Sink or float, high density low pressure VS low density high pressure

  • #1
Albertgauss
Gold Member
236
20
Normally, an object with a high density will sink in a fluid with low density. What if, as depth increases, as in the case of the ocean, the pressure really gets cranked up -> Is it possible for a low-density, high-pressure fluid to float a high-density object, that, under normal conditions would sink in the low-density fluid?

The ocean is a perfect example. Though its density doesn't change much with depth, its pressure gets huge by the time you get to the bottom of the seafloor. At the the surface of the ocean, anything with more density than seawater sinks, but could such an increase in pressure cause a normally sinking object to float in deep ocean depths before it hits the sea floor? Can high pressure, alone, cause things to float? Or will, density always rule, no matter the pressure, in determining whether an object sinks or floats in any medium?
 

Answers and Replies

  • #2
Drakkith
Staff Emeritus
Science Advisor
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The pressure doesn't matter. It's whether or not the density of the liquid increases to the point that it surpasses the object.
 
  • #3
Nugatory
Mentor
13,244
6,127
Normally, an object with a high density will sink in a fluid with low density. What if, as depth increases, as in the case of the ocean, the pressure really gets cranked up -> Is it possible for a low-density, high-pressure fluid to float a high-density object, that, under normal conditions would sink in the low-density fluid?
If anything, it's the other way around. Liquids don't generally compress, so the density of the fluid doesn't increase much with increasing depth and pressure, hence no increase in buoyancy with depth. However, the increase in pressure can compress the object, increasing its density and therefore making it more likely to sink.

For example: Most people, if their lungs are full of air, will float to the surface from a depth of three meters under water. At a depth of 100 meters, the higher pressure compresses the chest cavity and the lungs enough that the overall density becomes greater than that of water, and the human body sinks even with full lungs.
 
  • #4
22
1
Density is the only important factor, sorry, it is definitely not possible to have dense objects float in less dense ones.
 
  • #5
Albertgauss
Gold Member
236
20
I got it everyone. Thanks for your help. I think I kind of knew, but one can always hope for surprises.
 

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