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04 July 2009

Revising my general physics laboratory program

Over the years, my AP physics labs have meshed into a true PROGRAM. That means not only are the individual experiments worthwhile, but that the year’s set of laboratory exercises serves to develop and reinforce a set of worthwhile skills. When the students start to roll their eyes at me as if to say, “yeah, yeah, we know what to do now, we’ve done it a dozen times,” I know that the lab program has been successful.

My AP lab program is designed to teach the lab skills necessary for the AP exam. Most prominent among these is the process of linearizing a graph, and using the best-fit line to determine an unknown quantity. That’s an important and useful skill…but one that is above the heads of my GENERAL physics students, at least at year’s beginning. For general physics, I have an entirely different set of experiments, each one solid, but without any guiding theme. In other words, my general physics labs in no way constitute a PROGRAM.

My summer mission is to begin to change this shortcoming: I want to revise my laboratory exercises so that they all mesh together. Specifically, I am going to try to use the “recurrent” lab model, as presented by Mikhail Agrest in The Physics Teacher, and as discussed earlier on this blog. My goal is for most of my experiments to ask students to use the result of their measurement to make a testable, high-stakes prediction.

[As a brief aside, note that no one is standing over me demanding that my lab exercises meet any particular “inquiry objectives” put together by “learning specialists.” No, I just have some time to invest for next year’s classes, so I’m working on general physics lab. I often see relatively new physics teachers become intimidated by the sheer volume of background work necessary to put together a strong physics course. The fact is, it takes many years before every aspect of your course will be successful. Partly this is because much trial and error is involved – I’ve wasted a couple of years here and there discovering why various physics teaching methods do NOT work for me. More to the point, no one has the time or experience to do everything perfectly right away. I’ve been teaching physics for fourteen years, and I’m only now coalescing my general physics lab program into something above the level of “adequate.” That’s fine – the labs have been adequate, and I’ve spent enormous amounts of time making other aspects of my course really good. Work on one thing at a time, and don't let anyone tell you you stink just because, say, your labs aren't perfect.]

The first topic of the year in general physics is position-time graphs. After nearly a week of lectures, demonstrations, and problems, the first lab exercise is to make a position-time graph for a “constant speed vehicle” using a stopwatch and metersticks. One goal of the experiment is to introduce my expectations for graphs in physics class, including proper labeling, as well as how to take a slope properly. Another goal is to give students kinesthetic experience with position-time graphs. They see that the slope of the position-time graph is the velocity of the vehicle, just as they’ve learned on homework.

What am I going to do differently this year? After each group has calculated the slope of their position-time graph, I will ask them to predict the position of the vehicle after it has been moving for, say, 10 s. Each group will give a location with uncertainty – i.e. 300 +/- 10 cm. Finally, *I* will measure the position of the cart after 10 s. Points will be earned for matching my measurement; more points, including some extra credit, can be earned for groups who match my measurement with the smallest uncertainty.

The second experiment uses “tape timers” to make a position-time graph for a cart on an incline. By taking the slope at several points, a velocity-time graph can be made, and used to find the acceleration of the cart. Except that this year, I will use a sonic motion detector to determine the acceleration of each group’s cart. Matching the acceleration that I measure will be a major part of the lab score.

You see? While every experiment won’t match this format, I’ll adjust as many as I can. You got good ideas? I’d love to hear them. Post a comment.


1 comment:

  1. Thanks for sharing your reflections on teaching physics. I'm a biology person thrust into teaching physics this year, and it's been an interesting challenge. The amount of background work -- the thinking behind each and every physics concept, and the conceptualizing of how to get students to envision and understand (and in my dream world, enjoy) each physics component -- has been overwhelming. Thanks for reassuring us that it does take a while to get it right. - John