Balloon within a balloon question

  • Thread starter mikdes
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I am curious, last night we had a discussion about the “what if”.
Maybe someone on this board can answer.
Here is the scenario. In a space ship you have 2 balloons.
One is fill with a liquid, connected to a a liquid tank with a tube and inserted into another, that is fill with air.
As you increase the pressure of liquid [through a tube that is connected to the liquid fill balloon] you increase the air pressure in the other balloon.
You keep both of them at even pressure.
It would be assume the liquid fill balloon would keep its original dimension and the air balloon would expend.
At the moment the air balloon burst, and without the constrain of gravity, the liquid fill balloon would immediately expand, and in this scenario, would burst open [cheap balloon, no elasticity]

Now here is my question, do you think the liquid would?
a- immediately reach its maximum speed then slow down
b- increase its speed until it reach a maximum, then slow down

Believe it or not, me and my girls are having this type of conversation at the dinner table.

Hopefully someone out there knows the answer and will settle this argument.
Thanks in advance
 

Answers and Replies

  • #2
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Most importantly:
Believe it or not, me and my girls are having this type of conversation at the dinner table.
Kudos to such wonderful dinner conversation, the future of humanity thanks you! :)

Forgive me if I misunderstood something:
As you increase the pressure of liquid [through a tube that is connected to the liquid fill balloon] you increase the air pressure in the other balloon.
You keep both of them at even pressure.
It would be assume the liquid fill balloon would keep its original dimension and the air balloon would expend.
At any given time, for the system to be stable, the pressures must all balance (i.e. a stationary object must have no net force on it). Thus the outward fluid pressure must be balanced by a combination of the inner-balloon elasticity, and the air pressure in the second balloon. Then the air pressure in the second balloon must also be balanced by the elasticity of the second balloon and the ambient air pressure. Because the liquid exerts little pressure, I think your assumption that it changes negligibly in volume. Cool.

At the moment the air balloon burst, and without the constrain of gravity, the liquid fill balloon would immediately expand, and in this scenario, would burst open [cheap balloon, no elasticity]
This is a little weird, but I think its fine....

Now here is my question, do you think the liquid would?
a- immediately reach its maximum speed then slow down
b- increase its speed until it reach a maximum, then slow down
Its impossible to answer this question exactly with the given assumptions, simplifications and lack of a specific type of fluid. In general however:
As soon as there is no force acting on the liquid it will stop speeding up (it also won't slow down or the same reason). If it was something water, then it would adhere to itself, perhaps keeping it together---and in that sense "slowing it down," and would begin oscillating. Something like light oil, or liquid methane (etc etc etc) would fragment and not slow down at all (essentially splashing outward---but this would depend on their being an atmosphere in the spaceship). So it really depends on the particulars of the situation you're envisioning.

I feel like this is an incredibly unsatisfying response, so please feel free to clarify your situation or explain what your imagining and perhaps we can be more specific.
 
  • #3
The "spring constant" of a liquid is very high. When the exterior balloon popped, the pressure suddenly changes on the liquid balloon. The liquid would expand (a tiny bit) - and that very little expansion would allow it to drop in pressure to match the environment. So for a small amount of time and small increase in liquid volume, the liquid would accelerate outwards (i.e. "expand").

After that, momentum could keep it expanding if it broke up into droplets (since the total liquid volume wouldn't change). Those droplets would very gradually slow down due to air resistance. If the liquid's surface tension was strong enough, the momentum might be converted to heat as the liquid blob vibrated like jello and finally settled down to be one giant sphere.

Of course, the ripping of the cheap inner balloon would do things, but I didn't think you were interested in that. It just "disappears" in this thought experiment.
 
  • #4
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thank for the answers.
this conversation started about dark energy and we were trying to explain, in our own way how can you increase momentum in the expansion of the matter [i used liquid in my example] as an alternative way to explain an outward pulling force .
in my example i should have mention that outside the second balloon was a total void.
the air in the second balloon was suppose to represent our physical universe.
sorry for the lack of details . i know this is far of the beaten path and i didn't want to have a long draw conversation about the merit of this "hair brain" theory of ours.
just a dad and 2 girls shooting the breeze.
thank you CBargainer for your answer.
 
  • #5
I had to laugh, my reply was so poorly matched to your real interest! Still, it was fun to answer as if the balloons were floating in the ISS. I'm totally unqualified to talk "dark energy", but I'm ok with water balloons. I like the family discussion topic, though!
 

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