Date: Tue, 12 Dec 2000 11:20:44 -0700

Author: Jim Krider

Subject: RE: Hoberman Sphere and Conservation of L

Post:

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Has anyone given this demo a PIRA DCS number yet? I was thinking of 1Q40.75
thinking it is spherical like the Hero's engine. Or 1Q40.19 after the
rotating stool but before the Squeezatron.

Bill, you should submit this marvelous demo to The Physics Teacher so that
it will be published and have an official PIRA DCS number.

Jim
******************************************
Jim Krider James.Krider@asu.edu
Physics and Astronomy Instructional Resource Team
Arizona State University Department of Physics and Astronomy
PO Box 871504, Bldg. PS Rm. F470,Tempe, Arizona 85287-1504
Phone: 480-965-8086 FAX: 480-965-7954 Web:
http://www.public.asu.edu/~jkrider/



-----Original Message-----
From: William W. McNairy [mailto:mcnairy@phy.duke.edu]
Sent: Tuesday, October 17, 2000 1:04 PM
To: tap-l@listproc.appstate.edu
Subject: Hoberman Sphere and Conservation of L




Greetings Tappers--

At the suggestion of a prof in our introductory physics for pre-med course,
we just constructed an attractive conservation of angular momentum
demo. Take one (large) Hoberman sphere (see Zany Brainy or other
children's store). As per enclosed instructions, insert the pulley
connections into the sphere.

With carpenter's string (braided, about 200 lb test), tie the pulley to a
ball bearing swivel. This was also a hint from the (angler) professor--
these swivels available from WalMart fishing area for about $1.50/3-- works
much better than traditional brass swivel. Tie the swivel to more string
and loop the other end of the string through the hook you have in the
ceiling for the bowling ball pendulum. If you don't have the hook in the
ceiling for the pendulum, you should. Install one now.

Adjust the height of the sphere to a comfortable level for the prof. Spin
the fully extended sphere-- then pull on the cord passing over the pulley
to force the Hoberman sphere to collapse. Angular velocity increases
rapidly as the sphere collapses to very small size (decrease in moment of
inertia). Let out the cord to have the sphere enlarge again-- it
slows. Repeat this process.

Students ooohed and aahhed over this one-- pretty sphere, pretty spinning.

Hoberman spheres available in a variety of colors, including glow in the
dark models.

Enjoy!

bill

*****************************************
William W. McNairy, Ph. D.
Senior Lecturing Fellow
Room 104I (919)-660-2689
Dept. of Physics, Duke University
Box 90305 Durham, NC 27708
*****************************************

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charset=3Diso-8859-1">
5.5.2653.12">
RE: Hoberman Sphere and Conservation of L



Has anyone given this demo a PIRA DCS number =
yet?  I was thinking of 1Q40.75 thinking it is spherical like the =
Hero's engine.  Or 1Q40.19 after the rotating stool but before the =
Squeezatron.



Bill, you should submit this marvelous demo to The =
Physics Teacher so that it will be published and have an official PIRA =
DCS number.



Jim

******************************************

Jim =
Krider           =
            =
     James.Krider@asu.edu


Physics and Astronomy Instructional Resource Team =


Arizona State University Department of Physics and =
Astronomy


PO Box 871504, Bldg. PS Rm. F470,Tempe, Arizona =
85287-1504


Phone: 480-965-8086   FAX: =
480-965-7954   Web: HREF=3D"http://www.public.asu.edu/~jkrider/" =
TARGET=3D"_blank">http://www.public.asu.edu/~jkrider/







-----Original Message-----

From: William W. McNairy [ HREF=3D"mailto:mcnairy@phy.duke.edu">mailto:mcnairy@phy.duke.edu] ONT>

Sent: Tuesday, October 17, 2000 1:04 PM

To: tap-l@listproc.appstate.edu

Subject: Hoberman Sphere and Conservation of =
L









Greetings Tappers--



At the suggestion of a prof in our introductory =
physics for pre-med course,


we just constructed an attractive conservation of =
angular momentum


demo.  Take one (large) Hoberman sphere (see =
Zany Brainy or other


children's store).  As per enclosed =
instructions, insert the pulley


connections into the sphere.



With carpenter's string (braided, about 200 lb test), =
tie the pulley to a


ball bearing swivel.  This was also a hint from =
the (angler) professor--


these swivels available from WalMart fishing area =
for about $1.50/3-- works


much better than traditional brass swivel.  Tie =
the swivel to more string


and loop the other end of the string through the =
hook you have in the


ceiling for the bowling ball pendulum.  If you =
don't have the hook in the


ceiling for the pendulum, you should.  Install =
one now.



Adjust the height of the sphere to a comfortable =
level for the prof.  Spin


the fully extended sphere-- then pull on the cord =
passing over the pulley


to force the Hoberman sphere to collapse. Angular =
velocity increases


rapidly as the sphere collapses to very small size =
(decrease in moment of


inertia).  Let out the cord to have the sphere =
enlarge again-- it


slows.  Repeat this process.



Students ooohed and aahhed over this one-- pretty =
sphere, pretty spinning.



Hoberman spheres available in a variety of colors, =
including glow in the


dark models.



Enjoy!



bill



*****************************************

William W. McNairy, Ph. D.

Senior Lecturing Fellow

Room 104I  (919)-660-2689

Dept. of Physics, Duke University

Box 90305  Durham, NC 27708

*****************************************




=

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