Re: N2

[John Barrer <forcejb@YAHOO.COM>]

   Assuming that students are already familiar with
the kinematics of linear acceleration as well as the
relationship between mass and weight (force of Earth
on an object), the modified Atwood requires very
little hand waving. In the "Modeling" approach, the MA
lab is at the start of the investigation of how force
relates to acceleration. Use of a Pasco lab cart on a
(level) lab table along with a low friction pulley to
change pull direction gives very good results. Keeping
system mass constant (means shifting masses from the
cart to the hanger) produces a very nice straight line
plot of acceleration vs. force whose slope is
1/(system mass). Or, keep the hanging mass (applied
force) constant and vary the load in the cart to
produce a straight line plot of acceleration vs.
inverse mass whose slope is the applied force (due to
hanging mass). Acceleration measurement is done with a
photogate and a "picket fence" on the Pasco cart. Note
that there is no need to measure the force applied to
the cart since we're dealing with the acceleration of
the SYSTEM (although you could so with a force probe -
but that's too much at the outset, IMHO.)
   In my experience, using the lab to develop the math
gives weaker (ie, most at the HS level) students a
much more effective way to learn the material compared
with algebra and force diagrams at the outset. John
Barrere
--- David Abineri <dabineri@CHOICE.NET> wrote:
> Thanks for the many comments and suggestions to my
> N2 question.
>
> Just to clarify, I am not against having my students
> analyze an Atwood
> type apparatus and they all do it after we have
> become comfortable with
> N2.
>
> My concern is, doesn't one have to use N2 to analyze
> an Atwood and
> therefore make such a lab experiment simply circular
> logic?  I was
> looking for a way to have them verify N2 without
> assuming N2 and do this
> early on in their exposure to N2.
>
> Thanks again for all the ideas.      Dave Abineri
>
>
> --
>  David Abineri   dabineri@choice.net


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