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Re: [Phys-l] Space Balloon



Like Bob, I have used the "balloon-in-an-accelerating-car" example for
many years. The pressure differential that produces buoyancy depends on
the total weight of the air increasing as one goes "downward". The
direction "downward" can be easily found by dropping a set of keys and
watching which way it falls. "Upward" is in the other direction.

If you are driving a car and suddenly apply the brakes while
simultaneously releasing a set of key from your hand, no one questions
that the keys fall toward the front floorboards of the car. That defines
"downward". That is the direction of increasing weight of the air in the
car. The balloon will float in the opposite direction, toward the
ceiling and tilted to the rear of the car.

The rotating jars demonstration with fishing floats or candle flames
gives totally unambiguous verification of this effect. It's very
counterintuitive for the students and really gets them thinking about
what centripetal force really means.

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of Bob Sciamanda
Sent: Wednesday, February 21, 2007 8:49 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Space Balloon

For about 40 years I have done this demo with both hooded candle
flames
and
tethered bobs in water. On a rotating platform, both the flames and
the
bobs move inward toward the axis of rotation. This is not a slight
effect.
It is obvious to the casual observer, even at a quite slow rpm of
rotation.
Linear acceleration of the platform produces confirming results.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.winbeam.com/~trebor/
trebor@winbeam.com
----- Original Message -----
From: "Brian Whatcott" <betwys1@sbcglobal.net>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Wednesday, February 21, 2007 8:31 AM
Subject: Re: [Phys-l] Space Balloon


. . .
This note is not intended to be cynical, but I ponder, in view of
the scattered views on blobs and balloons in spacecraft, just
what the considered response of the readership would be?

For myself: I can see that if the draft-proofing were all but
perfect,
the flame would still move in a particular way when the rotor
spins.



Brian Whatcott Altus OK Eureka!


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