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    Re: Sperm whale buoyancy.
    From: Alexandre Eremenko
    Date: 2007 Mar 26, 18:25 -0400

    
    The skull (or anything else in our body) can not
    resist a pressure of 200
    atmospheres, or even of 2 atmospheres.
    And it does not have to.
    There is no air inside the skull (fortunately:-)
    And thus from the point of view of physics it
    is filled with a liquid (water). Water is incompressible.
    Same applies to all other parts of our bodies,
    (they are filled with liquid not with air), except
    the lungs.
    That's why we (and the whales) can dive.
    The limit of depth of free diving
    is mostly determined by how much
    the lungs can be compressed.
    That is what is the ratio of volumes between our
    "empty lungs" and full lungs.
    
    The world record for humans is some 180 meters
    (found in Wikipedia, 180 meters is amazing indeed!)
    The same Wikipedia says that a sperm whale can dive
    2 miles which is really hard to believe.
    It is not clear from the Wikipedia article how well
    this has been verified. They say "It is believed...".,
    The main evidence as I understand is some traces of
    sperm whale teeth on damaged transoceanic cables.
    
    Alex.
    
    On Mon, 26 Mar 2007, Fred Hebard wrote:
    
    >
    >
    > I was just thinking that the skull would resist the pressure more
    > than the lungs, so there would be a pressure differential between the
    > _interior_ of the skull and the lungs; but I'm no physicist nor
    > physiologist!
    >
    > On Mar 25, 2007, at 7:23 PM, George Huxtable wrote:
    >
    > >
    > > In reply to Fred Hebard's question, copied below, my answer is "No,
    > > I doubt it". The point being that whatever the sea pressure is,
    > > that is being applied to the lung-area of a sperm whale to collapse
    > > it, that same sea-pressure, and a bit more, is being applied to
    > > the head area, because it's a few feet lower down in the sea,
    > > because of the creature's head-down orientation as it makes its
    > > vertical dive. And surely, those pressures must transmit themselves
    > > to the whale's interior, because it's constructed of such
    > > flexible stuff. So I don't quite see how the remaining bubble of
    > > air remains at that lower level, unless it's held there by some
    > > muscular power creating a bit of extra pressure at the level of the
    > > lungs.
    > >
    > > But there's a lot of speculation in that, and much ignorance, on my
    > > part. I'm simply doing my best to apply physical principles to a
    > > whale/water system. We need access to an expert on whale
    > > physiology. I wonder where you find a helpful cetologist?
    > >
    > > We are discussing fine points here, and unlike the sperm whale, I
    > > am well out of my depth.
    > >
    > > George.
    > >
    > > ================
    > > |
    > > | Wouldn't the pressure difference be provided by the sea in the form
    > > | of the collapsed lungs?
    > > |
    > > |
    > > | On Mar 25, 2007, at 1:24 PM, George Huxtable wrote:
    > > |
    > > | > That mechanism for avoiding the "bends" seems plausible, but
    > > there's a
    > > | > question occurs to me that isn't answered. As explained by Watson,
    > > | > those air receptacles, being in the head, are many feet below
    > > the lung
    > > | > area, when the whale is diving, almost vertically, with its
    > > head down.
    > > | > So how does the whale ensure that the remaining bubble of air,
    > > | > shrinking as it compresses, doesn't float upwards into the
    > > lungs, but
    > > | > instead stays down at the head-end? That must be achieved by
    > > some sort
    > > | > of muscular control of the chest cavity to provide the necessary
    > > | > several-pounds-per-square-inch of pressure difference.
    > >
    > > contact George Huxtable at george---.u-net.com
    > > or at +44 1865 820222 (from UK, 01865 820222)
    > > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > >
    > >
    > > >
    >
    >
    >
    > >
    
    
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