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07 January 2010

Assignment: Write your OWN dang test.

Writing a physics (open response) test question is not in any way an easy task.  It's hard enough to think of a new situation that provides interesting physics, and figure out solvable questions regarding that situation.  It's even harder to write the question so that it's solvable in 10-15 minutes and clear, with no possibility of misinterpretation.

Students get so caught up in the solving of these problems that they fail to appreciate the elegance of their design.  All they see are tough problems to which they have to get the right answers.  It doesn't necessarily occur that, while the details and values are different every time, each problem fits a narrow range of overall themes.  Johnny might be fully capable of dealing with an inelastic collision problem; he might be downright good at projectile problems.  Yet, put him under the pressure of a test, give him an inelastic collision that occurs on the end of a cliff, and ask him how far from the cliff the objects land?  Johnny is likely to be overwhelmed, and freeze like a Microsoft OS with more than one Window open.

One of the many ways I try to debug Johnny is the activity I'm finishing up this week in my general physics course:  the Student-Written Test.  Each student spends lots of time in and out of class writing 4-5 carefully prepared problems for possible use on a test.  I collect these problems, grade them for correctness of solution and quality of presentation, and give them all back.  A day or two later, I give the class a test consisting of three authenticly student-written problems.  (Sure, I adjust wording for clarity, but I use these problems as much verbatim as is reasonable.)

By the end of this one-two week process, my class has developed a serious appreciation for what it takes to write a physics problem... but more importantly, by writing problems of their own, they've become more comfortable dealing with extended multi-topic problems.

Below is the assignment as I handed it out last year, complete with a detailed schedule.  Feel free to use this... I find that I don't usually have time for this sort of thing in AP physics, but the general class can afford to slow the pace.  Besides, what better way to review the topics from the first four months of school?

Problem-writing assignment – instructions and schedule

Your assignment is to write 5 test-quality physics problems, using the concepts we’ve studied so far this year:

Motion graphs
Kinematics in 1-d
Kinematics in 2-d (includes projectile motion)
Newton’s second law
Newton’s second law in 2-d (includes inclined planes)
Impulse-momentum theorem
Law of conservation of momentum
Definition of work
Work-energy theorem

You don’t have to use all the concepts, but those are all available to you.

A test-quality physics problem is one that involves more than a simple plug-in to an equation. Often, more than one of the above concepts will be required to solve the problem. Looking over past test problems should give you a good idea of the level of complexity you are going for.Writing a test-quality problem is not a simple exercise. As you may have noticed, test problems involve more than simply plugging into an equation. Yet, a test problem must be solvable in 10-15 minutes, so you can’t ask anything horrendously complicated. Finding the balance between solvability and complexity, and meanwhile making every problem interesting, is your challenge.

The structure of a problem will usually follow a standard form. First, you’ll draw and describe a physical situation; then, you’ll ask several different questions about that situation in parts (a), (b), etc. To determine whether your problem has the proper scope and level of difficulty, consider how many of the above physics concepts must be used in the solution. Each problem should involve two or three concepts – no more, no less.

Writing a problem will involve several steps:

1. Think of a situation that provides fertile ground for asking physics questions about it. The situation should be able to be depicted in some sort of picture or diagram, which you’ll need to make (you may draw this freehand or with the aid of a computer drawing program). We’ll call this picture and short, written description of the situation your problem sketch.

2. Next, you’ll want to identify what your problem is asking the solver to find. You’ll also want to come up with reasonable values for whatever given information you are providing the solver, and you’ll want to determine how the question(s) will be asked. This is your draft.

3. Finally, you’ll take your draft and put it into finished form. To do this, you’ll have to check over the draft to make sure you have described the situation adequately, provided all the necessary information, and asked the question(s) clearly and unambiguously. Also, to be absolutely sure you have included everything you need to include, you’ll need to solve the problem yourself. This carefully proofread version, including your written-out solution, is your final problem.

The items due here are in addition to the homework problems assigned for this Monday, Wednesday, and Thursday.

Monday, 1/12: 2 sketches due

Wednesday, 1/14: 1 draft, 1 more sketch (3 total turned in)

Thursday, 1/15: 2 more drafts (3 total turned in), 2 more sketches (5 total)

Friday: 2 more drafts (5 total)

Saturday: 5 final problems

Wednesday, January 21: 45-minute test made from student-written problems

After you hand your final problems in on Thursday, I will look at all of your problems. I will grade each problem on a 5-point scale and return them to you on Monday.

On Wednesday, there will be a three-question test composed from questions you have written. The questions we choose could come from either class. We may do some rewording of the questions for the sake of clarity, but the physics content will be exactly what you wrote, with the solutions you devised.

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