Re: transfer of momentum

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

BUT......

The important feature here is when the momentum changes.  How do you know
when the momentum changes?  Answer--if the object speeds up, slows down, or
changes direction.

Now if using acceleration, one asks:  "How do you know if the object is
accelerating?"  Answer--if the object speeds up, slows down, or changes
direction.

I can't see that one approach is any different (or easier) than the other.

(The velocity (or momentum) versus time graph for the vertically thrown ball
makes things crystal clear--for us, but unfortunately not for the
students--especially gen-ed students.  Been doing this for a couple of
decades now!)

Rick

*********************************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, Indiana
rtarara@saintmarys.edu
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********************************************************
----- Original Message -----
From: "Chuck Britton" <britton@NCSSM.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, November 19, 2003 10:36 AM
Subject: Re: transfer of momentum


> If I understand John correctly -
>
> He is trying to DOWNplay the equation that most of us rattle off as N2,
F=ma.
> A MUCH better representation of Force is Newton's own version
>
>         F = delta p/delta t
>
> Even for those intro students who are being introduced to SR (or GR),
> it is VERY good pedagogy to use the momentum formalism in favor of
> the acceleration approach.
>
> Most of us realize how much trouble acceleration causes for our students.
>
>         Example - a ball at the top of it's trajectory. What is the
> force/acceleration of the ball AT THAT INSTANT!!!
>
> If you think that most of your student 'get this' you are sadly mistaken.
>
> Drawing a momentum vs time graph (or more commonly,velocity vs time)
>
> Gives them a visual picture that answer the difficulty for some/many
students.
> Acceleration is a VERY difficulty concept.
>
> Momentum is a MUCH simpler and basic concept.
>
> USE it ! ! ! !
>
> OK, ya'll, at 9:56 AM -0500 11/19/03, Bob Sciamanda wrote:
> >  I respect your free choice to use this conceptual model of F=ma in
> >  component form.  As with all conceptual models, this is a matter of
> > taste and free choice;  the testable physics lies in the quantitative
> >  relations connecting measurables.
>
> --
> Chuck Britton                                   Education is what is left
when
> britton@ncssm.edu                       you have forgotten everything
> North Carolina School of Science & Math         you learned in school.
> (919) 416-2762                                  Albert Einstein,
1936