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Hi Cobie,

I have a habit of exposing my ignorance but I think you can achieve some 
of what your after with a simple set up.   Just to try, place a small 
mirror (square foot mirror tile would work okay) outside and aim it so 
it shines a little piece of sunlight into a somewhat dark room (sunlight 
is so bright that the room doesn't really have to be very dark.)  In the 
beam of sunlight place a lit match or other heat source.  In the shadow 
on the wall you should very clearly see convection currents swirling off 
the match. 

I know the match trick works fine - it gives off enough heat to overcome 
other convection currents in this very uncontrolled set up.  In a more 
controlled environment even the heat off your hand can work. I'm not 
sure about the organ pipe, but in a more tightly controlled set up is 
should work fine as well.

I think the sunlight basically takes care of most of your optics.  That 
light all ready arrives collimated, more or less.  The set up you 
describe sounds like it provides a much more controlled, lab-like, 
environment, which frees you from sunlight and makes the whole thing 
portable. I sure do like the simplicity of the sun, though.

Try the little demo with the sunlight and then look up Schlieren Optics 
on the web.

I hope this helps. If you discover that I've got it all wrong, please 
let me know.

All the best to you folks over there.


Joe R
www.TheExhibitGuys.com






Cobie Howard wrote:

>ISEN-ASTC-L is a service of the Association of Science-Technology Centers
>Incorporated, a worldwide network of science museums and related institutions.
>*****************************************************************************
>
>Hi,
>We are trying to build an exhibit that allows visitors to see a shadow of
>the airstream that flickers in and out of the mouth of an organ pipe.  I
>have heard that this is possible using some arrangement of a strobe light,
>polarizing filters and collimating lenses.  Does anybody have any tips or
>resources to help us do that?
>Thanks,
>Cobie Howard
>Exhibit Developer
>Explora Science Center and Children's Museum of Albuquerque
>505-224-8306
>
>
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