Re: speed and velocity

[Bob Sciamanda <trebor@VELOCITY.NET>]

Hi Brian,
I don't think we have a conceptual argument - only a language difference.
But in that vein, I would respond:
1) Since a vector is the sum of its components, those components must
also be vectors (apples and oranges).
2) I would accept calling the sign of a 1-d vector a "direction
indicator" instead of a subspace unit vector.

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor

-----Original Message-----
From: Brian McInnes <bmcinnes@PNC.COM.AU>
To: PHYS-L@LISTS.NAU.EDU <PHYS-L@LISTS.NAU.EDU>
Date: Thursday, November 26, 1998 1:54 AM
Subject: Re: speed and velocity


> Bob Sciamanda sent three interesting e-mails to the list earlier today.
>
> I have a problem with his definition of a one-dimensional vector as a
> component of a three-dimensional vector, carrying a sign for direction.
>
> As I understand it a component is obtained by a vector dot product and
is a
> scalar, not a vector.  the sign is not the direction of a vector but a
> consequence of whether the angle involved in obtaining the component is
less
> or greater than pi/2.  In particular, vectors do not have signs, they
have
> directions; they are intrinsically positive.
> What we can do (and this was the line that Tim Folkerts took as along)
is to
> associate the components with a unit vector along the special
one-dimension
> line.
>
> I agree that "mathematical models are our own constructs, subject to our
own
> definition and use" but
> it's preferable if we have common definitions and use.
>
> Brian McInnes