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



Hi all-
There seems to be general agreement that a "causal" relationship
between physical quantities implies a time lapse between the quantities
(except for one unfortunate circular definition of "causal"). Such a
definition (as J.D. has aptly pointed out) would violate the symmetry
implied by an equality relationship between the quantities. So I propose
an alternate definition of "causal relationship".
Students are taught, in connection with lessons on graphing, to
distinguish between dependent and independent variables. In the context
of physics we can, and often do, choose an independent variable to be one
over which we have control in a given experiment. In that context I am
free to speak of the independent variable as "causing" the "response" of
the dependent variable. This usage only involves arbitrary naming that
does not violate the symmetry of an equality between physical quantities,
and only has implication concerning the setup of experiments.
In this context I like F=ma because it is easy to conttrol forces,
but difficult to create accelerations without applying forces. Also, this
my definition permits me to say, without cuasing great discomfort to
knowledgeable listeners, that force "causes" acceleration.
Regards,
Jack


On Sun, 30 Apr 2006, John Denker wrote:

Larry Smith asked:

>> Would you agree there is a cause and effect relationship here?

I have a book on my desk which says ...

This is such a lame appeal to authority that I assume LS is being
facetious ... damning with faint praise.


Bernard Cleyet wrote:

Does the lack of reply mean there is universal agreement?

Think about it.

Give two (independent!) good reasons why Ohm's law must not be
considered a statement of cause-and-effect.

============================

More generally: Silence never implies assent. The more facetious or
preposterous the remark, the less it deserves to be commented on. We
should be discussing the best ideas in the community, not the worst.

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