Re: The sign of g

[Larry Smith <larry.smith@SNOW.EDU>]

At 9:12 PM -0400 9/3/02, Joe Heafner wrote:
> > From: Larry Smith <larry.smith@SNOW.EDU>
> >
> > Or is it the local gravitational field strength?
> I agree that it can be interpreted that way. In fact, I wish the
> textbook's did it that way to be consistent with the field approach in e&m.


Ahhh, it is more than a mere choice of words; what do we really _mean_ by
g?  And they don't have the same value; i.e. the acceleration of objects in
free-fall near the surface of the earth is not the same as the local
gravitational field vector.  The former is affected by the spinning earth,
the latter (in classical physics) is not.  The values of g in x = (1/2) g
t^2 and F (or W) = mg are not technically the same if the latter g is the
field strength.  And while the dimensions are the same, the units usually
reflect whether we are meaning an acceleration (m/s^2) or a field strength
(N/kg).

At 8:06 PM -0400 9/3/02, John S. Denker wrote:
> I wrote up a discussion of this at
>  http://www.monmouth.com/~jsd/physics/weight.htm

John makes the case that g (vector) is "the acceleration of a nearby
freely-falling object relative to your chosen reference frame" but I think
he is then not able to write F_g = mg, which many want to do parallel with
F_e = qE.

I'll repeat what I've said when we had this discussion before (definition
of weight): I don't care what convention we adopt, I just hope we all adopt
the same one.  And I'd like to know what it is so I can teach my students
consistently with the way y'all's students are being taught.

So what is g _really_?

Larry