Re: Pendulum acceleration

[Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>]

Just my two cents...

When I saw the problem, I thought of 2-D net force (otherwise Tim wouldn't
have posted the question).  It isn't immediately obvious and since no one
has really answered the question, how about this: consider a pendulum that
is released when at an angle of 90 (i.e., horizontal):

          ---------0

When released its acceleration is initially g downward.

At the bottom, it has an acceleration of v2/r upward (not speeding up or
down).

            |
            |
            |
            |
            |
        <---0

The KE at bottom is related to the change in grav. pot. energy.  Compare
v2/r with g.

--------------------------------------------
Robert Cohen           rcohen@po-box.esu.edu
570-422-3428         http://www.esu.edu/~bbq
Department of Physics
East Stroudsburg University
East Stroudsburg, PA  18301
--------------------------------------------

> -----Original Message-----
> From: Tim O'Donnell [mailto:odonnt@CELINA.K12.OH.US]
> Sent: Wednesday, October 24, 2001 10:32 AM
> To: PHYS-L@lists.nau.edu
> Subject: Re: Pendulum acceleration
>
>
> Date sent:              Wed, 24 Oct 2001 08:35:53 -0400
> From:                   Tom Ford <tomford@THESCIENCESOURCE.COM>
> Subject:                Re: Pendulum acceleration
> To:                     PHYS-L@lists.nau.edu
> Send reply to:          "phys-l@lists.nau.edu: Forum for
> Physics Educators"
>         <PHYS-L@lists.nau.edu>
>
> > Tim,
> >
> > Use a liquid-filled accelerometer of the PSSC variety which
> > is mounted by two strings that will remain parallel as the
> > unit swings as a pendulum. Notice that the accelerometer
> > reads zero at the bottom and is a max (towards the
> > equilibrium position) at each extreme of the swing. The
> > accelerometer remains horizontal at all times. Then bring
> > the (bifilar) two strings together at the support. Notice
> > that now the accelerometer reads zero at all points of the
> > swing with the reading being taken tangent to the path. A
> > real classroom crowd-pleaser. This is much easier to
> > construct that making a curved air track with an
> > accelerometer on the glider (as was actually demonstrated
> > for me by the inventor of the popular form of air track,
> > John Stull).
> >
> > Tom Ford
> Tom,
> Thanks for this suggestion - this I can do.
> Thanks to all the others for their help.
> It seemed like an innocent enough question when I wrote
> it for my physics class for elementary teachers, but I see
> it is more complex then I first thought. I will discard this
> quetion on the test.
> Tim
> Tim O'Donnell
> Instructor of Physics and Chemistry
> Celina High School
> 715 East Wayne Street
> Celina, Ohio 45822
> (419) 586-8300 Ext 1200 or 1201
> odonnt@celina.k12.oh.us
>
> "Chance only favors the prepared mind." - Louis Pasteur