I.

Introduction

Fluid Mechanics, physical science dealing with the action of fluids at rest or in motion, and with applications and devices in engineering using fluids. Fluid mechanics is basic to such diverse fields as aeronautics (see Airplane; Aviation), chemical, civil, and mechanical engineering (see Engineering), meteorology, naval architecture (see Ships and Shipbuilding), and oceanography (see Ocean and Oceanography).

Fluid mechanics can be subdivided into two major areas, fluid statics, which deals with fluids at rest, and fluid dynamics, concerned with fluids in motion. The term hydrodynamics is applied to the flow of liquids or to low-velocity gas flows where the gas can be considered as being essentially incompressible. Aerodynamics is concerned with the theory of flight, and compressible fluid flow or gas dynamics with the behavior of gases under flow conditions, where velocity and pressure changes are sufficiently large to require inclusion of the compressibility effects.

Applications of fluid mechanics involve all kinds of flow machinery, including jet propulsion, hydraulics, turbine, compressors, and pumps (see Compressed Air; Pump). Hydraulics mainly concerns machines and structures such as hydraulic turbines, dams, and hydraulic pressures, using water or other liquids.