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Re: displacement and graphs



----- Original Message -----
From: "John Mallinckrodt" <ajmallinckro@CSUPOMONA.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, October 10, 2001 8:41 AM
Subject: Re: displacement and graphs


On Wed, 10 Oct 2001, Rick Tarara wrote:

The position is not a vector, only the change in position

How can the change in something that is *not* a vector magically
*become* a vector? Isn't "change in position" is just a shorthand
for "change in the position vector", i.e., r2_vec - r1_vec?

Perhaps we need to more carefully distinguish between

"location" = "a point in space"

and

"position" = "a vector locating a point in space relative to some
other arbitrary, clearly identified, and "fixed" (whatever that
means!) point in space."

Seems to me that we do--we tend to call your 'location' -- position, and
your 'position' --displacement. Agreed that the language is sloppy, but it
is _very_ widespread. 'Location' also implies (at least to me) a location
relative to some reference. Therefore I'm not sure it is any better than
'position' in removing the implied vector nature of the beast. It would
seem that 'displacement' is the term we've created to explicitly contain the
vector nature. To get away from your first objection (if P is not a vector
how can delta-P be one) then we probably should ONLY talk about
displacement, but students are going to think in 'location' or 'position'.

Rick