Re: [Phys-l] Weight?

["Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>]

Isn't UMPERG's comments related more to the units to use?

I couldn't quickly find the spot on their web pages and we have you as a resource;  does UMPERG equate numerically g and a_g?

_________________________

Joel Rauber, Ph.D 
Professor and Head of Physics
Department of Physics
South Dakota State University
Brookings, SD 57007
Joel.Rauber@sdstate.edu 
605.688.5428 (w)
605.688.5878 (fax) 

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of John Clement
> Sent: Wednesday, November 17, 2010 1:02 PM
> To: 'Forum for Physics Educators'
> Subject: Re: [Phys-l] Weight?
>
> According to the UMPERG group g should be defined as 9.81 N/kg on the
> surface of the Earth if it is used in the equation F_g=mg.  This is
> because
> they have found that g=9.81 m/s^2 is extremely confusing to students.  I
> can
> remember thinking as a student it is stupid to calculate F_g = m x 9.81
> m/s^2 for an object which is at rest because it is not accelerating.
> Also
> unit conversions are often just incantations.  So the proposed
> formulation
> makes more sense to students.  The idea that N=kg m/s^2 is a very
> foreign
> incantation to them.
>
> I would use a_g to notate the free fall acceleration.  Again this is
> inline
> with the idea that all accelerations should be notated a, all forces F,
> all
> energies E, with appropriate subscripts.  The separate symbols for the
> same
> type of quantity make students think they are different things, and
> serve as
> a barrier to integrated thinking.
>
> I am not claiming it is "truth" or "correct" merely that research points
> to
> it being pedagogically better.  You are free to disagree, but if you
> want
> evidence go to the UMPERG web page and their various papers.
>
> The big problem is that the vast majority of intro physics students in
> an
> algebra based course do not have proportional thinking.  So many things
> become incantations rather than understood concepts.  Many of them
> exhibit
> the characteristics of concrete operational thinking so multiple steps
> are
> extremely hard.  Three variable equations such as a=F_net/m are opaque
> and
> have no meaning to them.  Shayer & Adey's "Really Raising Standards" has
> good information on this problem.
>
> All too often the debate is really about what "is is".
>
> John M. Clement
> Houston, TX
>
>
> > Quick question:  You say that mg is the pull of gravity, I'm gathering
> > from what you said below you mean the integrated contribution of all
> mass
> > elements constituting the earth.  Does that mean that g is not the
> free-
> > fall acceleration of an object?
>
>
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