Fluid Compressibility and Dinosaur Social Warmth

["Ray Stanford" <dinotracker@earthlink.net>]

David Marjanovik said,

"Ask any professor of physics -- fluids ARE compressible, just less so than
gases and spongy solids."

    Yes, indeed.  Haven't we all heard of sonar?  -- and, for that matter,
those well-documented recordings of the 'songs' of whales?  Those whales
were not 'singing' in the open air, whales have ears to hear under water,
and whale 'songs' have been recorded using aquatic microphones.  Water is
being usefully compressed (modulated compression) for such purposes.

    Yet, Al Fraser reported:

"Yes, water (the relevant fluid) is compressible.  The volume coefficient of
compressibility per atmosphere of pressure is approximately 0.00005.
Therefore, at say, 3000 feet deep (about 100 atmospheres pressure), water
will compress fractionally by 0.005.  That means that the linear dimensions
of water (or a sack of water) will change by 0.17% as the water goes from
the surface to 3000 feet deep.  That is very little compression, and hence
water is described, as an approximation, as incompressible.  Much fluid
mechanics of water is done well with the approximation that the
compressibility coefficient is zero."

    O.K., that information is appreciated, but whales (and submarines) take
advantage of water's compressibility quite effectively at depths less than
3,000 feet, and I would be greatly surprised to learn that prehistoric
marine reptiles frequented the 3,000 foot depth.  So is water's
near-incompressibility at 3,000 feet really meaningful in the context of our
discussion?  Or, do we debate dinosaurs' ability to breathe at ten miles
altitude? :-)

    Ray Stanford