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I have a favorite explaination that I came up with for the Bernoulli effect.
Simple enough to get across to kids yet completely factual:  Ready?

Air, so busy going in this direction can't push much in that direction (90
degrees to the first direction).

With the Einstein quote in mind-"Things should be as simple as possible-but
no simpler!"  you might have to add that still air is actually pushing in
all directions; that it has pressure, and that it can often push more than .
(How to explain pressure?  Air at sea level is under about 14.1 pounds per
square inch.  How to explain that?  Picture a one inch square on your hand.
Now if you visuallize that one inch square as the column of air going from
you hand straight up all the way out to space, that column of air weighs
14.1 pounds.  Because air is a fluid it pushes in all directions, not just
down, but it is the weight of the air above that gives it the pressure.   Go
up the mile higher to Denver and the air pressure is considerably less- less
5,280 feet x1"x1" of air than you have on top of you at sea level
So the complete explaination for why the ball stays in the fast moving air
column is that air busy moving up can't push as much sideways as the still
air around it.  It is the pressure of the still air that holds the ball in
place.

My favorite bernoulli device is the upside down funnel with air coming out
pointing straight down.  Put a ball inside the funnel and it stays up,
defying both gravity and the air pushing down.  But with the explaination
above, it is explainable.  The air has to escape between the sides of the
ball and the inside of the funnel.  That air, so busy going past the ball,
pushes less directly on the ball (yes, it exerts less pressure)  than the
still air underneath the ball.  The still air holds the ball up.  If you do
this device make a clear funnel so you can see the ball and the nothing else
holding the ball up.  (heat and bend 3/8"plexi is how I did  a pretty
indestructable version)
We did at the Franklin Institute a whole series of devices on one Bernoulli
table in our 1984 version of an Aviation exhibit.  It worked really well
having the multiple examples all next to each other:  The upside down funnel
(with compressed (Pressured! I never made made that connection clearly
before! ) air) and four other devices all worked by manipulating vacuum
cleaner hoses that were blowing out instead of in.  They were: a vertical
plexi tube with a whiffle ball (without holes) inside the tube.  Blow the
air across the top and the ball rises in the tube.  A cross section of an
airplane wing with little balls inside little tubes all vertical, spaced
evenly apart visible inside the wing.  Blow the air over the wing and just
like the big tube and ball most of the little balls rise. We were looking
for visitors to connect between the two and I think many did.   We also had
a clear 8inch square house with a thin plastic slanted roof taped to the
rest of the house with scotch tape on one edge.  Blow the air over the roof
and -voila!  the roof lifts off.  Put a weather channel video there next to
it and you've got visitors inspired to act mighty powerfully on the model,
while thinking through Bernoulli lifts roofs!   We also had the hanging on
3' long pivoting rods bowling balls that would come together when you blew
air between them as was mentioned before.   Having all of these together
helped get the idea across.

Bill Booth was the project leader for this Aviation exhibit.  I think it was
his idea to have tham all together.
 There was one other great device in the exhibit that I haven't seen
elsewhere that really should be done again.  Titled "Air can do work" or
"Air Does Work"  it was two 4" diameter graphite pistons in precision glass
tubing, each glass tube about a foot long.  They were connected to each
other to form a U shape on the table with bent 4" glass tubing forming the
curved parts, so you could see that the only connection between them was the
air inside the tubing.   Each piston had a handle sticking out so you could
push and pull them.  There was a vacuum/pressure guage connected to the
airspace between the pistons.   Push one piston in and the other would push
out with almost the same amount of force.  Two visitors would often "fight"
each other, proving to them in their play that Air indeed can and does work.
Push both in at the same time and you got a bit of pressure reading on the
guage.  It was hard to get much pressure, even when pushing hard, again a
personalized demo of air having force/resistance, and, without too much
imagination necessary,  the ability to keep airplanes aloft.
You could also pull both and get a bit of a vacuum.
A classic device.
It only lasted five years until someone broke one of the glass tubes (they
had a wall thickness of 3/8" to 1/2")  and for some reason it was deemed too
costly or hard or something to get replacement glass.  A mistake not to fix
it in my book.  It's easy enough to design it so a plexi cover would keep
the most determined urchin from having the ability to break the glass.   The
graphite pistons were as good when the device died as they were when it was
born, so without the breakage it's a reliable device.

So much for simple Bernoulli explainations.

A still constantly learning Clifford Wagner

It
-----Original Message-----
From: Andrea Stark [mailto:[log in to unmask]]
Sent: Monday, August 30, 2004 3:02 PM
To: [log in to unmask]
Subject: Bernouilli exhibits


ISEN-ASTC-L is a service of the Association of Science-Technology
Centers Incorporated, a worldwide network of science museums and related
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We'd like to make changes to our Bernouilli exhibit, which now consists
essentially of several small blowers that can be moved around to keep
ping pong balls in the air and/or "make a basket" with them.  Does
anyone have examples of more interesting exhibits that demonstrate
Bernouilli's principle or otherwise deal with air flow and could capture
the attention of older visitors, yet be operable by younger visitors to
our children's museum?

Andrea Stark
Executive Director
Maine Discovery Museum
74 Main St., Bangor, ME 04401
207-262-7200; FAX: 207-947-6281

www.mainediscoverymuseum.org

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