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The Collaborative International Dictionary of English v.0.48 (gcide)

Hydrodynamics \Hy`dro*dy*nam"ics\, n. [Hydro-, 1 dynamics: cf.
F. hydrodynamique.]
That branch of the science of mechanics which relates to
fluids, or, as usually limited, which treats of the laws of
motion and action of nonelastic fluids, whether as
investigated mathematically, or by observation and
experiment; the principles of dynamics, as applied to water
and other fluids.
[1913 Webster]

Note: The word is sometimes used as a general term, including
both hydrostatics and hydraulics, together with
pneumatics and acoustics. See {Hydraulics}.
[1913 Webster]


Mechanics \Me*chan"ics\, n. [Cf. F. m['e]canique.]
That science, or branch of applied mathematics, which treats
of the action of forces on bodies.
[1913 Webster]

Note: That part of mechanics which considers the action of
forces in producing rest or equilibrium is called
{statics}; that which relates to such action in
producing motion is called {dynamics}. The term
mechanics includes the action of forces on all bodies,
whether solid, liquid, or gaseous. It is sometimes,
however, and formerly was often, used distinctively of
solid bodies only: The mechanics of liquid bodies is
called also {hydrostatics}, or {hydrodynamics},
according as the laws of rest or of motion are
considered. The mechanics of gaseous bodies is called
also {pneumatics}. The mechanics of fluids in motion,
with special reference to the methods of obtaining from
them useful results, constitutes {hydraulics}.
[1913 Webster]

{Animal mechanics} (Physiol.), that portion of physiology
which has for its object the investigation of the laws of
equilibrium and motion in the animal body. The most
important mechanical principle is that of the lever, the
bones forming the arms of the levers, the contractile
muscles the power, the joints the fulcra or points of
support, while the weight of the body or of the individual
limbs constitutes the weight or resistance.

{Applied mechanics}, the principles of abstract mechanics
applied to human art; also, the practical application of
the laws of matter and motion to the construction of
machines and structures of all kinds.

{orbital mechanics}, the principles governing the motion of
bodies in orbit around other bodies under gravitational
influence, such as artificial Earth satellites.
[1913 Webster PJC]