Re: Kinematics First

[John Clement <clement@HAL-PC.ORG>]

OK, after looking at your presentation, force first sounds like it is a well
thought out idea, but you will not know how well it works until it has been
tried and tested for gain on the FCI/FMCE.  While not perfect these are the
baseline tests.

I am not sure that the force first sequence is suitable for students who
think at the concrete operational level or even the transitional level.
Many of my students have some really severe problems with the idea of change
in a quantity.  If the quantity is position it is somewhat manageable.  If
change in a more complicated quantity such as momentum is introduced early
it might pose a severe barrier.  The fact that momentum involves 3 variables
means that it is difficult for students who are not at the formal
operational level.  One of the very simple problems is that they habitually
calculate change in a quantity by subtracting the second number from the
first rather than the earlier quantity from the later one.  This is clearly
a reflection of the early training where the bottom number is always
subtracted from the top one.  Sometimes they will even say it correctly, and
then key it in wrong.  While the FCI/FMCE appear to be excellent diagnostics
it is evident that there are many other "misconceptions" such as position,
calculational, reference frames ... that are not tested by them.  An
interesting example of reference frame misconceptions is that students will
say that a car going around a circular track has not change in velocity
because it is always going foreword, or when they see something falling off
of a car which is accelerating to the left that the object goes to the right
even when you draw a line through the object on the TV screen and it lands
to the left of the line.  A calculational problem which is also an inability
to be specific is the way they calculate V=distance/time rather than V=Dd/Dt
(D meaning delta).  This problem is partially because they memorized the
first formula in a physical science or math course.  This latter problem is
easily revealed if they have to generate a velocity graph from a strobe or
motion diagram (series of pictures at equal time intervals of a moving
object).  Incidentally some students can not tell me the sign of position
from a picture of a car on a number line with the origin clearly marked to
the right of the car and the positive and - sides of the axes marked.  I
even have HS seniors who ask what "sign" means.

One reason for kinematics first is that you really need to do velocity &
position first if you wish to then do momentum.  Then doing acceleration &
velocity next exposes students to the similarity between v,x and a,v.  It
also lets you hit some of the calculational problems heavily.

John M. Clement


> I forgot to mention that an outline of my "Force First" program was
> presented at the January 1997 AAPT meeting and is online at
>
>   http://www.csupomona.edu/~ajm/professional/talks/forcefirst.pdf
>
> John
> --
>     A. John Mallinckrodt        http://www.csupomona.edu/~ajm
>     Professor of Physics      mailto:ajm@csupomona.edu
>     Physics Department         voice:909-869-4054
>     Cal Poly Pomona              fax:909-869-5090
>     Pomona, CA 91768-4031     office:Building 8, Room 223