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John S. Denker said (Fri 11/14/2003 9:51 AM):
" 3) Cause should precede effect. The force F does
not precede the acceleration a=3DF/m ... they must
both happen at the same time."
I am not aware of the condition that a cause has to
precede its effect. Can anyone provide evidence that
the word "cause" necessarily implies precedence?
Robert argues that some students believe that a
cause must precede its effect, and that saying that
the net force causes acceleration confuses these
students. Even if "cause" does not necessarily
imply precedence, we should be careful in the use
of the word "cause" if it confuses students.
I would prefer to emphasize that although the
net force causes the acceleration, the net force
does not precede the acceleration.
John and others advocate not using the word
"cause" at all in this context. However, if
"cause" does not necessarily imply precedence,
I would discourage people from stating that the
net force does not cause the acceleration.
Daniel Crowe
Oklahoma School of Science and Mathematics
Ardmore Regional Center
dcrowe@sotc.org
-----Original Message-----
=46rom: Robert Cohen [mailto:Robert.Cohen@PO-BOX.ESU.EDU]
Sent: Friday, November 14, 2003 11:13 AM
To: PHYS-L@lists.nau.edu
Subject: Re: Causation in Physics: F=3Dma
As I've mentioned before on this topic, my problem with "force
causing acceleration" is that it implies a time delay in some
students' minds, reinforcing their belief that acceleration and
velocity are the same thing. In other words, the following is
the thinking of the students:
A force causes the object to have a velocity it didn't have
before. This means that you apply a force and eventually the
object has the new velocity. It may take time, but eventually
the object attains this new velocity. It is this "new velocity"
that is "caused" by the force.
You can use "acceleration" if you'd like but they'll continue
to think "velocity" until they see both happening at the same
time. And the word "cause" doesn't help make things clearer
for them.
____________________________________________________
Robert Cohen; 570-422-3428; www.esu.edu/~bbq
East Stroudsburg University; E. Stroudsburg, PA 18301