Pressure Due to a Fluid Column

Pressure Due to a Fluid Column 

Pressure can be defined as the perpendicular weight on the surface of an object divided per unit area over which the force is distributed. Pressure is denoted with the symbol  P. In the case of pressure due to a fluid column; as the depth of the fluid increases, so does the pressure of the fluid.

Fluid pressure can be defined as the pressure in a fluid that increases with the fluid’s depth and weight. The following equation can be used to determine the pressure of a fluid column:

Pfluid  =P + ρgh

Where,

P denotes the pressure at the point of reference

Pfluid denotes the pressure at a specific point in a fluid

ρ denotes the density of the fluid

g denotes the acceleration due to gravity (taking into consideration for earth g= 9.8 m/s2)

and h denotes the height from the point of reference.

Fluid Pressure

Fluid pressure can be defined as the force per unit area on an object in the fluid or on the surface of a closed container. Fluid pressure is directly affected by the factors of external pressure on the container of the fluid, gravity and acceleration. 

Since it is apparent that fluid matters do not have an absolute shape or form, the pressure due to a fluid column is generated mainly on the basis of shifting of velocity or due to heightened hydraulic mechanisms of a fluid.

Fluid pressure due to gravity and acceleration

The pressure on a fluid column is the greatest at the bottom of the container that the fluid is stored in. The volume of fluid exerts pressure at the bottom of everything underneath it, and this pressure always falls perpendicular at any specific point of the fluid.

Let us first take a look at the definition of pressure and its derivation:

Pressure 

Pressure can be defined as the perpendicular force exerted on an object per unit area over which the force is distributed on an object. Pressure is measured in Pascal (Pa) units and is expressed by the symbols  P.

Pressure on the surface of a given object is calculated as:

P = F/A

Where, 

P denotes pressure

F denotes force 

and, A denotes area of the given object

Pressure due to gravity

The weight of an object always exerts a downwards force due to gravity. Also, the pressure exerted by any given object is directly dependent on the object’s surface area, which is in touch with the ground or the surface the object is placed on.

For instance, the pressure applied by the weight of a pencil box placed on a table would directly fall on the surface of the pencil box, which is in direct touch with the surface of the table. 

In case the pressure is directly related to the weight of then it can be derived through the following equation:

P = W/A

Where, 

P stands for pressure

W stands for the weight of the object

and, A stands for area

Liquid pressure

Liquid pressure is always directly related to the depth of the liquid, i.e., as the depth of the liquid increases, so does the pressure of the liquid. This is mainly due to the fact that the liquid at the lower surface levels has to bear the pressure of the liquid at the higher levels.

Hence, as the depth of the liquid increases, so does the pressure. This can be better explained with the example of the ocean, the deeper depths of the ocean has a greater amount of pressure than the surface of the ocean, and hence, the ocean floor has the maximum amount of pressure since the weight of the water from the surface till the bottom falls directly on the ocean floor.

The following equation is used in the calculation of liquid pressure:

Liquid pressure = ⍴×g×h

Where, 

⍴ denotes fluid density of the liquid

g denotes acceleration due to the gravity

and h denotes the depth of the liquid

Pressure in fluid mechanics

• The pressure on any surface is always exerted in the inward direction at any given surface
• Pressure is always expressed in terms of Pascal unit, i.e. Pa or N/m2     
• The standard atmospheric pressure is expressed at 14.70 psi or 101.325 kPa
• In the case of pressure in fluid mechanics, three different factors play an important role, i.e. gravity, pressure forces, and the force of friction (vicious forces)

There are mainly three different types of pressure:

• Absolute pressure – The absolute pressure is measured at pressure level zero. Hence, absolute pressure can also be considered as the perfect vacuum. The letter p denotes the absolute pressure, and it is almost similar to the thermodynamic pressure

• Gauge pressure – The gauge pressure, commonly called overpressure, is always measured relative to the atmospheric pressure. Hence, in the case of a perfect vacuum where the atmospheric pressure is at zero, the gauge pressure will be the same as well

The gauge pressure is denoted by the expression: pg = pabs-patm 

• Vacuum pressure – The vacuum pressure is always calculated when the gauge pressure is at a negative connotation and it is also measured relative to the absolute pressure

In situations when there is absolutely no acceleration in the liquid, the pressure of the liquid becomes solely dependent on the force of gravity. And, due to absolutely no acceleration in the liquid, the pressure is balanced by gravity to an absolute zero. This phenomenon is known as hydrostatics or fluid statics.

Conclusion

Pressure due to a fluid column depends on various factors that affect the amount of pressure exerted on the surface and the container of the fluid material. The factors responsible for the exertion of pressure by the fluid are- acceleration of the fluid matter, gravity and the weight and density of the fluid.

Pressure at the deepest depth of the liquid in a column is always greater than the pressure at the surface level because the liquid at the bottom of a container has to carry the weight of the liquid from the surface to the bottom.