To move along the lines that John Clement has opened, a prime reason for
dealing with Forces as the cause of accelerations is in terms of the
(mis)conceptions/instincts with which the vast majority of students come
into physics. Straight from Aristotle they believe that all motion requires
a sustaining force along the direction of motion. Far too many will STILL
believe this upon leaving our courses.
That forces _cause_ accelerations then is a pretty important concept--forget
all the wrangling about commutivity, etc. That motion (velocity) does not
necessarily involve forces but rather changes in the motion (velocity) do,
is a difficult concept that can take considerable time and effort get
across. Using the equation a=net_F/m and the concept that the acceleration
of an object is caused by the vector sum of the forces acting on that object
seems to me to be all but essential to such instruction.
Of course, we shoot ourselves in the foot because of the wide-spread and
historical tendency to write F = ma (in all it's algebraic forms) instead
of net_F = ma (which we all of course understand, but which students
certainly do not). The algebraic logic some have been using to argue the
points of this thread are more valid with the latter form than with the
former, but for the novice (and perhaps terminal) physics student, the
concept of causation of accelerations due to forces is (as JC has reported)
a useful path towards a better Newtonian understanding of nature.
Rick
*********************************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, Indiana
rtarara@saintmarys.edu
********************************************************
Free Physics Educational Software (Win & Mac)
NEW: Updated animation packages.
COMING: Spanish language versions.
www.saintmarys.edu/~rtarara/software.html
Energy 2100--class project
www.saintmarys.edu/~rtarara/ENERGY_PROJECT/ENERGY2100.htm
********************************************************