Re: [Phys-l] Deceleration or Negative Acceleration

[ludwik kowalski <kowalskil@mail.montclair.edu>]

On Sep 9, 2008, at 4:44 PM, ludwik kowalski wrote:

> On Sep 9, 2008, at 2:01 PM, Steve Highland wrote:
>
> > > On 09/09/2008 07:02 AM, pschoch@nac.net wrote:
> > > > A student has asked which is
> > > > proper terminology: "Negative Acceleration" or "Deceleration".
> >
> > I agree with everything you have to say below.  What I'm wondering
> > about
> > is what is the best order in which to introduce these things to
> > students?
>
> One possibility is to begin with static equilibrium. The net force is
> zero and acceleration does not have to be mentioned. Introduce vectors
> and their components in that context. The preliminary unit of force
> could be pound.
>
> Then go to a=F/m, where the preliminary unit of acceleration is lb/kg.
> Then show that  the "official" unit of acceleration is m/s^2.


> Is  this a better alternative, in terms of teaching efficiency? This  
> would
> have to be tested.

How to introduce a=F/m? If the net force is zero that v=const. This is  
N1.
If F is not zero then v changes. That is where the concept of  
acceleration can be introduced, in the same way as in most textbooks.  
Direct proportionality between F and m -- this is N2 -- is introduced  
as an experimental fact (preferably via a lab activity).


Ludwik Kowalski, a retired physics teacher
5 Horizon Road, Apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/