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Water incompressible

  1. Jun 19, 2014 #1
    A book about liquid mechanics, says that water is considered incompressible , because the amount by which it compresses is too tiny to bother with.

    My question is , what would happen with a metal ball or sphere filled with water and put into extreme conditions , like in the very center of sun or earth.At the temperatures and pressures present all metals normally melt and disintegrate , but the water inside would increase its temperature and water vapour would increase the pressure so the boiling point would also increase , would this happen until the water pressure inside the sphere equal the pressure from outside the sphere ?
  2. jcsd
  3. Jun 19, 2014 #2
    Ice will form.


    However, if you put some water into the center of a star, then the oxygen and hydrogen atoms would undergo fusion.
    Last edited: Jun 19, 2014
  4. Jun 19, 2014 #3
    thank you for the answer, I was interested in the material properties of such a sphere ,
    so under such pressure and temperature the water inside the sphere would become ice , what would happen to the metal sphere when this happens ? normally we understand ice is when the temperature is low but here it would be likle hot ice?

    I guess the question then becomes does steel melts in such configuration and pressure , ice from one side , plasma from the other.Kinda mind boggling.
  5. Jun 19, 2014 #4
    It is not normal ice. Normal ice at that temperature would melt. But the increased pressure form "special ice". See in the phase diagram where there are lines between blue areas? These are the boundaries of different types of ice (different crystal structures). Ice at the temperature and pressure you are looking at would be more dense than liquid water, which is something you wouldn't expect otherwise, no?

    I don't know why you think the metal part of the ball would melt. It would remain solid due to the pressure (perhaps transitioning to a different crystal structure). Remember, the iron in the center of the earth is solid due to the extreme pressure. That is a sweeping generality I've drawn, and won't claim it's true for all metals (because I don't know for sure), but it certainly goes for iron and most likely for many others.

    What happens to the metal at the center of a star I don't know. Maybe it will start fusing into heavier metals, maybe it will just sit there. I leave that to someone smarter than I am.
  6. Jun 19, 2014 #5

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  7. Jun 19, 2014 #6


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    At the center of the Sun, the temperature is ~15 million K. The average thermal energy is is then ~kT=1.3keV. This is high enough of a thermal energy that no atoms will remain bound (binding energy of Hydrogen is only ~13.6eV, this thermal energy is 100 times higher). No atomic states are possible, and so you just have a plasma.

    The molecules in water would all be destroyed and you'd just have hydrogen and oxygen nuclei and electrons freely flying around.
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