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 PRESSURE AND DEPTH


When a liquid (such as water, oil etc) is contained in a vessel, it exerts force at all points on the sides and bottom of the container. This force per unit area is called pressure. If  F is the force acting on an area a, then intensity of pressure is :

P= F/A


The direction of this pressure is always at right angle to the surface, with which the fluid at rest, comes into contact.

The intensity of pressure at any point is the force exerted on an unit area at that point and is measured in Newtons per square metre, N/m2 (Pascals). An alternative metric unit is bar, which is in N/m2. 

  
 FLUID STATIC                                                                        

    
 Let a cylinder be made to stand in the liquid as shown in the figure. The weight of liquid contained in the cylinder is ωhA where ;

ω = Specific weight of the liquid ( where is ω water  = 1000 kg/m3 x 9.81 m/s2) h = Height of liquid in the cylinder A = Area of the cylinder base

The pressure, at the bottom of the cylinder, will be due to the weight of the liquid contained in the cylinder. Let this pressure be p.

Then,
p= weight of liquid in the cylinder/area of the cylinder base

This equation shows that the intensity of pressure at any point, in a liquid, is proportional to its depth as measured from the surface (as ω is constant for the given liquid).