2 Water at Rest and in Motion
2.1 Introduction
This chapter has been divided into two main parts: hydrostatics and hydrodynamics. Hydrostatics is the study of water (hydro) at rest (static), and
includes the investigation of distribution of pressure within the water body and
buoyancy forces. Although both pressure and buoyancy are acting no matter
whether water is at rest or in motion, it is useful to explain them first for the
simpler case of water at rest. Hydrodynamics is the study of water in motion. As there are many types of water motion in the ocean, it is not possible to
discuss them all in one chapter. However) some properties of the sea water motion are common and can be discussed independently of specific types of water
motion. This is particularly true for such properties as steady and unsteady
flow, rotational and irrotational motion, and laminar and turbulent flow. The
basis of all these types of sea water motion is covered in this chapter. The
following chapters are devoted to particular types of motions, such as surface
waves, tides, currents and internal waves.
The significance of some physical properties of water and its motion reveal
themselves at specific conditions of motion. However, prior to starting our
discussion on the physics of water at rest and in motion, we must first establish
a coordinate system through which objects can be located in space and water
motion can be described.
2.1.1 Coordinates System
Throughout this book the Cartesian system of coordinates will be used (Fig.
2.1a). This system was invented by a French philosopher and mathematician
Rene Descartes, as a result of a dream on the night of 10 November 1619
(Barber, 1969). For this coordinate system, the axes Ox, Oy, Oz are mutually
perpendicular, and the x and y axes lie in a horizontal plane, leaving the z
axis to point vertically. However, in some cases (for example, when discussing
depths in the ocean) it will be convenient to point the z axis downward.
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999
2.1 Introduction
This chapter has been divided into two main parts: hydrostatics and hydrodynamics. Hydrostatics is the study of water (hydro) at rest (static), and
includes the investigation of distribution of pressure within the water body and
buoyancy forces. Although both pressure and buoyancy are acting no matter
whether water is at rest or in motion, it is useful to explain them first for the
simpler case of water at rest. Hydrodynamics is the study of water in motion. As there are many types of water motion in the ocean, it is not possible to
discuss them all in one chapter. However) some properties of the sea water motion are common and can be discussed independently of specific types of water
motion. This is particularly true for such properties as steady and unsteady
flow, rotational and irrotational motion, and laminar and turbulent flow. The
basis of all these types of sea water motion is covered in this chapter. The
following chapters are devoted to particular types of motions, such as surface
waves, tides, currents and internal waves.
The significance of some physical properties of water and its motion reveal
themselves at specific conditions of motion. However, prior to starting our
discussion on the physics of water at rest and in motion, we must first establish
a coordinate system through which objects can be located in space and water
motion can be described.
2.1.1 Coordinates System
Throughout this book the Cartesian system of coordinates will be used (Fig.
2.1a). This system was invented by a French philosopher and mathematician
Rene Descartes, as a result of a dream on the night of 10 November 1619
(Barber, 1969). For this coordinate system, the axes Ox, Oy, Oz are mutually
perpendicular, and the x and y axes lie in a horizontal plane, leaving the z
axis to point vertically. However, in some cases (for example, when discussing
depths in the ocean) it will be convenient to point the z axis downward.
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999