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22 July 2009

Mailbag: Writing in physics class

The Nachograndpa, a.k.a. mathematics professor Dr. Barton Jacobs, writes:

"I now have a question that came up with your Mother regarding her English 101 class, where they're supposed to learn how to write for a variety of categories of writing. I said that beyond Freshman Calculus, all math courses require putting together an argument that entails as much in the way of English words as it does symbols. I had vaguely remembered that as early as Freshman Physics this is also true. Is that right?"

Yes, but not in the same ritualized manner as, say, a geometric proof. We do enormous amounts of writing in my class, and I don't mean just lab reports. A typical question on an assignment might be,

"A ball is dropped from a table. The height of the table is now doubled. What happens to the time it takes for the ball to hit the ground?

___ the time increases, but does not double
___ the time doubles
___ the time more than doubles

Now justify your answer."

The "Justify your answer" questions generally require verbal discussions with reference to formulae. I have the dangdest time getting my students not to BS, but to use no more than two sentences with reference to the relevant equation.

The correct answer is that the time increases, but does not double. The justification: "The kinematics equation can be solved for time to get t=root (2x/g). Since we doubled the quantity under the square root, the time to fall increases by a factor of root 2 rather than 2." That's a fully sufficient explanation! But most folks want to go on for paragraphs... why?

Usually because they're not quite sure, and their experience in other classes is that if you write enough with sophisticated-sounding vocabulary and phrasology, the instructor will essentially throw up her hands in despair and award credit. Problem is, on the AP exam at least, incorrect statements interspersed with correct statements will always lose credit; correct but irrelevant statements cannot earn credit. The logic has to flow properly; getting it to do so is as much a writing skill as a physics skill.

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