I graded the forces exam for my college-at-my-high-school physics course over the last couple of days, and once again I was very pleased with the results. Here is a dynamic version of the graph above.
I attribute the gains I saw in this and the first exam to implementation of modeling instruction last year and a modified version of Standards Based Grading this year. To be truly transparent, the exams are a bit different year to year so it is difficult to make true comparisons, but the data so far is consistent for both exams, as well as with my qualitative observations that this year’s group has gained significantly in problem solving ability (again, see the SBG post). The FCI will be the true test of students’ conceptual gains, I’m excited to give it later this year.
Today I finalized my Projectile Motion Packet, once again with heavy borrowing from Kelly. I realized after reading her post about model building that I was able to cut a bunch of fluff from the unit, which is awesome because I’m more than a week behind compared to last year and this allows me to catch up while offering my students what I think is a better, more concise model building experience.
Above is student work where they are deriving a formula relating the distance d the middle mass drops as a function of the middle mass M. It is a good exercise for them to derive the formula, and a fun lab because the trend is usually very good (and it’s a nasty radical function that LoggerPro handles beautifully!) but there is significant systematic error.
The lab is P3 from Lab III here, though I modified the handout to do the force analysis first and then substitute the lengths for sin(theta) later.
Today some students and I attended the Physics Force Physics Circus demonstration show. In the picture above they are preparing for the life-size monkey and hunter demonstration, my favorite, video below.
I stole another page from Kelly and set this lab practical up as a quiz. The students were told that I would give them both angles and the starting location of a cart on the steeper ramp; their job was to find a formula giving the location of the cart on the shallower ramp such that the carts hit the end stop at the same time.
This is great as a quiz for three main reasons
- It combines multiple models into an interesting problem
- If students get it wrong, they find out physically and can retry the problem if they have time
- It’s awesome to see physically when they get it right.
The picture below has students in the forefront plugging the given values into their formula to prepare for testing (hence the calculators), and students in the background looking at the solutions (yellow sheets), either they already tested correctly or they got stuck. I had a couple of students nail this who have been struggling. It is extremely satisfying seeing the carts hit in the right place.
***Note: This situation is fairly easy to get ‘right’ doing the wrong physics (or by just guessing with a ratio of angles). I always looked at their papers first, and if their answer was close to correct with the wrong work, I cheated and gave one cart a bit of a push at the release so they didn’t hit at the same time. I confessed this to the students later.
A more dynamic view of this collage is available here.
Today we were working on a problem (#4 in Practice 3 in here) and I wanted to investigate the situation a bit more closely. The problem is a modified atwood, and I had one set up with a wireless force detector on a cart, so the situation was different than the problem in that it was essentially frictionless. I showed students what the F vs. t graph looked like when I just held the cart (a horizontal graph, as F is constant). Then I asked them what would happen to that graph if I released the cart. The above is what they drew, below is what actually happens.
After taking the above data students discussed why this occurs using qualitative free body diagrams of the hanging mass before and after the release.