Pressure on a submerged object

[MN-Andrew]

New member: Stem cell biologist by training, and many years since my last physics class.

Imagine I take a water balloon and fill it completely with water. I then submerge the balloon in a beaker of water and place the glass inside a sealed chamber. What forces are applied to the water balloon when I force air to the chamber (to X psi)?

Is the force on the water balloon the same if the water balloon is in a chamber completely filled with water and water is forced into the chamber (to X psi)?

 

[anorlunda]

You can answer your own question. Submerge an open jar in water. Does the pressure change if you then put the top on while it is submerged?

The key to your answer is the compressibility of the fluid outside compared to the compressibility of the fluid inside.

 

[MN-Andrew]

Sorry, I guess I should've gotten more to the point of this question, but I was a little pleased with myself for making the water balloon analogy.

The whole purpose of the question was to see if I could find a way to mimic intracranial pressure in a dish of cells. For background: When someone gets a head injury, there is a buildup of fluids within the skull, but the skull prevents the release of those fluids and doesn't expand, thereby increasing pressure on all the cells in the brain. A basic cell culture setup requires a gas-liquid interface to keep the cells happy and oxygenated (the cells will be submerged under only 1-2cm of media and placed in the incubator). So, in relation to my first questions above, if I compress the 20% O2, 5% CO2 gas mixture to a set psi inside of sealed incubator, how is that pressure translated to force applied to the cells submerged in media? In relation to my second question, how can the forces of this gas-liquid interface model be translated to the patient where all the force is due to more liquid in the system.

 

[sysprog]

Sorry, I guess I should've gotten more to the point of this question, but I was a little pleased with myself for making the water balloon analogy.

The whole purpose of the question was to see if I could find a way to mimic intracranial pressure in a dish of cells. For background: When someone gets a head injury, there is a buildup of fluids within the skull, but the skull prevents the release of those fluids and doesn't expand, thereby increasing pressure on all the cells in the brain. A basic cell culture setup requires a gas-liquid interface to keep the cells happy and oxygenated (the cells will be submerged under only 1-2cm of media and placed in the incubator). So, in relation to my first questions above, if I compress the 20% O2, 5% CO2 gas mixture to a set psi inside of sealed incubator, how is that pressure translated to force applied to the cells submerged in media? In relation to my second question, how can the forces of this gas-liquid interface model be translated to the patient where all the force is due to more liquid in the system.

Gases and liquids are both fluids, but gases are highly compressible and liquids are not.

Intracranial pressure is complex even absent the context of head injury. There are many localized effects, due to arterial pressure being greater than venous pressure, different sizes of blood vessels, systole and diastole, etc.. When you add injury, there are a number of complications, including, for example, changes in responses of intracranial vascular smooth muscle cells.

It seems to me that you would benefit from reading up on the ABCD gas laws and hydrostatics, and also from some exposure to what's involved in fluid dynamics.

Then decide, for your experimental purposes, what features of the interplay between gases, liquids, and pressures you most would like to mimic, and take it from there.

I find intriguing your idea of trying to reduce the difference between the in vitro and in vivo environments.

 

[MN-Andrew]

Thanks sysprog. The links are very helpful and are bringing back some familiar concepts from years ago. If you're at all interested in hearing more about this project or have a few thoughts on design/experimental variables, I would love to hear it. Feel free to message me.