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Re: force



Joseph Bellina wrote:

On Thu, 31 Oct 1996, Roger A. Pruitt wrote:
To a physicist, both acceleration and force are real observable
quantities, however, I think that of the two that acceleration is the
more abstract.

I would suggest that force is experienced, but not observed, whereas
acceleration is observed, but not experienced...and therein lies part of
the problem. Force is a real ghost in the machine for physics...when
push comes to shore (heh..heh), we really know what it is.
Roger, what do you think it is?

cheers

Joe

Roger Pruitt,

Joe, I agree in general with everything you said. However, I often think
that we nitpic too much on this list. I include myself as I have risen
to the bait and commented on current flow, heat, g, and now force and
acceleration. Gene Mosca noted that we observe deformations--not forces.
At one level this is certainly correct. A sensor has to deform in order
to produce a signal that will indicate a force. Even when I push on the
desk with my hand, I am producing a deformation in the nerve cells in my
hand that indicate that I am applying a force. At this level, you are
also correct to say that we experience the force--not observe it. I was
using the more general expression, universal in physics, that we observe
it, and not meaning by "observe" that we see it.

In this sense we observe both accelerations and forces. However, I still
maintain that forces are easier to observe, and even the qualitative
"measurement" (estimate) of a force is more direct that making a
qualitative "measurement" of an acceleration. The later involves too
many indirect steps and mental computations as I pointed out in a
previous comment.

Well, there's lots of reasons for nit picking...

It seems to me that when we obscure distinctions between observation and
either hypothesis or explanation, then we run the serious risk of "tunnel
vision" in our thinking...something I thought physicists generally are
proud to suggest they are "free" of.

It seems to me the crucial issue for physics teaching here is that if
"force" is a non-unique construct derived from experience, yet, we talk as
if, and "teach" as if, it is unique and observable, then an elemental and
easy to generate prediction is that students will have a hard time with it.
Lo and behold, they do! Might'nt this then be a nit which not picked
leaves us in a less than desirable state of "teaching"?

Incidently, Roger Haar has taken some criticism from others for comments
made by me. Roger, please accept my appology, and I hope that other
readers went back and reread the header and realized that you are not to
be blamed for my ideas.

To Roger Haar, my apologies too...since I was the one who mistakenly used
your name.
Dewey


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Dewey I. Dykstra, Jr. Phone: (208)385-3105
Professor of Physics Dept: (208)385-3775
Department of Physics/SN318 Fax: (208)385-4330
Boise State University dykstrad@varney.idbsu.edu
1910 University Drive Boise Highlanders
Boise, ID 83725-1570 novice piper
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