Re: what to call little "g"

[Jim Green <JMGreen@sisna.com>]

John Gastineau has written a nice evenhanded question about the local
gravitational constant (sort of), g.  Let me try to give an evenhanded
responses: 

Calling g acceleration is evil, wicked, mean, bad, and nasty -- and it is
pedagogically dumb and terribly confusing to students and instructors alike.

It is NOT acceleration it is a local gravitational constant = GM/R^2.  It is
NOT on the ma side; it is on the F side of the equation!  This despite the
wishes of the Luddites and all extant texts.

There now that was evenhanded, wasn't it???  Or have we hit one of my four
physics nerves?

Jim Green  
Stamp out evil


At 03:29 PM 10/24/96 +0000, you wrote:
> I'm doing some editing for a publisher and have had a pet peeve of 
> mine disturbed one too many times, so please let me vent. I hope it's 
> constructive. 
>
> My peeve is the naming of little g as "the acceleration of (or due 
> to) gravity" Both phrases are wildly misleading. Using "of gravity" is 
> obviously a conceptual disaster since gravity is not accelerating. 
> However, saying "acceleration due to gravity" is very misleading 
> because there are lots of situations (like everything except airless 
> freefall) there the acceleration is not 9.8 m/s^2. 
>
> Ok. We can't use either common turn of phrase. What to use? The 
> problem is that there are two contexts for the use of g. One is 
> freefall, where g really becomes an acceleration. (I prefer using 
> a(sub)g instead, but that's another story.) Let us name the case were 
> g should be an acceleration "freefall acceleration." 
>
> The other context is in discussing force, eg, W=mg. It always blows
> away my students when I point out that g is not an acceleration
> here. (In most elementary problems where this first comes up the
> mass is at rest! there's clearly no acceleration.) It is the local
> gravitational constant which has units Newtons/kilogram. Thus, I name 
> g in this context  the "local gravitational constant." 
>
> (aside: to say that N/kg is the same thing conceptually as m/s^2 is
> to agree that torque can be expressed in Joules (N-m). We on phys-l
> went through all of that not long ago.)
>
> Changing established usage is an uphill  battle. But, in physics we
> are sticklers for detail (we have to be) so I believe usage is
> important. Do any of the rest  of you agree? Is there a better
> choice of phrases? "Local gravitational constant" won't mean much to
> many people, I'd bet. What can be done to improve the clarity of the
> discussions in introductory physics regarding "g"?
>
> JEG
>
> PS My next tirade will be on usage like "the tension overcomes the 
> frictional force" or worse, "gravity overcomes friction..." 
> ==================
> John E. Gastineau
> 304 296 1966
> Morgantown, WV 
> http://www.badgerden.com/~gastineau
> email: gastineau@badgerden.com   <==== NEW as of 10/1/96