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.