Re: [Phys-l] vector inconsistencies

["Bob Sciamanda" <trebor@winbeam.com>]

> Suppose I have two classes, the 10:00 class and the 2:00 class.
> I show each of them a figure consisting of a bunch of vectors
> radiating from a point:
>   http://www.av8n.com/physics/img48/radiating.png
> and tell them this is in the context of geography i.e. topography.
>
> The question is, does this figure represent a peak or a pit?

It represents neither until you tell them what it is that you are 
illustrating.  Eg., the gradient of some scalar function of space,  the 
velocities of  a swarm of particles, etc.  (Indeed, you may be illustrating 
some spatial distribution of colors - according to some [hopefully 
expressed] convention.)  This is indeed what you say - further on.

The underlying point is that such graphical language does not follow some 
universal -written in stone- convention.  Its meaning must be (explicitly or 
implicitly) conveyed along with each application of such illustrations.

A drawn arrow merely indicates a direction,  The direction of WHAT is not 
inherent in the arrow - it must be an added piece of information.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.winbeam.com/~trebor/
trebor@winbeam.com