Re: Newton's Second Law

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

PROGRESS REPORT 1

We eliminated the "dynamical" accelerometer
and measured the a(t) with the motion detector.
Works great too!

The forcemeter is stationary. A very thin
thread, about 1 m long, is attached to it.
The other end of this thread is attached
to a rubber band which is attached to a
cart. The cart can roll (with minimal
friction) along a flat surface toward the
motion detection probe. We measure F(t)
and d(t) 40 times per second; a(t) is
calulated from distances.

The mass of the cart was 745 grams, the
maximum force 5 N. The slope of the F=f(a)
curve is very close to m. Work is in
progress. I am doing this with two high
school teachers; John Gastineau is
directing us. We want to explore several
methods of measuring accelerations and
see which one is the best. Perhaps this
will be turned into a TPT note. It seems
to be a good topic for student project.

Work in progress, Ludwik Kowalski



> I enjoyed the comments made by Ludwik Kowalski and John Denker
relative
> to my original question about N2.
>
> I am sure that the graphs of F and a that Ludwik saw were great BUT
I am
> always trying to look at such graphs from the beginning student's
point
> of view, someone who has just seen N2 and is beginning to grapple
with
> its implications.
>
> I see two concerns from this point of view. The first was mentioned
by
> John is that an accelerometer of this type is using N2 to measure
> acceleration so we have circular logic.  The second is that an
> accelerometer must have very little meaning to a beginning student.
I
> would much rather that a beginner see a plot of v vs t and
understand
> that a is the slope.  I think we have to be cautious about using
> equipment that tends to hide the fundamental quantities that we want
> beginners to understand well.
>
> Certainly measuring the force directly is an advantage in N2 but my
> original question was posed because an air track cannot support a
force
> sensor (not the ones we have anyway) and so I was looking for other
ways
> to establish the force.
>
> Thanks for all the great comments on this topic.      Dave Abineri
>
>
> --
>  David Abineri   dabineri@choice.net