Fluid Statics | Civil Engineering SSC JE (Technical) - Civil Engineering (CE) PDF Download

Chapter 2

Fluid Statics

 Pascal's Law

  • The intensity of pressure at any point in a stationary fluid is same in all directions.
    px = py = pz

Note that pressure varies only with depth in stationary fluids, whereas if fluids is in motion, pressure may vary in horizontal directions also.

  • Fluid pressure is measured in Force/ Area and it is expressed in Pascal (N/m 2) or Bar. 1 Bar = 105 N/m2 1 MPa = 10 Bar. For static fluids, piezo-metric head is constant throughout the fluid.

Fluid Statics | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Fluid Statics | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
 
Pressure Scales (i) Absolute Scale

  • Pressure is measured with reference to absolute zero. In this scale pressure cannot be negative. Minimum pressure is zero.
  • Abs. pressure = Pguage + local atm. pressure

(ii) Gauge Scale: Pressure is measured with reference to atmospheric pressure. It means atmospheric pressure is taken zero. Gauge pressure can be positive, negative or zero.

  • Gauge pressure = Absolute pressure – local atmospheric pressure
  • Vacuum pressure = local atmospheric pressure – absolute pressure
  • The atmospheric pressure varies with altitude, temperature and local conditions. It is measured by Barometer.
  • At mean sea level atmospheric pressure is 1.01 × 105 Pascal or 1 Bar or 10.3 mts. of height of water or 76 cm height of mercury.
     

Pressure Measuring Devices:

(i) Piezometer: It is simple graduated glass tube which measures pressure in gauge scale. The height up to which liquid is raised in this tube is called pressure head. It is useful for small pressure measurement and is not suitable for high pressure and negative pressure measurements. p = gh; where 'h' is height of liquid column

(ii) Manometer It is based on liquid column balance mechanism. The manometric liquid used should have high density & low vapour pressure.

(a) Simple Manometer or U-tube Manometer.
It can measure both positive and negative pressures.
(b) Differential Manometer.
It measures difference in pressure between two points.

 Fluid Statics | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

(c) Micromanometer : It measures small difference of pressure. It is modified form of Simple Manometer whose one  limb is made of larger cross section area.

(d) Inclined Manometer : It measures small pressure low velocity gas flow.

 Fluid Statics | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

p = S gw
sin q =gℓ sinq
S = specific gravity of liquid
gw = specific weight of water
g = specific weight of manometric liquid

(iii) Mechanical Gauges: These are used for rough measurement of high pressure. These are based on spring balance mechanism. Ex. Bourdon tube pressure gauge.

(iv) Aneroid Barometer or Mercury Barometer: It is used to measure local atmospheric pressure on absolute scale.

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FAQs on Fluid Statics - Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

1. What is fluid statics in civil engineering?
Fluid statics in civil engineering is a branch of fluid mechanics that deals with the behavior of fluids at rest. It focuses on understanding the forces exerted by fluids on solid surfaces and the equilibrium conditions of fluids in containers or structures.
2. How is fluid pressure calculated in fluid statics?
Fluid pressure in fluid statics can be calculated using the formula: pressure = force/area. This means that the pressure exerted by a fluid is directly proportional to the force applied and inversely proportional to the area over which the force is distributed.
3. What is the significance of fluid statics in civil engineering?
Fluid statics is significant in civil engineering as it helps engineers analyze and design various hydraulic structures such as dams, pipelines, and water tanks. By understanding the behavior of fluids at rest, engineers can ensure the stability and safety of these structures.
4. How does the shape of a container affect fluid statics?
The shape of a container affects fluid statics by influencing the distribution of fluid pressure. For example, a container with a wide base and narrow top will have a higher pressure at the bottom due to the greater weight of the fluid above. Engineers consider the shape of containers when designing structures to ensure proper load distribution.
5. What are some real-life applications of fluid statics in civil engineering?
Fluid statics finds application in various civil engineering projects. For instance, it is used to analyze the stability of retaining walls, calculate the forces acting on submerged structures like piers and docks, and design efficient water distribution systems. Additionally, fluid statics helps in determining the buoyant forces acting on submerged objects such as ships and underwater pipelines.
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