Once again, a little behind on the update of the teaching journal. This week’s excuses: tests in E&M and my introductory particle physics class, in addition to grading the first round of lab reports plus the re-writes. We’re definitely in the thick of the semester now, but at least I have spring break to look forward to in a week. Of course, I have to make it through my quantum midterm before then, but that’s a different story.
Now, on to the Teaching Journal:
Coming up with a good problem for this type of discussion is difficult. You want to make it doable, but not too simple. You want to encourage critical thinking, but you have to give the students enough to grasp onto, or they will freeze up, and look to the TA to tell them what to do. It’s a tough balance. That’s why I’m glad that writing these problems is not my responsibility.
I bring this up, because the problem for this week straddled a lot of these lines. The thing that I liked best about it is also the thing that the students hated the most: it was an open-ended problem, with no set answer. There were many assumptions that the students had to make, and there were several quantities that they could examine to help decide if the situation presented (involving a superhero, naturally) was realistic or not.
I like this type of problem, because it shows how a physicist has to think. They are not canned problems, with an answer that you can check in the back of the book. You can’t even look at the title of the chapter to see what concepts might be involved. It’s just you, your toolbox of concepts and equations, and your creative approach.
The students hate this. They ask me what assumptions they need to make, what concepts or quantities I want them to look at, or, worst of all, they ask what equations to use. I tell them as little as I can, but if I’m too mysterious, I get blank looks, and the students just sit there, telling me they don’t get it. As a result, I end up directing them down a path more than I would like. The problem with this is that it perpetuates the idea that there’s a certain way to solve the problem that they need to figure out, and the mysterious cues that lead to my approach can remain obscure.
I wonder if these types of problems would go over better with students who are more intersted in physics for its own sake.
Lab this week was also interesting, interesting enough that I assigned it for the second lab report. The setup is a cart on a ramp, with a hanging weight pulling on one side, and a spring pulling on the other. The goal is to measure the spring’s force constant.
Not a particularly exciting setup, right? But the key point that I want them to learn here is how to measure a quantity by making a graph and finding a linear fit to the data, an emportant experimental skill. In one case, they will graph the spring’s extension vs. the hanging mass, a linear graph whose slope is related to the spring constant.
The other situation is even more interesting. If we graph the spring’s extension vs. the angle of the ramp, we get a curve that is difficult to fit. But if we graph extension vs. the sine of the angle, we get a nice linear relationship, and we can again relate the spring constant to the slope.
This sort of thing happens all the time in physics experiments, because linear relationships are much easier to fit accurately than any other type of curve.
Whew, that’s a lot for Week Five
The discussion this week was a group problem for the second quiz. It involved concepts of force, friction, and acceleration, and really was fairly straightforward. Except for one thing: the problem asked which of two motors could perform a certain task, and the correct answer was that neither could. Some groups trusted their approach and gave this as their answer, but some were freaked out by this and changed their answer. Sometimes you just have to trust the physics concepts you’ve used all along to give you the right answer.
Lab this week was fairly unremarkable. The first problem had the students look at circular motion, and the sinusoidal motion that results. The other was a pretty basic conservation of energy problem that for some reason didn’t give very good results. But since this post has already gone on this long, and I didn’t find this lab all that compelling, I’ll just leave it at that.