Physics 11 – Having become familiar with DMV for direct measurement, today I had the students analyze unbalanced forces as a substitute for the modified Atwood machine lab. The modified Atwood machine poses a few obstacles for understanding. First, it’s kind of hard to set up unless you have several sets of cart tracks and pulleys (we don’t). You also have to instruct students to keep the system mass the same (hand waving). You also need some decent technology to for measuring time and position (ie motion sensors or motion encoders), or your results go a bit sideways. I think ticker tape timers work quite ok for this type of lab, but only if the students have played and experimented with the timers before.
This year I wanted another try at doing the unbalanced forces lab so I went the direct measurement video path. The lab instructions were posted as seen above, and I introduced the DMV to them. To my surprise, many students continued to have problems finding the acceleration of the cart, they started collecting all sorts of data about position and time. We worked through it and by the end of the class all the groups had data, some groups had calculated acceleration and Fnet for each case, and some students even started graphing.
Physics 11 – We’ve covered a bunch of little topics to date in forces: Fg, Fs, FBD. I felt that today was time for some more practice, and I could tell from student questions while they were working away that this was a good time to go over some problems. We also did a quick activity with masses and spring gauges to emphasize the difference between mass and force of gravity.
Physics 11 – Today the students combined some skills and understandings they’ve been working on: drawing a force diagram, determining if forces are balanced, and then finding unknown forces by knowing that Fnet = 0.
Physics 11 – Students did more work on FBD and vectors, with calculating some horizontal and vertical forces using trigonometry.
This question also came up from the modelling package. I wouldn’t expect many kids to get this question correct, I think it is very unintuitive. However, it’s a great question to go over in front of the class.
Physics 11 – Students drew force diagrams and we extended this activity to analyzing forces acting at an angle. Students began to look at how an angle can be analyzed in separate vertical and horizontal components. I think this is a good place to start with vectors and components because the force vector is static.
Physics 11 – Today was the students’ last day at analyzing gravity. They worked towards the understanding that big objects and small objects exert the same gravitational force on each other. This will also become a valuable lesson when it is extended to the more general case of all forces and interaction pairs.
Physics 11 – Today the classes worked towards whether or not small objects exert a force of gravity on large objects. The above voting question is where the kids voice their understanding.
Two of my classes worked through this ok but one class really struggled. As a result, I typed out an argument/reasoning for them. I think it may have helped a few students.