applying CAPM

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This week was all about applying the constant acceleration of a particle model. Students worked some problems, including a few from the AP Physics 1 workbook. I had more students than usual try to use the formula sheet, but they pretty quickly shifted to relying on velocity vs. time graphs to solve problems, which I am all for. When we did some mistakes whiteboarding, I tried to keep the focus on setting up the problem by asking students to make a mistake in the velocity vs. time graph, annotation, or setting up an equation. I posted my solutions for the problems on Schoology after class so students could check their algebra later.

The highlight of the week was the catch the loot practical, where students figured out where to start a marble on a ramp so that it would land in a buggy driving by. This year’s students were much more invested than last year’s in getting a successful result, which makes me think they are more comfortable with hands-on work than my students at this point last year.

Days 147-151: Free Fall Practicals & AP Review

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Physics: Projectile Practicals

It’s been tough for students to make connections between labs, diagrams, and mathematical representations this year, so I was nervous about the shift this week from sketching diagrams for projectile motion to doing problems. I had a brainstorm on my way to work for scaffolding that transition that worked out really well. First, we did a lab practical where each group got a strip of clear acrylic and a random time. They were tasked with calculating how far apart they should place pieces of tape so they could get a photogate to read their time. That meant students only had to think about the vertical motion, which seemed to help with connecting measurements, diagrams, and mathematical representations.

The next day, I wanted them to think about motion in both directions, but keep the distinction between those two directions very concrete. We tried a lab practical I’ve seen where each group got a random distance for a constant speed buggy to travel, then had to calculate where to drop a marble from so it would land in the buggy. The two separate objects seemed to help students wrap their heads around what we mean by the vertical motion and what we mean by the horizontal motion and why the time must be the same for both.

At this point, we talked a little about how thinking about the motion of the buggy and the motion of the falling marble simultaneously was similar to thinking about the motion of a projectile. Students seemed to make that connection really nicely. One benefit I hadn’t thought about in advance is they also seemed more confident starting the problems, having already had multiple, tangible successes with this kind of thinking. This seems like it could be an argument for putting lab practicals or similar experiences early in a unit, rather than only toward the end where we tend to use them.

AP Physics 1: AP Review

We wrapped up angular momentum and started reviewing for the AP exam. We spent some time on model summaries, where students revisited the diagrams and equations central to each major model we’ve used this year. The next day, I handed out the 2021 free response and we took some time to just read the problems and talk about things the students noticed. Next, I gave students the scoring guide and we made some observations. Finally, I handed out the student samples that are publicly available to make more observations. This lead to some good discussion about what the readers are looking for as well as some good conversation about strategy, like how to make use of diagrams or the importance of taking the time to break apart the text.

Days 142-146: Projectile Video Analysis & Angular Momentum

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Physics: Projectile Video Analysis

Students used Vernier Video Analysis to get velocity vs. time and position vs. time graphs for a projectile. I saw some students including their throw or after the projectile landed in their video analysis, which makes sense since I’ve seen students struggling more than in the past with recognizing what is the most relevant part of an object’s motion. I think that probably could have been addressed with spending a little more time on some pre-lab discussion. It was a lot of fun to hear their small-group discussions making sense of the graphs once I had them draw a free-body diagram and they recognized why the graphs looked the way they did.

AP Physics 1: Angular Momentum
We wrapped up unbalanced torque and rushed through angular momentum. Students started an activity in Pivot Interactives, but were moving through it more slowly than I’d hoped, so I ended up doing a lecture on angular momentum. It’s not my preferred approach, but the clock is ticking for AP exam day! Students seemed to get the concept during the lecture. I did a lot of emphasizing the parallels to linear momentum, which seemed to help. We’ll be doing some problems and whiteboarding next week to wrap up angular momentum, which will be a good opportunity for me to check how clear their understanding is.

Days 128-132: Energy Conservation & Rotational Kinematics

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Physics: Energy Conservation

This week we worked on making the transition to setting up problems for conservation of energy. Before doing problems, we did a card sort where students matched scenarios to energy bar charts, conservation of energy equations using only energy forms, and conservation of energy equations where the formulas were substituted for the energy forms. This seemed to really help students connect the two different versions of the conservation of energy equations and were something I was able to refer back to when students were working on calculations on paper. Whenever students refer back to an activity as we tackle the next challenge, that is a sign to me that the activity was worthwhile.

AP Physics 1: Rotational Kinematics

This week we worked through rotational kinematics. We started with an activity on Pivot Interactives where students analyzed the motion of some dots on a spinning wheel (disclaimer: I write activities for Pivot Interactives. This one should be published soon!). Students very quickly made connections to linear kinematics, which was exactly what I was hoping for. From there, we did a card sort with motion graphs for rotational kinematics where students again saw the connections to linear kinematics really clearly. I’d printed and cut this card sort back in February 2020 with the intention of using it that spring, so it was exciting to finally pull it out of the cabinet! One of the advantages of students making those connections is these activities served as a really natural review, which I try to incorporate into these last topics as the countdown to the AP exam begins.

Days 123-127: Kinetic Energy & Centripetal Force

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Physics: Kinetic Energy

The biggest task this week was a lab to determine the equation for kinetic energy. On some recent labs, students have struggled to get good data. I think part of the issue is many don’t buy into the idea that knowledge should come from the labs they do, so they don’t invest the effort or attention into getting good data, which makes it hard to see how it leads to physics concepts or equations and becomes a self-reinforcing cycle I wanted to interrupt with this lab. We talked a little about what I observed and my hypothesis, then I re-did the gravitational potential energy lab as a demo and made a point of discussing the things I was doing to get good measurements and check the quality of my data as I went. When we were getting ready to whiteboard, I also checked in with groups to make sure they had quantities on the correct axis and were seeing that they needed to linearize. The result was data that really nicely showed the quadratic relationship between kinetic energy and velocity and most graphs even had slopes very close to half the mass of the carts students used! A lot of students were really proud of their results, which was great to see and I’m hoping will encourage them to continue those good data collection practices.

AP Physics 1: Centripetal Force

I like to ignore the College Board’s recommendation to do centripetal force as unit 3 because it is such a nice opportunity for built-in review of a lot of ideas about forces. We started by spinning some rubber stoppers on strings to talk qualitatively about how we could change the force in the string before moving over to Pivot Interactives to collect quantitative data (disclaimer: I am a content writer for Pivot Interactives). Next, we used an activity I originally got from Lucas Walker using exoplanet data to find the law of universal gravitation. Students are making the connections I want them to, but I can tell they are starting to feel some fatigue. I typically rely a lot on Pivot Interactives for this topic since we don’t have much equipment, but students got pretty into the brief hands-on activities we did this week, so I think I should make sure to keep working those in to help my students stay engaged these next few weeks.