This week was all about starting to build a model of forces. We started by tapping bowling balls with mallets, using a version of the activity based on Frank Noschese’s. Students were quicker than usual to recognize that they had to juts leave the bowling ball alone once it was moving to keep it moving at a constant speed, but I still pulled up an old image I made with motion shot to get some additional evidence. After that, we moved into a version of interaction stations from Kelly O’Shea where students identified forces based on stretch, compression, and shear. Finally, we wrapped up the week with some mistakes whiteboarding with force diagrams. When I introduced system schema and free-body diagrams, I didn’t emphasize enough that the free-body diagram only needs to show forces that cross the system boundary, but that lead to some great conversations during the whiteboarding as students figured out what they needed to include. One student commented that almost all of their mistakes related to including more than they needed to, which lead to some nice discussion about the fact that the hardest part of physics is often figuring out what is relevant.