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Re: [Phys-l] balloon floating in air in car



I'm agreed, though, with Oren, that the _minimum_ time (barring things like shock waves) to communicate to the balloon that anything weird is going on is roughly:
L/(2c),
where L is the length of the car's interior, the factor of 1/2 comes from the possibility of the balloon being in the front half of the car, and the relaxation wave from the car's front windshield influencing it, and c the usual speed of sound in air.

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________________________________
From: "Quist, Oren" <Oren.Quist@SDSTATE.EDU>
To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
Sent: Saturday, April 25, 2009 9:07:39 AM
Subject: Re: [Phys-l] balloon floating in air in car

A little disappointing that no one seems willing to pick up on this as there is some good physics involved.

The accelerating car would set up a pressure wave in the air. The time to affect the balloon would be proporsional to the car's interior dimension divided by the speed of the pressure wave (speed of sound).

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker [jsd@av8n.com]
Sent: Friday, April 24, 2009 1:55 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] balloon floating in air in car

On 04/22/2009 02:28 PM, Quist, Oren wrote:
I would venture that the tau depends upon the speed of sound in the
air in the car.

Indeed it does. That is a good place to start.

As the next step, to convert the speed of sound (c) to a time (tau),
we need a distance. A physically-relevant distance. Options
include:
-- Multiply c by the mean-free-path of the air molecules?
-- Multiply c by the diameter of the balloon?
-- Multiply c by the size of the car interior?
-- Bring in some other physics?


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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l