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Re: [Phys-l] Deceleration or Negative Acceleration




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/