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16 June 2015

Set up *ALL* AP Physics 1 problems in the laboratory.

"Laboratory" doesn't have to be a distinct part of a physics course -- it's just what we do, especially in AP Physics 1.

When I took high school and college science classes, "laboratory" was a special, separate portion of each class.  Most days the teacher would talk to us about facts and problem solving.  Once a week or so we would perform an experiment -- always going to a separate lab room in order to do so.  The laboratory portion of the course stood entirely separate, too, in terms of evaluation.  The idea of asking a test question in an experimental context was utterly foreign.  Sure, biology had "lab practical" tests in which we identified parts of a frog or worm*.  Those tests were still entirely in the experimental realm, just an alternative to a lab report.  A holistic integration of facts, problem solving, and experimentation was unheard of.

* Gross.  Now you know why I'm a physicist, not a biologist.

In the mid 1990s the AP Physics exams began including one question per exam based around an experiment.  Such questions required explanations of procedure as well as verbal and quantitative analysis of data.  I've often recommended to teachers that they could use these old test questions essentially as a laboratory course -- assign the AP questions on quizzes or tests, then use lab time to actually do the experiment.  

The AP Physics 1 exam also includes one free response question related explicitly to laboratory skills.  On the 2015 exam, that was question 2, about circuits.  It would be a simple matter to repurpose this question as a laboratory activity.  The first part asks for simple ammeter and voltmeter readings.  The second part asks students to determine whether a light bulb is ohmic -- my class did this exact experiment, graphing current vs. voltage, and found a clear curve.  

The hugely important point is, all five of the 2015 AP Physics 1 free response questions can be set up as laboratory activities.  

Question 1 asks for a qualitative prediction of how the acceleration of an Atwood's machine will change with added mass.  So set the situation up with two pulleys on a lab table, and use a motion detector to measure the acceleration with and without a cart included in the system.  

Question 3 puts a block on a horizontal spring, and asks for a graph of kinetic energy vs. time for the block as it leaves the spring and slides to a stop.  Use a compressible spring and a rough block on a track; a motion detector can record position and velocity data.  Vernier Labquests can be easily programmed to graph kinetic energy as a function of position, as on the test question.

Question 4 is the classic "does a fired bullet hit the ground at the same time as one that's dropped?"  Video analysis of this phenomenon is readily available.  A Mythbusters* episode was devoted to exactly this problem.  I use the ipad app "Coach's Eye" to record my PASCO projectile launcher shooting balls horizontally at different speeds.  The app shows conclusively that the balls hit the ground within a hundredth of a second of each other.

* Or perhaps it was a "Ghostbusters" episode.  Some students might have been confused on this account.

Question 5 is basically asking why each string on a cello or guitar plays a different note when plucked.  You could get some guitar strings and set them up over pulleys, exactly as in the problem. Then you could pose exactly the AP question as an open-ended, live-action laboratory activity.  No description necessary, though, just "Look here, why do these four strings play different notes?  Explain, and then do some sort of experimental test to see if your explanation is correct."

Last year in one of my summer institutes, we spent a morning setting up experiments to verify the answer to multiple choice questions on the released practice exam.  We found a way to do most of them.

The beauty of AP Physics 1 is that, with very few exceptions, all of the relevant topics lend themselves to classroom-scale experimental investigations.  They don't all have to be done as student-led, hands-on, multi-day laboratory activities, of course.  You can do quantitative and qualitative demonstrations from the front of the classroom.  You can have students make "quick and dirty" measurements sometimes rather than detailed graphs over a large parameter space.  You can collect and analyze data occasionally as a whole class rather than in individual lab groups.  

But you can and should do the experiments suggested by virtually every problem in AP Physics 1.  Fortunately, for me, the days of having one room for lecture and another for lab are long gone.  I don't teach a separate lab course, though we do perform a few extensive, multi-period projects along with quicker investigations.  My goal is to get student hands on equipment about three times per week, even if only for a few minutes on some of those days.

And what is my lab guide for all those 100 plus lab days?  Much of it is just the released AP Physics exams themselves.

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