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05 October 2015

How I'm starting my 9th grade AP course -- position-time graphs

Juniors and seniors like to sit still and take notes while I talk from the front of the room.  Sure, they want to be entertained and impressed by quantitative demonstrations, but nevertheless they don't initially appreciate active, open-ended classes.  It takes considerable work over the course of the year to convince upperclassmen to relax enough to deal with true "inquiry."

Freshmen, on the other hand... they are thrilled NOT to have to sit still.  They're willing to try things that they might get wrong.  And they're not going to remember much that you say to them from the front of the room, anyway, so you might as well give them an open-ended class.

In order to act on these observations, I now begin my AP classes for seniors differently than I begin my AP classes for freshmen.

For seniors, I begin with equilibrium.  I do demonstrations with friction, normal force, objects hanging from strings at angles... for each, I show how to predict amounts of force using free body diagrams, then we verify the predictions with scales.  These are strong classes, allowing my students to quickly figure out how to solve complicated physics problems, setting the stage well for the year's material.

But for 9th grade, I'm starting with position-time graphs.  I'm doing the very same exercise I do with my regular conceptual physics course, but over one or two days rather than four or five days.  

I briefly demonstrate the use of the motion detector with the Vernier labquest.  I hand out just the facts on this sheet about position-time graphs.  (I'll hand out the other facts later.)  I give each student a copy of this worksheet, as shown at the top of this post:  It has a position-time graph, along with three questions about the physical manifestation of the graph.  Each student gets a different graph, which I draw in by hand.  Some represent constant speed motion, some represent speeding up or slowing down.

Each student answers the questions on the worksheet one at a time, bringing the answer to me after finishing each one.  I either say "good, move on to the next question," or I explain the mistake in reasoning and ask the student to try again.  

Once all three questions have been answered correctly, I send the student to the back of the room to do the experiment.  Ideally, in a few minutes he comes back to show me a labquest with a correct position-time graph displayed.  See: prediction and experiment, all together in one exercise.  

After each student has done two or three of these, I give out a similar worksheet and facts about velocity-time facts.  And so I can teach motion graphs in just a couple of days.

I tried this activity with seniors.  They didn't like it... they were angry with me when I said "no, sorry, that's not right."  Even when I sent them to the back to do the experiment, even when they came back with results that didn't match the graph, they sulked, as if it were my fault that the carts and sensors didn't adjust to their lawyerly interpretation of the laws of physics.   No, open-ended, independent class work with seniors was a bad idea at the start of the year.  It caused the students to hate me as a proxy for hating the world.

But the wide-eyed freshmen on their first day of an intimidating AP physics course?  They were thrilled to be doing something hard but manageable.  They loved seeing whether their predictions were right or wrong.  They loved the confidence built by revising their ideas until the experiment matched their prediction.  

People wonder why I want to teach AP Physics to freshmen... and this is why, in a nutshell.  My freshmen are wide-eyed puppies, still thrilled by discovery.  Despite the difficulties of structuring an AP course for younger and less-experienced students, the enthusiastic cooperation from my ninth graders compared to the sullen grade-gaming of too many of my seniors makes any amount of extra work worthwhile.

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