[Phys-L] Re: Aristotelian thinking among modern students

[jbellina at SAINTMARYS.EDU (jbellina)]

I was away from email one day, and lots of folks had lots to say, and
all good things, and that is part of the problem.  This is one of
those cases in which there are a few ways to get it right and a
zillion ways to get it wrong.  This problem has no quick fix.
Saying the textbook should fix it, misses the point that textbooks
are generally delivery systems and engagement is the issue.  That is
why Dan rightly suggests Knight's workbook, even though the text
looks very good.
There are many alternative conceptions lurking in this issue, which
is why Rick says it takes so long, and even then it is not clear that
what they say in the end is what they really believe....change belief
systems is tough, getting them to say the right thing in class or on
a text is easier, and less permanent.
You need a systematic approach of engagement from the beginning,
seems to me we need a global campaign rather than a local stategy.
That is why perhaps engagements like workshop physics,  modelling or
a good workbook like Knights may be more effective than a better
textbook

joe

Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556

On Oct 20, 2005, at 11:28 AM, David T. Marx wrote:

> I am presently teaching a general ed course for mostly non-
> technical undergraduates (mostly
> freshmen).  Two-thirds of the students had high school physics.
> One half had calculus in high
> school.  The course is taught as primarily conceptual with examples
> and practice problems that use
> algebra and trig.  I gave a written exam last week covering
> Newton's laws, gravity, projectile
> motion, work and energy.  I give written tests rather than multiple
> choice tests so that I can see
> student's thought processes at work.  Sometimes, as below, I give
> them choices and then ask for an
> explanation of their answer.
>
> The first question on the exam was the following:
> A rock is thrown straight up from the Earth's surface.  Which one
> of the following statements
> concerning the net force acting on the rock at the top of its path
> is true?
> (a) The net force is instantaneously equal to zero newtons.
> (b) The net force is greater than the weight of the rock.
> (c) The net force is less than the weight of the rock, but greater
> than zero newtons.
> (d) The direction of the net force changes from up to down.
> (e) The net force is equal to the weight of the rock.
>
> The majority of students answered the question incorrectly.  Here
> is a sampling of some of the
> incorrect explanations:
>
> Student #1: choice a
> "The force pushing the rock up equals the force of gravity pulling
> it down so at the top its
> acceleration is zero and the net force is zero."
>
> Student #2: choice b
> "The net force is greater than the weight of the rock because in
> order for the force to push the
> rock up into the air, the net force has to be greater than the net
> weight."
>
> Student #3: choice a
> "At the top of the path at that instant both the velocity and
> acceleration of the rock is 0.  It is
> not until the rock starts its fall towards the ground that the net
> force downward is greater than
> the weight of the rock."
>
> Student #4: choice e
> "There is always an equal an opposite force acting on an object.
> Therefore the weight of the rock
> which is pulling it down is equal to the force upward."
>
> I can understand students' misunderstanding with regard to velocity
> being zero and acceleration not
> being zero, but I am amazed that students would think that some
> force other than gravity was acting
> on the object to make it move upward, even after it left the hand
> that threw it.  It very much
> reminded me of Aristotelian thinking.  Any comments?