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[Phys-L] Re: student difficulties with velocity as a vector?

On Mon, 24 Oct 2005, I wrote that my students were having difficulty
identifying the "vertical initial velocity" of a ball rolling off a
horizontal table.

On Monday, October 24, 2005 5:36 PM, Herb Gottlieb wrote:

it is apparent that some of the students may have had trouble
because they assumed that the ball encountered air reistance
on the way down through the air surrounding the table.

This is intriguing but I don't see how this would cause a problem with
identifying the "initial" velocity. Can you be more specific?

On Monday, October 24, 2005 4:33 PM, John Clement wrote:

Perhaps a look at the latest McDermott paper in AJP would be
enlightening. She points out that even graduate students have
difficulty with vectors and kinematics.

I'm not convinced the problem lies with vectors and kinematics as
opposed to language or reading (i.e., meaning of "initial") but I'll
look into it.

Another point is that instead of going over each question
when asked using a classroom response system, it is suggested
that students discuss it, revote, and then a student should
give the final summary.

I agree with that suggestion and I routinely do so. I didn't do so in
this case because I was trying to identify the root cause of their
difficulty in a related matter. I wasn't trying to address it at that
moment.

This question is actually analogous to one on the FCI, and
apparently evoked a common misconception.

Which FCI question? The cannon-ball one or the two metal balls rolling
off the table? I'm not sure if the difficulty is the same but I can
look into it.

There is also the
problem that you are asking for two variable reasoning. If
you gave the Lawson test of scientific reasoning you might be
able to see if the wrong answers correlate with wrong answers
on the two variable reasoning questions.

I used to give some of the Lawson questions but didn't try the
two-variable reasoning ones. I'll look into it.

On Friday, October 28, 2005 11:56 PM, Jack Uretsky wrote:

OK, Robert, I've been there. Your mistake is that you assume
that what you explain in class is relevant to the student
answers. What you are really measuring, IMO, is not the
student understanding of Physics, bu the fraction of students
who pay attention during your lectures.

Dick Hake partially addressed this question in his TPR
article on the SDI labs and the inneffectiveness of even his
most brillian lectures.

My question was not on the weaknesses and strengths of my teaching
technique (which I didn't mention except that I use student remotes) but
rather on the difficulties the students are experiencing based on their
results on the questions I posed. Regardless, Jack is perceptive enough
to have found me out. Whereas I usually barely lecture at all, I have
tried this semester to implement more lecture in order to see what it is
that I do that makes it as effective as it is. I've been able to
achieve high gains on the FCI and an internal survey we've been using in
our department but it isn't clear what I do that makes me so much more
successful than my colleagues. I am also not sure if my students before
would've done any better on this particular series of questions - I
never bothered to ask.

My students, by the way, score at around 25% on the FCI before
instruction and I suspect part of the problem is their reading ability.
For example, I believe the problem with the question I posed in my
previous message was with interpreting the word "initial" rather than
with calculating the "vertical" component of a horizontal velocity.
I've also found that my students have difficulty distinguishing between
(Delta v), v_avg, v_i, etc. For example, I once asked students to
consider an object that starts from rest and accelerates at a constant
rate. If the change in velocity is 122.5 m/s toward the north, what is
the average velocity?
A. 245 m/s [0%]
B. 122.5 m/s [61%]
C. 61.25 m/s [39%]
D. zero [0%]

Further thoughts?

____________________________________________________
Robert Cohen, Chair, Department of Physics
East Stroudsburg University; E. Stroudsburg, PA 18301
570-422-3428; www.esu.edu/~bbq