Re: [Phys-l] PER folks and units of g

[Rick Tarara <rtarara@saintmarys.edu>]

I would think the problem here would go away if nobody used 'g' as the 
acceleration due to gravity.  When we do kinematics, I don't allow equations 
that start out with a 'g' in them.  Rather we identify the acceleration (a) 
as about 10 m/s^2 down.  The only loss (and I don't consider it large) would 
be that we shouldn't really use the Range equation R = (v^2)sin92theta)/g --  
but with it's use so limited, I try to avoid it in favor of working out any 
2-D motion from first principles.

OTOH, we could also reserve 'g' as the acceleration due to gravity (with 
acceleration units), and always use script-G for the gravitational field. 
But that would require we write Weight = mG  rather than mg.

So--use 'g' only as the field (N/kg) or only as an acceleration.

Rick

----- Original Message ----- 
From: "Ken Fox" <physicsfox23@gmail.com>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Monday, September 17, 2007 10:15 AM
Subject: Re: [Phys-l] PER folks and units of g


> I agree with Jeffrey's as the best solution. In my mind there is a huge
> conceptual difference between a(g) and g. It is a wonderful point of 
> nature
> that they are numerically equal and even the units are equivalent (pun
> intended). I tweak the brain by indicating that one day they will 
> appreciate
> this coincidence.
>
> ma(g) = mg   two concepts of mass are at work here as well.
>
> One hard thing about this is conflicting with the text book or web
> resources.
>
> Ken Fox
>
> On 9/17/07, Jeffrey Schnick <JSchnick@anselm.edu> wrote:
> > I use a_g = 9.8 m/s^2 for the acceleration of an object in freefall near
> > the surface of the earth and g = 9.8 N/kg for the magnitude of the
> > earth's near-surface gravitational field.
> >
> > > -----Original Message-----
> > > From: phys-l-bounces@carnot.physics.buffalo.edu
> > > [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf
> > > Of Rauber, Joel
> > > Sent: Monday, September 17, 2007 9:34 AM
> > > To: phys-l@carnot.physics.buffalo.edu
> > > Subject: [Phys-l] PER folks and units of g
> > >
> > > This is mostly addressed to the PER gurus, but others should
> > > need no invitation to chime in, as their experience is
> > > appreciated and valuable.
> > >
> > > There was a post a while back that suggested that the PER
> > > research was indicating that it is best to quote g as follows:
> > >
> > > g = 9.8 N/kg rather than g = 9.8 m/s^2
> > >
> > >
> > > the question I have is following a traditional sequence of
> > > kinematics first, while introducing free-fall what do you
> > > suggest for g?
> > >
> > ...
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