## Day 68 – Phrustrating Physics

Physics 11 – Today we had two main tasks. First, the students wrote a quiz with 4 different learning objectives: drawing force diagrams, determining if forces are balanced or unbalanced, knowing what vectors are, and Hooke’s Law. In general the quiz wasn’t done very well and since there were four learning objectives, class overall averages dropped by almost 5%. I think many students simply did not study.

We also finished the Fnet lab and analysis. I’m very fuzzy on whether it was worth it.  These videos are best used as secondary teaching tools, but I used it as the initial tool since we don’t have good (ie any) lab equipment for Fnet experiments. I really hope to get some probeware next spring so we can do labs like this hands-on. Doing this exact lab with probeware means that:

• lab software shows the x-t and v-t graphs instead of abstract numbers and calculations
• each group can ran multiply experiments with relatively quick data collection
time can be spent on analyzing and thinking, instead of calculations

## Day 66 – Fnet Direct Measurement Video

Physics 11 – Students analyzed a video which shows a fan cart accelerating on a low friction track. Through some data recording and calculations students were able to find the force of the fan and the acceleration of the cart.
I’m very unsure of the usefulness of this lab activity. The real goal of seeing and thinking about force and acceleration is likely being lost in calculations and figuring out what is going on with the video.  Stay tuned for next class…

## Day 64 – Last Day of Lab

Physics 11 – It was a long road, but today the students finally finished their unbalanced forces lab analysis.  This took a lot more time than I had expected, and I would say that the work ethic has been pretty good.  Lots of kids were getting a bit mixed up with their data and calculations, so there were several times where I would grab their data tables and quickly calculate acceleration and graph in Excel. I had thought about showing kids how to use Excel, Desmos or Plotly, but opted to stick with pencil and paper.  Learning to use this kind of software would take another day of time. Heck, I even find Plotly and Desmos confusing at times.

I’m really wondering if it is worth all of this time to do a lab on unbalanced forces….

## Day 62 – DMV for Fnet Lab

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.

## Day 61 – Direct Measurement Videos

Physics 11 – In preparation for the paradigm lab for unbalanced forces, today’s physics classes used Direct Measurement Videos (DMV) to analyze constant acceleration motion of a toy car.

The DMV we used were from Peter Bohacek at Carleton.  They are, simply put, brilliant.  Peter started making these videos a few years ago and in their most basic form, DMV are quite simple.  You shoot some video of an object moving and make sure there is some type of ruler in the scene.  Better videos will be shot at higher frame rates with better lighting, better apparatus and setups with very little lens distortion or perspective.  Once you have a video, you can analyze time (counting frames) and position.

Peter’s newest videos are put into an html5 video player with many more features.  For today’s class the DMV player we used allowed the user to pick different toy cars to analyze.

It took the whole class for students to get used to the software and gather data for analysis.  They were asked to find the acceleration of the toy car, but lots of students started collecting massive amounts of data and plotted position vs time graphs.  This was after we had a class discussion on how acceleration can be calculated directly from d = vot + 1/2at^2, or a = dv/dt, once you find the beginning and final velocity.  I’m not sure I’ll ever quite understand how students get off track so often (well, I think I know why, I just don’t know if I’ll ever get good enough to mostly eliminate it).