Describing a procedure concisely

From Homestarrunner.com.  Don't get the reference?  Check out
"English Paper" at the homestarrunner wiki.

Much of the physics teaching world, and I, have leapt away from multi-page, badly written "formal lab reports."  Instead, it's typical now for students to be asked several directed questions about an experiment.  Formal lab reports are only useful if the instructor takes the time and energy to truly teach the scientific writing process -- that means grading drafts, participating in writing conferences, paying as much attention to style and language as to results.  I decided long ago that the benefits of the formal lab were in no way worth the costs.

That said, I still do teach a few writing skills.  Particularly, my class learns how to describe an experimental procedure while defining relevant variables.  AP exams, as well as my Honors Physics exam and even the Regents exam, occasionally ask for a description of an experiment.  Your class needs some minimal tutelage so that these questions become easy rather than time- and stress- consuming.

Describe the procedure you used to measure T, q, and any other relevant parameters.

This is a question I ask after our first experiment, phrased identically to the style of an AP question.  I explain to the class that they should use no more than three sentences, telling me in prose what they measured and how they measured it.  I expect an answer such as:

We kept a cart in place on an inclined track using a string held parallel to the track.  The tension in the string, T, was measured with a spring scale tied to the string.  The angle of the incline from the horizontal, q, was measured with the "clinometer" iphone app.

Note how everything, including definitions of variables, is included as part of the prose.  Some folks want to just give a list of variables* ; they lose considerable points in my attempt to get them to write sentences.  

* "T:  measured with a scale"

But consider what I often see at the AP reading, or after my class's first experiment:

We came into lab today in order to find the tension in a string when we hold a cart at many different angles.  First we found are partners; I worked with Joe.  Then we gathered our materials:  A 250 g cart, some string, scissors, an aluminum track, and a spring scale.  Goggles should be worn, as always in the laboratory.  We tied the string to the cart, being careful that the string could be held parallel to the track.  Joe tied a sailor's knot so that we could attach the spring scale to the cart.  I downloaded an app from the itunes library that shows an angle.  Now, with all materials in place, we could begin the experiment.  Joe carefully read the scale to the nearest 0.2 N, and he wrote down both readings in his notebook.  Finally, I graphed the data on a graph with a pencil, which I forgot to include in my materials list above.

[Is it considered satire if it's true?]

My purpose here is not* to make fun of a student who would write the above passage.  The question is, how do we get this student to write a proper, brief, clear, 3-sentence procedure?

*primarily

I've had some success reminding the class of their audience.  They are not writing a "how to" manual, they're not writing for their English teacher who is ignorant of laboratory methods; the audience for a laboratory procedure is OTHER SCIENTISTS.  I make the audience even more concrete by identifying a recent alumnus: "Peter Chen, whom youall know took my class last year, should be able to figure out what you measured, and how you measured it."  They see with minimal prodding that Peter doesn't need to be told to gather materials.  Peter doesn't need a silly safety lecture.  Peter doesn't need to be told to record data carefully -- we take all these basic "skills" for granted, because we are scientists.  

The other useful reminder is about time.  A procedural lab question like this might be worth three points on an AP exam.  At the going rate of one point per minute, the test expects a few minutes of work -- no more. If you spend a lifetime writing multiple paragraphs, even if such paragraphs are pulitzer-prize worthy, you will earn... three points.  And you will NOT earn the other seven points available in this problem, because the bell has rung, the sun has set, and the exam is over.

It's important to model the correct writing style for the class at some point.  This is a different kind of writing than their English teacher has required -- after all, I used no drama, no interesting transitions, nothing about my feelings.  They have to see for themselves that it is okay to be short and "boring."  

And finally, perfect practice makes perfect.  Some folks will ignore all your advice until you take off points; then their next writeup will be perfect.  Others will need a figurative bashing over the head.  But with patient, persistent work, you can get your students comfortable with describing experimental procedures.

GCJ

Equal length spring set

I hate doing unpaid shilling for deep-pocketed companies.  However, when PASCO provides exactly the right tool for teaching a physics concept, as they so often do, I can do nothing but spread the good word.

Take a look at the three springs you see in the picture to the right.  All are clearly equal in length and diameter.  They seem identical in every respect except color.

But when I hang a 500 g mass from each spring, the springs stretch different amounts.  The spring constants can be ranked, calculated, used for prediction of extension under a new load, etc.  What a great lab tool.

PASCO sells a five-spring set via the link here.  The red, blue, and yellow springs have a book value spring constant of 25 N/m, 30 N/m, and 35 N/m, respectively.  In my picture, the yellow spring is slightly less stretched than the blue one, but only slightly.  Well, that's okay, because (a) the yellow spring is supposed to have a larger spring constant than the blue spring, and (b) PASCO only lists the accuracy of each spring constant as +/- 5%.  It could well be that the blue spring is at the top edge of the 5% tolerance, or about 1.5 N/m too high; the yellow spring might be at the bottom edge of its tolerance, putting the stretch close to, but not quite, identical for each.

Now, for years I've used cheap-o springs that I bought in bulk from random sites online.  But these springs get stretched past their elastic limit, intertwined with other springs, and generally destroyed very quickly.  PASCO's set of five springs comes in a storage box, and these springs are tough to tangle.  Plus the color codes allow you to determine very quickly how carefully a lab group has done an experiment.  I'd suggest getting at least a demonstration set of these, if not a class set, unless your budget is lilliputian.

I always argue that physics equipment should be bought over many years, a few pieces at a time.  That's not the reality of most schools' budgeting processes, which generally give more money than you know what to do with all at once, but then nearly nothing for years on end.  That's simply not practical.  You want to be able to buy new toys when you find out about them; don't buy too much at once, spread your purchases out over the years.  

Well, my colleague Curtis bought a set of these, and now I'm jealous.  Good thing we ordered another set for me for next year...  Thanks, Curtis, and thanks, PASCO.

GCJ