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Re: force



Joe,

Can you be more explicit about your contention that acceleration is
somehow "more observable" than force? Qualitatively we may be able to
"directly perceive" an object changing its state of motion, but it seems
to me that "observing" acceleration in any quantitative fashion requires
a large number of pretty complicated calculational steps that take you a
long way beyond the required measurements of position and time. Frankly,
I don't see that the force exerted on your hand by a compressed spring is
any less directly perceptible than acceleration and I might even argue
that it is more so. It certainly offers a more visceral impression. And
it's far simpler to attach a quantitative value to that force through the
measurement of how far the spring compresses and a simple procedure that
establishes its relative stiffness.

John
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A. John Mallinckrodt email: mallinckrodt@csupomona.edu

John, sure a force on oneself is perceptible, but is the force on another
object perceptible? I think the only way we 'perceive' such a force is by
inference and *not* the direct perception of the force itself. Even your
example illustrates this. Is the acceleration of an object more
perceptible than the forces on it? I think that people can come to notice
acceleration, with practice even to the point of making good estimates of
its magnitude. This isn't often done to this extent, but I do see students
start their study of motion exhibiting no evidence of even noticing
acceleration and leaving their study showing distinct evidence of noticig
acceleration. *But* I do not see how anyone can directly perceive a force,
itself, which we take to be exerted on another object.

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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