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.