From: Deborah Hunt (dhunt@exploratorium.edu)
Date: Thu Apr 22 2004 - 10:22:10 PDT
Message-Id: <a05111b0bbcadaf9a5b42@[192.174.2.158]> Date: Thu, 22 Apr 2004 10:22:10 -0700 From: Deborah Hunt <dhunt@exploratorium.edu> Subject: Re: autompbile window polarization splotches
Jeff, that also reminds me that we have a Snack online that shows
this --- Bone Stress:
http://www.exploratorium.edu/snacks/bone_stress.html
Deb
>Eric,
>
>You are observing the change in optical rotation of polarized light
>produced by clear materials under mechanical stress. This phenomenon is
>used to view stress concentrations in plastic models of structures that
>are put between crossed polarizers. It's called photoelasticity or
>photostress on the web. Yhe Exploratorium may still have an exhibit
>showing an arched structure, an also a femur model under variable
>stress. You can probably try this by wearing polarized glasses, and
>looking at (not just through) a flexible piece of clear plastic, with
>another
>polarizer lens behind the plastic, this lens rotated to look dark. When
>the plastic is bent, the characteristic stress contours should be visible
>in the plastic. The light from the sky is slightly
>polarized, and some of the windows have been deliberately manufactured to
>contain residual stress, so that they shatter into relatively dull
>'cubes' instead of jagged shards. There may also be stresses on the
>windows from just being mounted on the car. I hope this is what you are
>looking for; and that it doesn't contain any urban legends.
>
>Jeff.
>
>
>> > Subject: automobile
>window polarization splotches > From: "Eric Plett" <EPlett@serrahs.com>
>> Date: Wed, 21 Apr 2004 14:44:33 -0700
>>
>> Hello All.
>>
>> For the past few years I've wondered why you see round splotches
>>on windows while wearing polarized sunglasses. More expensive cars
>>have smaller, more compact sets of splotches. I've offered extra
>>credit to students who could find the answer - none succeeded.
>> I just tried to find something on Google with no success. Can
>>anyone explain this?
>>
>> Thanks in advance, Eric Plett.
>>
>
>
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-- Deborah Hunt Senior Information 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
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