Forces

Days 92-96: Springs & Impulse

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On Friday last week, I found out our new physics teacher would be starting this week. I went into this year expecting to be doing my role as science content specialist full-time and it has been tricky to juggle that work with my teaching. I’m excited to be able to focus more on my role, but it is hard to be getting ready to leave students I’ve been with for a while. The new teacher shadowed me this week so he could start getting to know the students and the curriculum. We will then be co-teaching until the trimester ends on March 10. Trimester 3, he will take over Physics completely. I’ll still be in AP Physics 1 on occasion up through the AP exam since this is our new teacher’s first time doing AP and it’s a lot to get the hang of in a short amount of time!

AP Physics: Springs

Students conducted an experiment to find factors that affect the period of a spring. The data was kind of rough, mostly because they were having trouble getting the springs to oscillate nicely. We still had enough good data in the class that we were able to figure out all the things we needed to. On both this and the pendulum lab, I was really pleased with how students used the intercept of their graph to figure out they needed to linearize. After the lab, we worked on some problems with representations for simple harmonic motion. It was a lot of fun to see students putting together forces, energy, and motion graphs to make sense of simple harmonic motion and they made a lot of great connections.

Physics: Impulse

This year, we tried a new sequence for momentum where we started with conservation of momentum since looking at a system that includes both objects in a collision is a really strong motivator to learn momentum. This week, we did Newton’s 3rd Law and used that combined with Newton’s 2nd Law to derive impulse and start thinking about individual objects. This was a tough transition for a lot of students to make and I’m wondering about ways we could make it smoother in the future. One thought is we don’t emphasize system choice in Physics, but that is pretty key to thinking about impulse. I’m not sure what to do with this thought yet, but definetly want to keep it in mind.

Days 73-76: Where Does the Energy Go & Math Sensemaking

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AP Physics: Where Does the Energy Go

This week, students started working on an activity to figure out what interaction causes energy to dissipate as a bouncy ball bounces (I wrote this up for The Science Teacher a few years ago). After observing a bouncy ball, students agreed that some combination of the impact with the table and the air resistance on the bouncy ball are responsible for the energy dissipating, so now their task is to figure out which it is. I spend a lot of time priming students for what evidence might be useful and we started late in the week, so we mostly focused on making one set of energy bar charts for if only the impact dissipates energy and one set for if only the air resistance dissipates energy using five key points along the bouncy ball’s motion (right as it’s released, right as it reaches the table, right as it leaves the table, at the top of the first bounce, and right as it reaches the table a second time). I forgot to get a picture, but one group did a cool thing where they labeled which interaction was happening between each of their bar charts to help keep track of when the dissipated energy should show up. We then had some good discussion about what these energy bar charts tell us we will actually observe in the lab.

Physics: Math Sensemaking

This week felt a little goofy. The other physics teacher and I are doing the same activities on as close the same day as we can so that we can plan together (a key survival tactic when both of us are also doing what are supposed to be full-time jobs outside the classroom!). He is out this week, so we used several Pivot Interactives activities to wrap up forces and introduce momentum (full disclosure: I work for Pivot writing activities). As I worked with students, two big things that aren’t directly tied to the science content ended up at the front of my mind. First, students told me their biggest frustration with the Pivot activities is they had to measure carefully to get the autograded questions correct. I think this fits with where students believe that physics knowledge comes from. When students see experiments, observations, and measurements as where physics knowledge comes from, I find that students tend to measure more carefully because they see a purpose to having good-quality measurements. Combined with some other things I’ve observed about my students, I think many of them see me as the primary source of physics knowledge in the room, so why should it matter whether they measure carefully?

Second, I saw a lot of evidence that students are not attaching physical meaning to their measurements. This was most apparent to me in an activity where students used Newton’s 2nd Law to determine the mass of an unknown object. Students were able to measure the net force on a system that included two gliders and the mystery object as well as make measurements to determine the acceleration of the system. Once they calculated the total mass of the system, a lot of students really struggled with how to use the given mass of the gliders to figure out the mass of the mystery object. This made me think of the work some of my grad school classmates and professors have been doing around blended sensemaking in science (here’s a taste), which is a term for simultaneously doing sensemaking in science and in math. Recognizing they needed to subtract the mass of the two gliders from the total mass required students to recognize what the mass they had calculated represented, how the given mass of the gliders relates to the mass they had calculated, and what the operation of subtraction represents in this context. Doing all of that can be some pretty tricky blended sensemaking! Realizing how much my students are struggling with this is helping me make sense of some of the other struggles I’m seeing in my class right now. I’m not sure what my fix is yet, but I definitely want to keep thinking about how to support students in attaching meaning to numbers and doing blended sensemaking.

Days 68-72: Energy & Forces

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This was another week that was a little messy. I had a sub Wednesday through Friday so I could present some of my doctoral research at the ASTE conference. On top of that, we had an ice storm early Wednesday morning that resulted in a late start, so two of my classes didn’t meet

AP Physics 1: Energy

This week was all about applying our model of energy transfer. We had some great discussions before I left where students were navigating how different systems affect the problem. We also did some TIPERs problems where some common preconceptions came out. The last few years, I’ve been working on being more intentional about making sure we discuss what’s correct about those preconceptions and whether there are other questions those ideas are the correct answer to. My students this year have been really receptive to those conversations, which makes for fun discussions and seems to help kids feel comfortable sharing ideas. Once I left, students worked on an energy lab practical in Pivot Interactives and some energy problems from the College Board’s AP Physics 1 workbook. My students were a little nervous about doing those problems without a teacher who knows the content in the room, but I’m betting they will make some good progress with peer conversations.

Physics: Unbalanced Forces

Students started working problems using unbalanced forces. My students and I are getting more comfortable with each other, which is leading to the discussions getting better. That’s helped me make the connection that the reason some of my students have been struggling with the direction of some forces is they don’t have a great conceptual understanding of the interactions involved in some forces, especially the normal force. I made sure we spent some time reinforcing those ideas by doing some things like using the matter model for normal force and a pair of hairbrushes for friction. My go-to move is to place those on a board at different angles to help students get a visual and tactile hook to make sense of what direction the normal and friction forces should go, which seemed to help a lot of students. We also spent some time looking at how the normal force an elevator passenger experiences connects to the acceleration of the elevator. Once I left, they did an unbalanced forces lab practical in Pivot Interactives.

Days 64-67: Kinetic Energy & Newton’s 2nd Law

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This week was a little goofy. Tuesday was our first day back from break, then a big winter storm meant we had to close schools on Wednesday. We used up our regular snowdays in December, so Wednesday was an emergency e-learning day, which means students completed asynchronous assignments.

AP Physics 1: Kinetic Energy

Our first task back from break was to find the relationship between velocity and kinetic energy. I waffle every year whether to do this with tracks and probeware, which as the advantage of being firmly rooted in the real world for students, or use Pivot Interactives, which has the advantage of measurements that are easier to make. With the weather forecast, I opted for Pivot. I had students complete the first section that takes them through making measurements and modeling the energy transfers with energy bar charts individually, then complete the remaining sections in groups. It’s been a little while since we linearized a graph or developed a mathematical model from data, but I was really pleased with how they did.

Physics: Newton’s 2nd Law

Our big goal this week as a paradigm lab for Newton’s 2nd Law. In some conversations last year, Kelly O’Shea suggested using carts on ramps as an alternative to the more standard modified Atwoods machine. Students used a force sensor to measure how much force it took to hold the cart in place. Next, we used some vector addition diagrams to reason out the force they’d measured is the same as the net force when the cart is released. Students used the motion encoder carts to determine the acceleration, then changed the angle of the ramp and repeated their measurements. I really like that this is conceptually much simpler than the modified Atwood, so students can focus on making sense of the data, and this approach makes a really clear conceptual link between balanced forces and unbalanced forces. For the e-learning day, we had students do some reasoning with vector addition diagrams of balanced forces to help review those skills to support the lab.

Days 57-60: Impulse & Force Practicals

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We had a snow day on Thursday, so got a surprise short week. Plus some beautiful fresh snow to enjoy this weekend!

AP Physics 1: Impulse

This week, we wrapped up impulse. I tried a new sequence this year where I started with conservation of momentum, then shifted into impulse and using momentum for single objects. I feel like my approach could still use some refinement, but overall I felt like the storyline made a lot of sense. My students found it a little tricky this week when we did some problems where they had to switch between different systems when thinking about the same scenario, which tells me that’s something I need to make sure we keep working on. We are starting energy next, which is a good opportunity to keep working on the idea of systems.

Physics: Force Practicals

This week we did a lot of work doing problems with balanced forces. Students were in a lot of different places on their math skills, but were able to get the problems down. We finished the week with two different lab practicals. For one, students had to find the mass of a cart on an angled ramp. For the other, students had to find the mass of a bag hanging from two spring scales. I set up several stations for this lab practical on my whiteboard using hooked magnets, and I was excited to see some students sketch diagrams on the whiteboard right by their station. On both practicals, I was really pleased by how quick students were to check their answers on the scale I had out. Last year, it was really tough to get students to see the connection between the physical world and the math we were doing, and one way that showed up is a lot of students were not invested in checking their answers on lab practicals. I think sketching diagrams on the whiteboard next to the practical also helped cement the links between the representations we’ve been using and the physical scenario.

Days 53-56: Impulse & Vector Addition Diagrams

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After a staff development day on Monday, we started trimester 2 this week. This trimester, I’m adding two sections of Physics to my teaching load.

AP Physics 1: Impulse

This week we spent a lot of time working with impulse. Near the end of last trimester, it clicked for me that my students have been very quick to grasp conceptual thinking and can do great on problems like those from TIPERs, but need more practice than I’ve been giving them on calculations. To help with that, we did a lot of whiteboarding calculations this week and did a lot of work making sure everyone grasped the connections between momentum bar charts, force vs. time graphs, and the equations we’re working with. This was the kind of week where I really saw the value of frequently changing groups; since students were with different people almost every day, they were pushed to do a lot of explaining their thinking to each other rather than falling into the shorthand that can happen when you are working with the same people consistently.

Physics: Vector Addition Diagrams
This week, we did a lot of work translating between free body diagrams and vector addition diagrams. We did an activity I love from Casey Rutherford where students make arrows out of pipe cleaners over the FBD, then rearrange them to make the VAD. Students had done some practice with this at the end of last trimester, so things went pretty smoothly, but it was helpful for me to start getting a feel for what they have down and what they need more work on before we start adding in calculations.

One thing that felt a little tricky this week has been figuring out how to establish the classroom culture that I want. Usually, around half of our students stay in the same hour for physics when a new trimester starts, so I’ve gotten used to have to do some culture-building at the start of a trimester for the students who are new to the hour, especially if they had the other physics teacher, but I have a foundation to build on thanks to the students who’ve been in that hour since September. What’s been tricky this week is there is still a core of students who have been with each other in this space doing physics together since September, but they were with a different teacher who has some differences in the kind of culture he builds, so I’m asking students to unlearn some things that have been established as part of physics class for the majority. I’m trying to be really explicit about why I’m doing things the way I am and leaning much harder into culture-building strategies than I normally do at this point in the year, but I think we’ll get here.

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

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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

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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 32-36: Using Newton’s 2nd Law

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This week, our big focus was on using Newton’s 2nd Law. Students were very successful at using vector-addition diagrams with unbalanced forces and did a nice job playing around with different systems on problems involving Atwood’s machines. We wrapped up the week with an extremely open-ended lab practical. I tasked students with finding the mass of a dynamics cart with a force sensor attached and left it at that. I did ask students to get my okay before they started data collection so I could make sure every group was on a good track. I was really pleased that groups ended up using several different approaches. Some did something similar to our model-building lab with a half-Atwood’s machine, some set their track at an angle to apply a force to their cart, and some manually pulled the cart. On Monday, I want to take a few minutes to make sure we talk about the different approaches, including the different ways uncertainty showed up in each.

Days 27-31: Balanced Force Practical & Newton’s 2nd Law Model-Building

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This week we wrapped up balanced forces with a practical. I used some magnetic hooks to attach spring scales to the whiteboard and let students measure the forces and any angles they wanted. Even though I only had two setups and five groups, different groups ended up taking different approaches, which was great for students to see in some discussion after the practical. We also had some good discussion about uncertainty when we measured the actual mass and students were initially disappointed with how far their calculations were off before, which lead to the realization they’d actually been pretty on target!

After the practical, we started Newton’s 2nd Law with a paradigm lab using the standard modified Atwood’s machine. There was some messiness in the value of the slope that students got, which is pretty typical from when I’ve done this lab. One of these days I’ll figure out how to coach students to really high-quality results! Students did really well at translating the equations for their line of best fit into something that had units and variables that matched the experiment and did a nice job in the board meeting making sense of their slope and intercept.