We worked on an assortment of pendulum problems this week. The packet starts with some problems that focus on using representations like free-body diagrams and energy bar charts to describe the motion of a pendulum. After that, we shifted to lots of algebra using the equation for the period of a pendulum. With the way our packet is set up, we don’t have students do much thinking or reasoning with the diagrams they sketch. I think with this unit, I’d like to revise our packet to get more emphasis on conceptual thinking about pendulums.
AP Physics 1: Final Projects
Students continued working on their final projects. The projects this year are heavy on calculations to describe scenes in movies or moves in video games. I usually have more projects that involve real-life data collection, but I think this is partly a factor of doing a a shorter project than usual since the AP Physics 1 test was so late this year, so students had less time to brainstorm and to carry out their projects. That said, I am having a lot of fun talking with students about their projects and hearing all the cool thinking they are doing.
We spent most of the week on the pendulum lab exploring the variables that affect the period of a pendulum. This will be our last model-building lab for the year, so it was good to see students figuring out plans for data collection and getting high-quality data with minimal intervention from me. Connecting the data to a mathematical model was still tricky for students, but they worked through the challenging parts to figure out what was going on. They really hated the unit on the slope of their period vs. square root of length graph (I don’t blame them!), but I was able to use that as motivation to try and get a nicer unit by rearranging things so that we had the length divided by a number in m/s2. From there, students were quick to suggest that the slope has something to do with gravity. From there, I showed that the value happened to work out if we put a 2π out front. This approach could use some refining, and I’d especially like to put more of the thinking on students, but students did seem clearer on the significance of the slopes of their lines than in the past.
AP Physics 1: Review
With the AP exam on Thursday, the first three days of this week we focused on review. My students this year really liked Plickers for multiple choice and had some great discussions, when whole class discussions have generally be tough this year. I wonder if I should have pulled out Plickers earlier in the year as a way to get them talking and to build up to some other types of class discussions.
I had a brainstorm for a review activity, that unfortunately came the day of the AP exam, so too late to try. I do a lot of having students start by just looking at the diagram and scenario description, then deciding what models seem useful and sketching some diagrams. It crossed my mind this could lend itself to a card sort, so I put one together with the released free response to date. I haven’t tried it with students, but I think I would start by having students match each prompt to at least one of our models, then give each group a problem to sketch some diagrams and brainstorm what they could figure out.
This week was a little hairy since students were in and out for AP exams. We continued working on using velocity vs. time graphs to quantitatively describe the motion of projectiles. We wrapped up the week with a practical to predict how far from the edge of the table a marble will land. I spent more time than usual working on breaking up the three phases of motion (constant acceleration while the marble is on the ramp, constant velocity while it rolls across the table, and projectile motion once it leaves the table), but it was still pretty challenging for students to connect when to use the measurements they made in their calculations. Based on the conversations I had with students, I think this fits in with a larger pattern I’ve seen this year with students struggling to connect labs to mathematical and graphical representations. As we move into the last few weeks of the school year, I want to make sure I keep thinking about how to support students in seeing the mathematical and graphical representations as meaningful descriptions of something physical.
AP Physics 1: AP Review
We continued reviewing for the AP exam. I didn’t do anything particularly interesting. We started each day doing a few multiple choice questions on Plickers, then moved into working some released free response. For the free response, I let students pick problems to work on based on the topics they want to work on reviewing. With both the multiple choice and the free response, I made sure we spent some time discussing what the problems illustrate about the type of things that tend to show up on the exam, things that tend to show up on the scoring guide, and strategies for approaching the question. A lot of my students have resisted using the formula sheet this year, and it’s been good to see students getting more comfortable referring to it this week and even using formulas to figure out the significance of the slope and area of graphs they are rusty on.
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.
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.
We had Friday off this week. I think staff and students alike were very happy to have a long weekend.
Physics: Popper Hoppers
This week we wrapped up energy. After finishing the bouncy ball evidence-based reasoning from last week, we got out the popper hoppers to use energy to find the spring constant of the toy. We haven’t done as much having students decide what measurements to take as I’d like, so students struggled a little at first with what measurements to take. I showed them a strategy from one of my past AP students wo would write out the equation she was going to use to solve for the target variable, then put check marks next to each of the other variables once she had a step in her procedure that would get her a value for that variable. That was exactly what students needed to get a solid plan for the practical.
AP Physics 1: Unbalanced Torque
This week, we worked on unbalanced torque. We used another Pivot Interactives activity (Disclaimer: I work for Pivot Interactives as a content writer. This activity should be published soon!) since I haven’t had a chance to play with the hands-on equipment we purchased for rotation in fall 2019. I’m trying to be pretty conscious of making explicit connections to unbalanced linear forces, both to make sure students aren’t starting from scratch in their understanding and to embed review of earlier topics. Students are seeing those connections pretty clearly, which is great to see.
I also started a countdown to the AP Physics exam on my whiteboard, and noticed students are more focused when working problems. I think the countdown is adding some sense of urgency to what we are working on.
This week was a little odd since we didn’t have any classes on Tuesday to accommodate state testing. The juniors took the ACT, but the seniors had an asynchronous day. A lot of the seniors really appreciated having a day to follow their own schedule and relax a bit.
Physics: Bouncy Balls
We started an evidence-based reasoning activity to determine what interaction dissipates a bouncy ball’s energy (you can find more details in my article from The Science Teacher). This week we focused on preparing for doing the video analysis by sketching energy bar charts, force diagrams, and motion graphs for if air resistance is responsible for most of the dissipated energy and for if the impact with the table is responsible for most of the dissipated energy. We then used those diagrams to get to some testable predictions about things we can measure with video analysis that will distinguish between those two explanations. Students found this process challenging, but I was really pleased by how they connected other ideas from this course to energy.
AP Physics: Torque
To introduce torque, students set up some meter sticks as levers and looked for a relationship between the force exerted by a hanging mass on the meter stick and the force required to balance the meter stick. After we discussed that lab and took some notes on torque, I showed students a second class lever and asked them to determine if that type of lever showed the same relationship as the first class lever we started with. While I don’t discuss the classes of levers with students, I like that this activity helps emphasize it is the direction of the torque, rather than the direction of the force that is important. This activity was tougher for my students than I expected, I think because I rushed the post-lab discussion after the first class lever, so they weren’t as clear as they needed to be about the relationship we’d found the first day.
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.
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.
This week, we came back from spring break and started trimester 3.
Physics: Energy Bar Charts
This week we focused on drawing energy bar charts. Students have struggled to connect representations, so I tried starting by having students draw the more familiar energy pie charts. Then, we got out the Mathlink cubes to use as a manipulative representing the types of energy (an idea I think I first saw in Scott Hertting’s article in The Physics Teacher). Once students had rearranged the cubes to represent at least two different snapshots, I had them sketch how they arranged the cubes on a bar chart. One thing I was really excited about is as the week progressed, I had some students ask if they could keep using the cubes, which tells me they were a useful tool. I also saw a lot of students sketching energy pie charts to help figure out what the bar charts should look like, which tells me they are connecting the two representations when seeing relationships between representations has been really challenging this year.
AP Physics: Oscillating Springs
Students did a lab to find the equation for the period of a spring, then we dove into some problems. Students did really well with the problems focused on representations and showed a lot of growth from earlier this year on the problems from the College Board’s AP Physics 1 workbook. The workbook problems included a lot of predictions about how various factors would affect the period of a spring, so we used a spring to connect a motion encoder cart to a force sensor on a track so we could change the angle the spring was at, as well as factors students had already tested like mass and amplitude. I also made sure to use this as an opportunity to review some basics on motion graphs since exam day is starting to loom.