From: Karen A. Mendelow (karenm@exploratorium.edu)
Date: Tue Feb 20 2001 - 16:16:47 PST
Message-Id: <l0313030cb6b8b8b35254@[192.174.2.171]> Date: Tue, 20 Feb 2001 16:16:47 -0800 From: "Karen A. Mendelow" <karenm@exploratorium.edu> Subject: Re: Pinhole Digest #586 - 02/17/01
Anu - The Exploratorium store has
"Cheshire Cat" - How we see the world
"Cool Hot Rod" - energy and matter
"Spinning Blackboard" _ Force and Motion
but it is all on line for free at www.exploratorium.edu
>Pinhole Digest #586 - Saturday, February 17, 2001
>
> large structure resonance(s)
> by <SFPhysics@aol.com>
> Light and color snackbook
> by <profradha@juno.com>
> Re: pinhole Light and color snackbook
> by "Deborah Hunt" <dhunt@exploratorium.edu>
> Learning Studio - week of February 11
> by "Gilles Poitras" <gilles@exploratorium.edu>
>
>
>----------------------------------------------------------------------
>
>Subject: large structure resonance(s)
>From: <SFPhysics@aol.com>
>Date: Fri, 16 Feb 2001 05:27:16 EST
>
>> My physics class is studying waves and we just looked at resonance and
>> watched the Tacoma Narrows bridge collapse. Students asked how we determine
>> the natural frequency of large objects (like bridges and buildings) to make
>> sure this doesn't happen again. I don't know the answer. help?
>> sally
>>>
>
>The real world natural frequency of large objects such as skyscrapers and
>bridges is determined via remote sensor accelerometers. Buildings like the
>TransAmerica Pyramid and the Golden Gate Bridge have remote accelerometers
>attached to various parts of the structure. When wind or an earthquake
>"excites" the building the accelerometers can detect the "ringing" (resonant
>oscillation) of the structure.
>
>The Golden Gate Bridge was "detuned" by having mass added at various points
>so that a standing wave of a particular frequency would affect only a small
>portion of the bridge. The Tacoma Narrows Bridge had the resonance extend
>the entire length of the span and only had a single traffic deck which could
>flex. The Golden Gate Bridge was modified after the Narrows Bridge collapse.
> The underside of the deck had stiffeners added to dampen torsion of the
>roadbed and energy absorbing struts were incorporated. Then mass additions
>broke up the ability of the standing wave to travel across the main cables
>because various sections were tuned to different oscillation frequencies.
>This is why sitting in your car waiting to pay the toll you can feel your car
>move up a down when a large truck goes by but the next large truck may not
>give you the same movement. That first truck traveling at just the right
>speed may excite the section you are on while a truck of different mass or
>one not traveling the same speed may not affect it much. As for the
>horizontal motion caused by the wind, the same differentiation of mass
>elements under the roadbed keeps the whole bridge from going resonant with
>Ĉolian oscillations.
>
>Just envision the classic Physics experiment where different length pendulums
>are hung from a common horizontal support. Measured periodic moving of the
>support will make only one pendulum swing depending on the period of the
>applied motion. If all the pendulums (pendulii?) had the same oscillation
>you could get quite a motion going with a small correctly timed force
>application. Bridges and buildings now rely on irregular distributions of
>mass to *help* keep the whole structure from moving as a unit that would
>result in destructive failure. Note also on the Golden Gate the secondary
>suspension cable "keepers" (spacers) are located at slightly irregular
>intervals to detune them. As current structural engineering progresses more
>modifications of the bridge will be done. The new super bridge in Japan has
>hydraulically movable weights that can act as active dampeners. What is
>earthquake (or wind) safe today will be substandard in the future.
>
>Al Sefl
>
>----------------------------------------------------------------------
>
>Subject: Light and color snackbook
>From: <profradha@juno.com>
>Date: Fri, 16 Feb 2001 12:06:46 -0800
>
>I am interested in Light and Color snackbook, but the online stores lists
>it as out of print. Does anybody have this book and would be willing to
>sell? Please email me with the price to <profradha@juno.com>
>Thanks a lot.
>
>
>Anuradha Dujari, Ed. D.
>Associate Professor
>Delaware State University
>Dover, DE 19901
>(302)857-6728, Fax 6722
>
>________________________________________________________________
>GET INTERNET ACCESS FROM JUNO!
>Juno offers FREE or PREMIUM Internet access for less!
>Join Juno today! For your FREE software, visit:
>http://dl.www.juno.com/get/tagj.
>
>----------------------------------------------------------------------
>
>Subject: Re: pinhole Light and color snackbook
>From: "Deborah Hunt" <dhunt@exploratorium.edu>
>Date: Fri, 16 Feb 2001 11:18:27 -0800 (PST)
>
>We hope to publish a new snack book sometime soon, but in the meantime,
>there are a couple of things you can do...
>1. try www.abebooks.com which is a clearinghouse for out-of-print books
>2. check out our online snacks at www.exploratorium.edu/snacks
>Deb
>
>On Fri, 16 Feb 2001 profradha@juno.com wrote:
>
>> I am interested in Light and Color snackbook, but the online stores lists
>> it as out of print. Does anybody have this book and would be willing to
>> sell? Please email me with the price to <profradha@juno.com>
>> Thanks a lot.
>>
>>
>> Anuradha Dujari, Ed. D.
>> Associate Professor
>> Delaware State University
>> Dover, DE 19901
>> (302)857-6728, Fax 6722
>>
>> ________________________________________________________________
>> GET INTERNET ACCESS FROM JUNO!
>> Juno offers FREE or PREMIUM Internet access for less!
>> Join Juno today! For your FREE software, visit:
>> http://dl.www.juno.com/get/tagj.
>>
>> ---------------------------------------------------------------------------
>>
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>>
>>
>
>
>---------------------------------------------------
>Deborah Hunt
>Internet Resource Specialist
>Exploratorium
>3601 Lyon Street
>San Francisco, CA 94123
>Voice: 415-353-0485
>Fax: 415-561-0370
>mailto:dhunt@exploratorium.edu
>
>"A woman is like a tea bag; she never knows how strong she is until she's
>in hot water." Eleanor Roosevelt
>
>
>
>----------------------------------------------------------------------
>
>Subject: Learning Studio - week of February 11
>From: "Gilles Poitras" <gilles@exploratorium.edu>
>Date: Fri, 16 Feb 2001 13:20:48 -0800
>
>This week we have bug related resources.
>
>In printed form:
>
>1. Insect musicians & cricket champions : a cultural history of singing
>insects in China and Japan / Lisa Gail Ryan
>SF 459 .C7 R9 1996
>
>2. Millions of monarchs, bunches of beetles : how bugs find strength in
>numbers / Gilbert Waldbauer.
>QL 496 .W36 2000
>
>
>Online (hopefully without bugs of a different sort):
>
>Several useful computer related books that are also available online.
>
>To locate the links for these works search our catalog for the titles.
> http://library.exploratorium.edu/
>
>1. Digital Imaging for Photographic Collections by Franziska S. Frey and
>James M. Reilly
>
>2. The United States Government Printing Office Style Manual 2000 by United
>States Government Printing Office
>
>3. The Mathematica Book by Stephen Wolfram
>
>4. Java: An Object Oriented Language by Michael A. Smith
>
>5. Palm Programming: The Developer's Guide by Neil Rhodes and Julie McKeehan
>
>6. Web Client Programming with Perl (first edition, 1997) by Clinton Wong
>
>7. The Java Tutorial by Mary Campione and Kathy Walrath
>
>8. Principles of Object-Oriented Programming in Java 1.1: The Practical
>Guide to Effective, Efficient Program Design by James W. Cooper
>
>9. Linux Network Administrator's Guide (second edition, 2000) by Olaf Kirch
>and Terry Dawson
>
>10. Linux Installation and Getting Started by Matt Welsh
>
>Gilles Poitras gilles@exploratorium.edu
>Learning Studio, Exploratorium Museum
>
>
>
>----------------------------------------------------------------------
>End of Pinhole Digest
>
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>To unsubscribe from pinhole, send an email to requests@exploratorium.edu
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>---------------------------------------------------------------------------
Karen Mendelow Nelson
Program Manager and Educator
Exploratorium Teacher Institute
3601 Lyon Street
San Francisco, CA 94123
karenm@exploratorium.edu
This archive was generated by hypermail 2b29 : Tue Oct 16 2001 - 12:22:16 PDT