November 10, 2021
Physics Teacher Marta Stoeckel describes how she introduces her students to Newton's 1st law using bowling balls and a simulation in Pivot Interactives to help them build confidence in the idea that balanced forces produce constant velocity motion.
Last week, we wrapped up kinematics in my classes. One thing that was very clear is my students are struggling more than usual to connect what happens in the lab to other modalities, like written problems, as well as to do sensemaking in the lab. This means that as a teacher, I need to give some thought to how I will help students bridge those gaps. As we started forces this week, I spent a lot of time thinking about how I introduced each activity to ensure students saw the connections as well as how to link what we were doing in the lab to more abstract representations.
We started with an activity adapted from Frank Noschese’s version of mallet ball, where students tap a bowling ball with a rubber mallet to produce various changes in the bowling ball’s motion. In the past, I’ve had the occasional group who leaves their bowling ball on the table and just record what they think they’d need to do for each type of motion. This year, when I was introducing the activity I took some time to talk about the difference between prediction and observation, as well as the purpose each can serve in the classroom, then emphasized that this activity is about observation, so they needed to try each task even if they were certain what they would need to do. Every single group ended up trying each type of motion with their bowling ball, which tells me this was a worthwhile discussion.
My students have also struggled to connect representations like motion maps and graphs to things they can concretely observe. I have students make motion maps as part of this activity to lay the foundation for connecting the direction of the net force to the direction of acceleration, so took some steps to help reinforce those connections. When students asked me for help with a motion map, I started by having their group show me what they did to produce the motion. Next, I moved their bowling ball slowly through what they showed me pausing at “snapshots” that should appear on the motion map, which lead to a lot of students saying “Ooooooh!” in the way you know something is clicking for them.
A particular spot where students often get stuck is getting the bowling ball to move with a constant velocity. They often convince themselves the bowling ball is slowing down, therefore they need to keep tapping it at regular intervals. When I spoke to groups, I started by pointing out the way they got the bowling ball moving with a constant velocity was very similar to the way they got the bowling ball to accelerate. Students point out that for a constant velocity, they used very gentle and/or very infrequent taps, which leads to the question of how much the bowling ball is really slowing down if they don’t have to do much. To answer that, I pulled up Motion Shot on my phone. In the past, I’ve projected an image made in the app when we got to constant velocity in the class discussion, but this time I made the image live in front of students, which seemed much more impactful and helped students draw connections to the motion maps. Next year, I think I’ll pull out the app when students are having trouble with other motion maps, too.
My students haven’t had a lot of confidence in their lab results this year, even when they are doing great work, which I think is one of the barriers to sensemaking. To help with that, we took some time to whiteboard the motion maps students drew, including adding arrows to the motion maps to indicate when and which way they tapped the bowling ball. I usually skip this step, but it turned out to be a good opportunity for students to feel more confident about the motion maps they drew and to start noticing patterns they can use to formulate a version of Newton’s first law.
The other step I took to get students more confident in their results was to have them do a short activity I designed on Pivot Interactives using a PhET simulation. In the activity, I asked students to produce some similar motion to what they’d done with the bowling ball, then explicitly compare what they did in the sim to what they did with the bowling ball. I haven’t done many sims with this year’s students, but find students who struggle in the lab tend to put more trust into simulations than results they get with physical materials. Seeing that the PhET simulation produced very similar results to what they’d already done with the bowling balls seemed to give my students more faith in their results, which gave them the confidence to state that objects will go at a constant velocity unless a force acts on them before I gave them Newton’s 1st Law myself.