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.
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.
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.
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.
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.
We wrapped up Newton’s 2nd Law with some problems combining vector addition diagrams and the 2nd law equation. I’ve been doing a much better job this year of combining vector addition diagrams with motion maps, which is helping students recognize the direction their net force needs to point.
Physics: Force Formulas
Students did labs to find formulas for the force of gravity and spring force. Most of the graphs had pretty good data and students did a nice job on the interpretation. On the force of gravity lab, several groups wrote their slope as 10 N / 1 kg to make it easier to give a “for every” statement during the board meeting, which was great. A lot of groups had some trouble “translating” the equation for their line of best fit into physics; a lot of it is getting tripped up by what a unit represents and separating that from what a variable represents. This is a challenge every year, and I need to keep thinking about how to help students make sense of the differences.
Students used a modified half-atwoods to find a relationship between force and acceleration. The quality of the results varied a lot. I’ve been talking to the AP Chemistry teacher, and we think part of what’s going on is students aren’t often asked to use their data in meaningful ways before they get to physics, so it doesn’t make sense to take the time and attention to collect data carefully. I need to put some thought into how to help students place value on good data collection and build the skills required to collect good data.
After developing Newton’s 2nd Law, we spent some time combining the new equation with vector addition diagrams. Students are starting to buy in to the diagrams as useful thinking tools, which is always a lot of fun to see.
Physics: Free-Body Diagrams
Students have been working on Newton’s 1st Law and drawing free-body diagrams. We have some problems that often lead to great discussion with mistakes whiteboarding, but I’ve been struggling to get students in one of my hours to speak up during whole-class discussions. To help with that, I tried doing a short gallery walk prior to any of the whiteboard presentations this week. Once the whiteboards were ready, I had students visit each board with their group and make notes on their worksheet about potential mistakes they saw or questions they had. During the whole-class discussion, there was a lot less silence and we heard from some students who don’t often speak up, which was exactly what I was hoping for. I think it also helped that I shared those goals with students before we started. When a student joked those goals aren’t going to happen, I assured her I’m very stubborn and am convinced the class can get there.
This was another short week. Parent-teacher conferences were on Thursday night, so Friday was scheduled as a professional development day.
AP Physics 1: Newton’s 3rd Law
This week our focus was on Newton’s 3rd Law. Students predicted which cart would experience a larger force during various collisions, which we then tested using a pair of carts with force sensors and hoop springs. In my grad class this semester, we’ve been doing a lot of talking about the ways language students use can mask meaningful understanding, which got me thinking about how I can make better use of students’ predictions. This year, I tried being very explicit that our task was to find the useful ideas in students’ predictions and to translate those useful ideas into the language physicists use. There was a great moment where a student said “So the force and the result of the force are different things, but we were treating them as the same”, which I couldn’t have planned better.
I also took a page from Brian Frank this week and used some magnetic hooks for an easy setup of a static forces lab practical.
Physics: Newton’s 1st Law
This week was about developing the idea of a force and Newton’s 1st Law using interaction stations and the bowling ball lab. A few students were resistant to actually trying the bowling ball lab this year, rather than actually testing whether what they expected worked, so I had to push some groups to really explore getting the bowling ball moving with a constant speed. Once they got started, however, there was some great discussion.