# Days 82-86: Projectile Calculations & Momentum Conservation

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 41-45: Conservation of Momentum & Newton’s 3rd Law

This week we developed conservation of momentum. Previously, I started with impulse and momentum of single objects, then built up to conservation in systems. I’ve never been thrilled with my storyline, so this year I am trying putting conservation of momentum first, then we will work toward impulse. Once we’d done a lab with some collisions and talked about momentum bar charts, we did Kelly O’Shea’s multiple representations of momentum card sort to incorporate mathematical representations. The card sort really helped my students feel confident with the bar charts and to make sense of the mathematical representations.

We ended the week with Newton’s 3rd Law. I feel like this law fits better with my momentum storyline than my forces one, so this was their first introduction to the 3rd Law. I had students predict how the forces would compare on two carts for a variety of collisions, then we actually tested the collisions out using some force sensors with hoop springs. This is a very rare time that I ask students to make a prediction that I think they are likely to have wrong, so was very intentional in talking to students about my goal of pulling out their existing ideas so we could contrast with the accepted physics. I also made sure we talked about what useful thinking lead them to the incorrect predictions and what physics their predictions showed they know. There was a fantastic moment partway through where a student articulated that both the forces we were measuring came from the same interaction, so it made sense for the size of the force to be the same. She also realized the cart she expected to experience a bigger force did have a bigger change in motion, which was a great opportunity to validate the thinking that lead to that prediction. It was a great note to end the week on.

# Days 37-40: Unbalanced Forces

This week was a little funny because we had Tuesday off for elections.

On Monday, I gave a quiz over unbalanced forces that didn’t go as well as I’d hoped. The big thing students seemed to struggle with was sketching and using free-body diagrams and vector addition diagrams. I decided to put off starting momentum to spend a little extra time working on force diagrams. We started with a card sort with unbalanced force diagrams. Including the motion maps gave me a chance to emphasize the net force is in the same direction as the acceleration, which I hadn’t done a great job of before. This card sort also includes two sets of similar scenarios, which lead to some good conversation comparing and contrasting the similar scenarios. After the card sort, one student told me that she has found card sorts in general to be a really useful tool in helping to visualize what diagrams should look like. I realized one of the benefits of card sorts is they students the visual they are after when they ask me to do example problems on the board, but kept the bulk of the sensemaking on students. We have a lot of card sorts made for our physics courses, but I don’t use them consistently in AP in an effort to keep to a fast-moving pace. This week was a good reminder that it is worth it to make time for card sorts.

After the card sort, we moved into doing some problems, both calculations and conceptual, and students were much more confident and doing much better than earlier in the week.

# Days 157-161: Pendulums & AP Review

Physics: Pendulums

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.

# Days 128-132: Energy Conservation & Rotational Kinematics

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 100-104: Momentum Conservation & Projectile Practical

Physics: Momentum Conservation

This week we did a lot of work on conservation of momentum. We started with using photogates to measure the velocity of carts before and after a collision to reinforce the idea that momentum is transferred, then we did a momentum representations card sort from Kelly O’Shea before students tried some problems on their own. One thing I noticed is a lot of students are still struggling with what momentum is. I think a lot of students were having trouble taking in new ideas during distance learning, and are now struggling to build on those ideas. Students had a lot of great conversations during the card sort, and it was a lot of fun to see how they applied that thinking to the problems later in the week.

AP Physics 1: Projectile Practical

This week we wrapped up projectile motion. Students did a projectile practical where they predicted where a marble would hit the floor. I like to take advantage of the different masses of marbles I have and ask students to predict how the landing spot would change if they switched to a lighter marble, and students consistently nailed it. One fun thing has been seeing students use multiple different models to think about projectiles and the confidence I’m starting to see from more students.

# Days 75-79: Values and Beliefs & Elastic Potential Energy

This week has felt a little weird. Coming back from break, we’d gotten some messages to be ready to shift to virtual learning and all week the number of students and staff out went up, so everyone felt like we were in limbo. Near the end of my teaching day today, we got word that next week will be remote.

Physics: Values & Beliefs About Physics Learning

We started this week with a version of the values and beliefs lesson from Kelly O’Shea. There wasn’t as much discussion within groups as I was hoping (and it probably didn’t help that I was giving groups more space than usual to try and reduce my COVID exposure), but students had some great insights and really interesting things to say on the individual reflections I had them complete. One thing I felt like was missing in how I implemented this was some conversations about the costs and benefits of different views of physics and physics learning. One of the last things I had students do in their groups was pick some values or beliefs they think we should aspire to, and a lot of groups said we should aspire to do a better job of valuing memorizing facts and equations. I wonder if giving more space to why certain values and beliefs are or are not given a space in a particular classroom would have helped with some conversation about why they see memorizing as important and whether that is compatible with our classroom.

After two days of that, we spent the rest of the week on some problems about pushing cardboard boxes based on problems in Matt Greenwolfe’s More Models in Modeling materials. My goal was to refresh students on velocity vs. time graphs and free-body diagrams before we dive into momentum. There was a lot of great discussion, with lots of animated arguments. I was also really pleased at how often I could have students simply add a diagram, such as a system schema, to identify and fix their mistakes. I still need to work on how to facilitate a good whole class discussion with these problems, but I think part of the issue is I approach these problems with what I call consensus-building discussions, where I have every group whiteboard the same problem, then we try to resolve differences, but I don’t do this type of discussion very often so students don’t have much practice with it.

AP Physics 1: Energy

This week, we focused on going from LOL diagrams to doing calculations with conservation of energy. We started by doing a lab to find the equation for spring potential energy, which gives us all of the major energy types, then did a card sort that included equations based on just the types of energy and equations based on measurable quantities like velocity, mass, and height. The card sort made for a very nice bridge between the two types of mathematical representations.

# Days 62-71: Unbalanced Forces & LOL Diagrams

I think last week is the first time I missed a post on this blog. The end of my grad school semester plus the usual challenges of the Thanksgiving to winter break stretch got the best of me.

Physics: Unbalanced Forces

Last week, we did a paradigm lab for unbalanced forces. I was really dreading the classic half-Atwood machine, so tried a lab Kelly O’Shea suggested. We set up a ramp, then used a string to connect a cart to a force sensor. Next, I cut the string and students observed that the cart accelerated down the ramp. Students were able to reason out that the tension in the string before it was cut must match how unbalanced the forces on the cart are after the string is cut. Students also were quick to recognize that we could change the tension in the string by changing the angle of the ramp. Students then went and collected data to find a relationship between the size of the unbalanced force and the acceleration of the cart. Compared to the half-Atwood, students had a much clearer conceptual understanding of the lab and the data was much cleaner, so I will be sticking with this approach.

This week, we introduced problems by starting with a card sort where students matched a situation to the motion map, free-body diagram, and vector addition diagram. The acceleration arrows on the motion maps seemed to help students with thinking about the direction of the net force, though a lot of students needed some prompting to use the motion maps. I think that is because they haven’t been a very meaningful sensemaking tool in my class before now. If I want students to be ready to use them with unbalanced forces, I need to give some thought to how I’m going to push students to make meaning from motion maps when they are first introduced.

AP Physics 1: Conservation of Momentum & LOL Diagrams

Last week, we worked on conservation of momentum. I introduced momentum bar charts so we could do some problems from the College Board’s AP Physics 1 workbook. They seemed to really help students, so I wish I’d introduced them much earlier. Students ended up not making much connection between the problems we’d done earlier and the momentum bar charts, so I think I needed to introduce the bar charts right off the bat. The quiz didn’t go as well as I would have liked, but next week’s quiz will include a retake. I’m thinking about what I want to build into class next week as a way to address the gaps I saw on the quiz.

This week, we’ve been focused on energy bar charts and LOL diagrams. We did a lab I’ve done in the past where students raise a cart to the same height above the table using ramps of different angles to see the force vs. distance graph always has the same area. After that, I defined the major forms of energy we’ll be dealing with and students practiced drawing energy bar charts, including for situations where they switch between systems. These are coming really easily to my students and we had some great discussions using mistakes whiteboarding on some bar chart problems. The big challenge will be helping my students revisit these ideas after break.

# Days 25-29: Mistakes Whiteboarding & Free-Body Diagrams

Physics: Mistakes Whiteboarding

This week we did a lot of practicing with constant acceleration diagrams. The highlight was doing mistakes whiteboarding. Based on a recent conversation with Kelly O’Shea, I was much more explicit that the role of the group presenting is merely to facilitate the discussion while the role of the rest of us is to help them get to the right answer. In two of my classes, this seemed to be really freeing for a lot of groups as they presented, and lots of students were quick to ask their peers to justify changes to the whiteboard when they were presenting. There was also some fantastic back and forth where the students who weren’t presenting disagreed about what to change on a whiteboard and had exactly the kind of discussion I’m after with mistakes whiteboarding. In my third section, the discussion was still pretty rough, so I need to give more thought to how I can support them in having deeper student-to-student discussions.

AP Physics 1: Free-Body Diagrams

This week we focused on drawing system schema and free-body diagrams. I was reminded how much I love framing forces in terms of interactions and the discussion that comes out of even the very basic free-body diagram problem set in the Modeling Instruction materials. I love that on a problem about a skater sliding across frictionless ice at a constant velocity, I get to hear students internalize Newton’s 1st Law as they wrestle with what interaction could be giving the skater a forward force. This year, my students also got into Newton’s 3rd Law during the discussion as one student pointed out the ice is pushed downward by the skater’s foot, so the class wrestled with how that impacts the normal force before agreeing that same interaction pushes the skater up and the ice down. We also did Kelly O’Shea’s force diagrams card sort, which I use as students’ first introduction to vector addition diagrams. I was really pleased by how easily they connected the vector addition diagrams to the free-body diagrams and by how they started contrasting balanced and unbalanced force scenarios with minimal input from me.

This year has felt unusually draining so far, but my students are doing some great work in my class and reminding me why this job is worth it.

# Days 103-106: Kirchoff’s Laws & Energy Card Sort

AP Physics 1: Kirchoff’s Laws

Students worked on developing Kirchoff’s Laws this week. We started with PhET’s circuit construction kit, then got out the power supplies and resistors. Some groups had trouble recognizing the simulation and the physical lab as addressing the same concepts, but explicitly asking groups how their results compared seemed to help students make the connections. There was also some good discussion about why the results in the physical lab didn’t match the simulation exactly. A thermal photo showed some heat at the alligator clips, which lead to some conversation about whether the wires we were using were ideal.

Physics: Energy Transfer Card Sort

This week we worked on starting energy conservation problems. To help the transition from bar charts to problems, I turned some problems Kelly O’Shea and Mark Schober wrote for the New Visions physics curriculum into a card sort. Seeing cards with two versions of the conservation of energy equation seemed to help a lot of students see how to build equations from the bar charts, which made the problems much smoother than in the past.