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

[Brian Whatcott <betwys1@sbcglobal.net>]

Quist, Oren wrote:
> 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).
I'll bite...
The buoyant balloon in contact with the roof is rocked by a motion 
travelling at c for steel; say 5000 ft/sec. In an SUV, the contact point 
might be 3 ft from the windshield and 3 ft from the tailgate.
We could take this as a 0.6 millisecond time delay to sense the roof 
acceleration, and a 3 millisecond transmission time for the rarefaction 
and compression waves to reach the balloon, that one could imagine if 
all air access into the vehicle were closed off.
  The most effective step acceleration would originate in a stamped 
foot brake application.
This might possibly reach 1 g horizontally but probably less, in a ramp 
over 120 plus milliseconds.
Vehicles often  nose dive under braking but I will overlook this.
For an initial 2.4 milliseconds a linear horizontal acceleration ramp 
from 0 to 1g/ 120 milliseconds
might provide traction for a (slight?)  angular balloon rotation, for 
these parameters....

Brian W