2.0 FLUID PRESSURE
2.1 Pressure and pressure variation in a fluid at rest.
The pressure indicates the normal force per unit area at a given point acting on a given plane. Since there is no shearing stresses present in a fluid at rest - the pressure in a fluid is independent of direction. For fluids - liquids or gases - at rest the pressure gradient in the vertical direction depends only on the specific weight of the fluid. Direction of the pressure-induced forces in a fluid at rest because fluids deform continuously when exposed to any shear stress at all, the only force that can be applied to a surface in a fluid at rest must be normal to that surface.
Thus, as a (real or imaginary) surface is moved in any direction in a fluid, the force on it shifts to always remain perpendicular to every part of the surface. Fluid at rest is no shear stresses and only normal forces due to pressure
2.1.1 Concept of pressure and pressure head
Intensity is the amount of atmospheric pressure and the weight of the fluid at a unit area at one point or surface. Usually the pressure intensity referred to as pressure only.
The pressure at depth h is γh
Pressure, P = γh kN/m2
= ρgh ………………………………………………..( 3.1) where h is measured in vertical
Pressure in water is proportional to the depth in the fluid may be indicated by a triangle as in diagram above. If there is a small body in the fluid does not move, pressure must be the same intensity in all directions to maintain the value of equilibrium. Lines of action of pressure forces must perpendicular to any surface of the body. Any two points at the top the same horizontal plane must have the same pressure.
A working diver 18m below sea level. Calculate the pressure suffered due to the water column. (specific weight of water = 10,000 N/m3)
P = ωh kN/m2
= 10,000 X 18