Re: counting balls

[trappe@PHYSICS.UTEXAS.EDU (Karl Trappe)]

PIRA (Physics Instructional Resource Association, an afiliate society of
AAPT) has been classifying demonstrations for ten years now under a Dewey
Decimal-like numbering system called the PIRA DCS (Demonstration
Classification Scheme).  Under the leadership of the late Phil Johnson of
Minnesota, we classified over 7500 physics demonstrations/references,
including many of the TPT and  AJP demonstration related articles.

In this numbering system, 1N30.xx corresponds to collisions in one
dimension.  1N30.10 is "collision balls", the generic (universal PIRA) name
for the demonstration you mentioned.  It consists of six billiard balls
mounted on bifilar supports.   Among the references deemed "similar" and
given the same number are: 9-5.3 (from Meiners, which describes eleven
billiard balls on bifilar suspension), M-15a.1 (from Hilton, which
describes two balls, five balls, six balls on bifilar suspension), Disc
05-01 (from the Video Encyclopedia of Physics Demonstrations which shows
two balls of equal mass collide, then balls of various mass ratios are
used.  Collisions with a string of equal balls are also demonstrated), and
AJP 30(10), 767 (an AJP article using croquet balls with the warning to
weigh the balls at the store to get nearly eequal masses).

If you want to see slight modifications, 1N30.11 describes a large frame
holding seven bowling balls.  1N30.12 describes two collision balls in
bifilar support, 1N30.13 describes a two ball apparatus for the overhead
projector.  1N30.14 discusses the theory of collision balls.  1N30.15 lists
collision balls rolling on a track for guidance.  1N30.16 uses Duckpin
balls.

AND...1N30.20 (the next main subdivision of the numbering system) begins
the 3:1 mass ratio collision balls. This continues with variations until
the *next* main subdivision 1N30.30 which is air track collisions with
gliders.  And continuing on with modifications until 1N30.50, the bouncing
dart...to 1N30.60, the double ball drop with many of its modifications...to
1N30.70, colliding cylinders.  There's room for several more "important"
main subdivisions to be added (1N30.80, 1N30.90).  Now, 1N40.xx begins
collisions in *two* dimensions...

And yes, AAPT is considering publishing the work...Makes your mouth water!
Enjoy, Karl

> > > > [question asked from the list:]
> > > > 1. What is the "counting ball demo"?
> > >
> > > The counting balls are those lines of five ball bearings suspended
> > from  two rails. Pull n balls off one side (n<5) and realease them, n
> > balls are ejected from the other side after the first n balls collide.
>
> > I think this is also called the "Newtonian Demonstrator" or the
> > "swinging balls" demonstration.
>
> > Steven Ratliff
>
> The boys in my physics classes always referred to this apparatus as
> "Newton's Balls".  This name always got a rise out of the more
> modest girls in the class.
>
> Herb Gottlieb from New York City
> (Where the boys in ou physics classes usually outnumber the girls)

Dr. Karl I. Trappe                              Desk Phone:  (512) 471-4152
Physics Dept, Mail Stop C-1600                  Demo Office: (512) 471-5411
The University of Texas at Austin               Home Phone:  (512) 264-1616
Austin, Texas 78712-1081