Re: N/kg versus m/s^2

["Prof. John P. Ertel (wizard)" <jpe@USNA.EDU>]

I've resisted jumping into this fray because I could not see anything
useful coming out of the discussions.

On the other hand, I now think I can see something that is negative coming
out of the discussion.

In a recent reply to the thread
On Thu, 25 Jan 2001, John Denker wrote:
...
> > At 08:28 PM 1/25/01 -0600, John M. Clement wrote:
> >
> > > Under the more rational treatment g is then stated as being 9.8N/kg at the
> > > surface of the earth, not 9.8m/s^2.
According to physics as I understand it, 9.8N/kg is formally identical to
9.8m/s^2.  The foregoing attempts to create a distinction without a
difference.  Calling it "the more rational approach" doesn't make it
rational.

+=================================+

Here I have to take exception!  Yes, 9.8N/kg is technically equal to
9.8m/s^2 but I would strongly suggest that they are not identical in
information content.  Using g=9.8m/s^2 and the words "acceleration due to
gravity" is almost guaranteed to evoke a wrong mental picture or
association in the minds of at least our introductory students which may
hang on into later classes.  OTOH: Using g=9.8N/kg has two positive things
going for it:

1) it steps around the confusion that is rampant among our students about
"acceleration due to gravity", and
2) conveys a strong analogy to the unit for electric field  N/C.

After all, would we would never say (or would we?) that because the
product of the force unit with the length unit is technically equivalent
to the energy unit (Nm=J) that it would be OK to measure/quote the results
of a calculation of torque in units of Joules.  Even if there is a unit
equivalence here, it is at least misleading and I think just plain wrong!

Just one person's opinion of course.

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