Re: [Phys-l] F causing a or Delta-V causing I

["Robert Cohen" <Robert.Cohen@po-box.esu.edu>]

I had written:
> Thus, it is clear that current through the element causes a voltage 
> across it (Delta V=IR) and not the other way around.  :)

to which John Denker responded:
> Sorry, that's not clear at all.

And I'm sorry I wasn't more clear.  I wasn't serious when I said "not
the other way around".

<snip>
> Therefore, if you believe in proof-by-example, it must be 
> "clear" that the equation V = I R should be interpreted as a 
> statement that R causes V.

I suppose I should've used that language instead of the ambiguous smiley
face.  So, for completeness, this is what I should have written:

Therefore, if you believe in proof-by-example, it must be "clear" that
the equation V = I R should be interpreted as a statement that I causes
V. (can I still add a smiley face?)

To get back to the original discussion, it is important to recognize (as
Jack Uretsky pointed out a while ago) the difference between writing an
equation that reflects the dependent/independent variables and writing
an equation that represents "cause/effect".  My point is: just because
you can "control" R does not mean that R "causes" V.  

____________________________________________________
Robert Cohen, Chair, Department of Physics
East Stroudsburg University; E. Stroudsburg, PA 18301
570-422-3428; www.esu.edu/~bbq