General Q about fluids

[4563728]

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If something is sinking in, say, water will there be a point in which the object stops sinking and floats in the liquid becasue the weight of water above the object equals the weight of the object? Or will it continue to sink until it reaches the 'bottom' of the container because it is more dense than the liquid?

Also, is buoyancy force constant once an object is fully submerged?

 

[inasensegone]

Your question can be answered a few different ways... but basically, buoyancy force is given as follows:

Buoyancy force = Volume of fluid displaced * density of fluid displaced * gravity.

So, assuming that the object is more dense than water, the only way that the object will stop sinking is if something changes. An object that sinks in water is more dense than water. If the object were to suddenly increase in volume without an increase in mass and its density were to become equal to water (specific gravity of 1), then it could theoretically stop sinking. In actuality however, as an object sinks, it tends to become more dense because of compression. Consider the opposite, which may be what your question is referring to: If you take something like a balloon filled with air (obviously less dense than water), and swim it down toward the bottom of the ocean, the balloon would become more and more compressed as pressure increases. Eventually the air in the balloon could theoretically become dense enough that the density of the balloon is equal to water, and the balloon will no longer rise.

Based off of your first sentence, I think you may lack a fundamental understanding of buoyancy, density, pressure, etc. If the object is sinking in water, how would an increased weight of water above the object cause it to stop sinking?

 

[DrknoSDN]

If something is sinking in, say, water will there be a point in which the object stops sinking and floats in the liquid becasue the weight of water above the object equals the weight of the object?

Yes, but water is very close to incompressible. It would take an object that is truely incompressible and extreme depth to have something like that occur.
But if your asking strickly "theoretically", yes, as depth increases in a fluid that has a compressibility factor > 0. An in-compressible object would eventually stop sinking because the buoyant force would = mass of object.

Also inasensegone already answered what factors determine buoyancy. However charts online can show that if a few hundred (or thousand) atms of pressure is applied to water, it's density can go up by a percent or two. So an in-compressible object with density between 1.00 g/cm and 1.04 g/cm can sink deep enough it will eventually stop sinking in the worlds oceans.
http://www.engineering.uiowa.edu/~cfd/pdfs/tables/1-42B.pdf

Real World Application quote from wikipedia: http://en.wikipedia.org/wiki/Mariana_Trench
"At the bottom of the trench the water column above exerts a pressure of 1,086 bars (15,750 psi), over 1000 times the standard atmospheric pressure at sea level. At this pressure the density of water is increased by 4.96%, making 95 litres of water under the pressure of the Challenger Deep contain the same mass as 100 litres at the surface. The temperature at the bottom is 1 to 4 °C."

 

[inasensegone]

Yes, but water is very close to incompressible. It would take an object that is truely incompressible and extreme depth to have something like that occur.
But if your asking strickly "theoretically", yes, as depth increases in a fluid that has a compressibility factor > 0. An in-compressible object would eventually stop sinking because the buoyant force would = mass of object.

Also inasensegone already answered what factors determine buoyancy. However charts online can show that if a few hundred (or thousand) atms of pressure is applied to water, it's density can go up by a percent or two. So an in-compressible object with density between 1.00 g/cm and 1.04 g/cm can sink deep enough it will eventually stop sinking in the worlds oceans.
http://www.engineering.uiowa.edu/~cfd/pdfs/tables/1-42B.pdf

Real World Application quote from wikipedia: http://en.wikipedia.org/wiki/Mariana_Trench
"At the bottom of the trench the water column above exerts a pressure of 1,086 bars (15,750 psi), over 1000 times the standard atmospheric pressure at sea level. At this pressure the density of water is increased by 4.96%, making 95 litres of water under the pressure of the Challenger Deep contain the same mass as 100 litres at the surface. The temperature at the bottom is 1 to 4 °C."

Ahhhh... very cool perspective... although I don't think that this is what the OP was asking about. He asked about the weight of the water above the object being equal to the object. What you're referencing is that the weight of the water above some great depth, causes an increase in the density of water at that depth, and that this may lead to altered buoyancy.

 

[4563728]

These were great explanations, I understand it much better. Thank you!