Many fluid problems do not involve motion rather concerned with the pressure distribution in a static fluid. When the fluid velocity is zero, known as hydrostatic condition, the pressure variation is due to weight of the fluid. The important areas of fluid statics include;
- • Pressure distribution in atmospheres and oceans
• Design of manometer pressure instruments
• Forces on submerged flat and curved surfaces
• Buoyancy on a submerged body
• Behavior of floating bodies
Hydrostatic pressure for fluids
- • The term ‘pressure' is used to indicate the normal force per unit area at a point acting on a given plane within the fluid mass of interest. It is governed by Pascal's law which states that the pressure at a point in a fluid at rest or in motion is independent of direction as long as there is no shearing stress present.
• The net pressure force acting an fluid element per unit volume 
is given by,
 |
(1.2.1) |
It is not the pressure but the pressure gradient that causes the net force.
• In engineering applications, the pressure is measured either as absolute numbers (called absolute pressure) or relative to atmospheric value (gauge/vacuum pressure). If the atmospheric pressure is given as pa, then referring to Fig. 1.2.1,
• Pressure at ‘A' can be measured as gauge pressure 
or absolute pressure (p1) i.e.
 |
(1.2.2) |
• Pressure at ‘B' can be measured as vacuum pressure 
or absolute pressure (p2) i.e.
 |
(1.2.3) |