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Re: [Phys-l] Equations (causal relationship)



Good heavens! Brain disegaged. Sorry.
Apres moi les deluge.
Jack


On Tue, 2 May 2006, Jack Uretsky wrote:

Hi all-
Inarticulately, I guess, I tried to make the point that in
F=ma it is totally arbitrary as to which of the three variables is called a "caues", and which, if any, is called an "effect".
Apre' ma, les deluge.
Furthermore, the "deluge" demonstrates that the choice is strictly a
matter of taste and your faith in your understanding of the learning
process.
I guess it is therefore accurate to say that the discussion
is about faith-based teaching.
Regards,
Jack




On Tue, 2 May 2006, Rick Tarara wrote:

> 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
>
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