Today was the second day of the Balanced Forces Particle Model (BFPM), which I intro using Kelly’s rather brilliant method here. This is a picture of the whiteboard after one of the classes, we didn’t quite finish looking at the pattern but were able to leave my last classes’ on the board for tomorrow, where we will finish drawing out the connection between Forces and our former models, Constant Acceleration Particle Model (CAPM) and Constant Velocity Particle Model (CVPM).
As I was grading this years Exam 1 in my concurrent enrollment college level physics class I had a feeling that students were really rocking it compared to last year, so naturally I spent 1-2 hours on a Saturday night playing with the data. This box plot is, I think, the best representation, showing that all four quartiles increased. This is verified in that the mean had a statistically significant increase (p<0.05) and the standard deviation decreased from around 13 to 9.
I am in the process of writing a blog post about why I believe this increase of scores occurred, so you’ll have to wait a bit for that. The teaser is that it’s a kind of Standards Based Grading (SBG) implementation for a class in which I can’t really do SBG.
UPDATE: Here’s the blog post, When You Can’t Do SBG
Today Ben walked into my office with an assumption that students were making. They were working on problem 1c from Practice 1 in this packet, where a concrete block is being pushed with a hand, and there assumption was that the block sped up instantaneously and then moved at a constant velocity while the hand pushed. So Ben and I went back to the classroom and recorded a high speed video of a box being pushed, and the results above are pretty convincing that the box sped up. We want to make a better video with a large, heavy box, but this worked for the time being.
We are working on testing the effect of mass on acceleration for a cart down a ramp, and students are going to write a lab report for this lab. One group came up with the great idea to keep all trials on the same screen, giving great qualitative evidence that the acceleration is not affected by the mass.
I just finished up (I hope) this year’s BFPM packet, borrowed heavily once again from Kelly. I am particularly looking forward to whiteboarding the problem above, it’s going to be pretty tough for students. I’ve recently had a lot of luck writing problems based on images I find with simple Google searches like “Two boxes ramp physics.”
Today I built a reassessment day into our schedule. I have 74 kids in this class (in 3 sections), and I printed out 55 reassessments on 4 different learning targets! The gains they showed were impressive; approximately 80% increased their score and the other 20% showed some gains in understanding even though it didn’t change their score (I grade 2,1,0). More on my grading system coming soon on learningandphysics.wordpress.com!
Today I was gone, and students were investigating adding mass to carts going down a constant incline. They apparently took it to the extreme.
I got permission from my principal 2 years ago to join a student created FB group with students in my class and it is awesome for community building and quick announcements. If you are not familiar with groups, you don’t have to be ‘friends,’ so we can’t see each other’s normal FB activity, only what is posted directly on the group page.
Today we worked on a capm lab practical. We first found the acceleration of a cart down a ramp. Then we took down the motion detector and I showed them two photogates. The photogates measure the change in time between them (among other possibilities, but that’s all I showed them for now). The students must choose a starting location for the cart on the ramp that is at least 10 cm above the first photogate, then find where the two photogates should go such that the change in time was some particular value, different for each group. As you can see above, this went swimmingly in third hour. The other two, however, were failures on my part.
First hour I tried to go over a problem we worked on yesterday first, and then students didn’t have even close to enough time to do the problem and test it, especially because I only had one photogate setup that I had planned to move around to all the different ramps. In 2nd hour I skipped the problem at the beginning, but I still used different setups for each group and it proved impossible to move it around. For third hour we just found the acceleration of one setup as a class, then I gave them all different times and they only had to adjust the photogate location on the one setup to test. This worked MUCH better.
One thing that surprised me was how well this worked. The groups that did the calculation correctly were closer than a hundredth of a second off. It is very difficult to get the photogates in the right place, as they are 10 cm above the track. I figured there would be a bit more uncertainty; but the first group that did it right is the one that was right on, to the thousandth of a second! We all agreed there was a bit of luck in there.
Today we were solving The Raptor Problem and one group came up with the possibility for an interesting way to solve it. The shaded region represents the displacement from the raptor to the person, getting bigger before the velocities are equal (but less big as time goes on) and getting smaller again after the velocities are equal. I thought it was a neat way to approach the problem.
We’re getting toward the end of CAPM and I’m very impressed with the gains I’ve seen in problem solving ability. These kids are getting pretty good and solving problems using both algebraic and graphical methods. This particular problem was fun because we were able to take a closer look at multiple aspects of the boxed, derived equation. The graph below represents some aspects of it, though it’s a bit hard to tell. The red box is the term, representing the displacement if the object continued at a constant velocity of . The term is the purple shaded region; negative because is negative. Thus the displacement, as depicted by the area of the black triangle, is the red rectangle minus the purple triangle. Cool.
We then went on to show that their equation actually simplifies to , which is then represented by the green rectangle. I love algebraic and graphical connections!