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

[Ludwik Kowalski <kowalskil@mail.montclair.edu>]

On Sep 17, 2007, at 9:34 AM, Rauber, Joel wrote:

> 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?
>
> They haven't been introduced to the Newton or force as of yet.
>
> I can think of some possibilities (in random order)
>
> 1) use m/s^2 as has been traditionally the case, ignoring the PER
> comment post
>
> 2) use m/s^2 while doing kinematics and then switch to N/kg when I 
> start
> dynamics.
>
> 3) use N/kg from the beginning and just tell the students that it
> equates to m/s^2, but not writing it that and basically not worrying
> about any confusion that the use of the N unit would cause since we 
> will
> be getting pretty quickly to dynamics.
>
> Any advice or comments?

My approach was to define new units in terms of basic units only, which 
are kg, m and s. The unit of force, N, is not basic. That is why N/kg 
is only an abbreviation, as far as the unit of acceleration is 
concerned.
_______________________________________________________
Ludwik Kowalski, a retired physicist
5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/