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## 08 January 2014

### Quiz: How to read a labquest's motion graphs

It's all well and good to teach students to interpret motion graphs.  We should, of course, go beyond simply asking whether a, v, and x are positive or negative -- we should demand verbal descriptions of motion.  We should ask what kind of object is represented by the graph.  We should expect students to use normal language, such as "traveling east" and "speeding up" rather than, for example, "going positive" and "acceleration congruent with motion."

I find that my students, even my freshmen,* get pretty good at interpreting motion graphs on homework.  However, in the laboratory, their skills sometimes vanish.  They use a motion detector on a cart on a track, then tell me with a straight face that it started at 50 m/s, slowed down, and stopped after 0.05 s.  Or, they assume that the vertical axis reading on a position-time graph tells how far an object moved, not its distance from the detector.  These are mistakes I've ground out of the class on sterile homework problems, but not when confronted with a labquest reading.

*ESPECIALLY my freshmen

I'm not going to wax poetic about why misconceptions persist in new contexts despite a physics teacher's best efforts.  Rather, I'm going to keep my efforts coming.

Today we have an (announced) labquest quiz.  I've taken four photographs of actual labquest readings.  For three of them, I ask students whether it's a reasonable graph, and why.  For the fourth, I ask for a calculation of distance traveled, and for the duration of the cart's travel.  These are all questions I've asked repeatedly in class when a student shows me data.  However, now I'm checking to see who really understands, and who just nods his head in the hope that I'll shut up.  :-)