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Fluid Mechanics Formulas

You may feel Solving the Fluid Mechanics Problems almost an impossible task. Luckily, you need not bother anymore as we have curated the complete list of Fluid Mechanics Formulas here. Formula Sheet of Fluid Mechanics covers numerous formulas on Pascal's Law, Absolute Pressure and Gauge Pressure, Archimede’s Principle, etc. Apply the Fluid Mechanics Formulae provided here and arrive at the solutions easily. For more concepts of Physics and related guidance check out the Physics Formulas provided by us.

List of Fluid Mechanics Formulae

1. Pressure inside the liquid

The pressure due to liquid act on the surface below depth h is given by
P = hρg
where p is the density of liquid and g acceleration due to gravity.

2. Pascal’s law

According to Pascal’s law the pressure at every point inside the liquid is same in the absence of gravity.

3. Absolute pressure & gauge pressure

  • Absolute pressure at a point A is the total pressure at that point including the pressure of liquid and that of atmosphere.
  • Gauge pressure is the relative pressure between two points of which one is at the surface and other is at some distance below inside the liquid. Thus

Fluid Mechanics formulas img 1
Pabsolute = PGauge + Patmospheric, Pgauge = ρgh
Pabs = ρgh + P0

4. Archimede’s principle

It states that when a body is immersed wholly or partly in a liquid at rest, it losses some of its weight. The loss in weight of the body in the liquid is equal to the weight of the liquid displaced by the immersed part of the body. Let the true weight of the body be Wb then
Wb = Mbg = Vbρbg
weight of the liquid displaced
WL = mLg = VLρLg
Then observed weight of the body
W = Wb – WL
= (Vbρb – VLρL)g

5. Laws of flotation

If ρb → density of the body & ρL → density of the liquid. Then
Case I
ρb > ρL the body will sink to the bottom of the liquid.

Case II
ρb < ρL the body will rise above the surface of liquid to such an extent that the weight of the liquid displaced by immersed part of the body becomes equal to the weight of the body.

Case III
ρb = ρL In this the resultant force acting on the body fully immersed in liquid is zero, The body is at rest anywhere within the liquid.

(B) Hydrodynamics

6. Critical velocity

The critical velocity is that velocity of liquid flow, upto which its flow is streamlined and above which its flow becomes turbulent.
vc = \(\frac{N_{R} \eta}{\rho D}\)
NR → Reynold Number.
η → Cofficient of viscosity,
ρ → density of liquid.
D → Diameter of the tube.

7. Physical significance of NR

  • If the value of Reynold number lies between 0 to 2000, the flow of liquid is stream line or laminar.
  • For value of NR above 3000, the flow of liquid is turbulent.
  • For value of NR between 2000 to 3000, the flow of liquid is unstable changing from stream line to turbulent.

8. Equation of continuity
Fluid Mechanics formulas img 2
A1V1 = A2 v2 = v/t
A v = constant

9. Bernoulli’s equation

It is a mathematical expression of the law of conservation of mechanical energy in fluid dynamics. Every point in an ideal fluid flow is associated with three kinds of energy.
(i) Kinetic energy per unit volume at a point.
\(\frac{\mathrm{K.E.}}{\mathrm{Volume}}=\frac{1}{2} \rho \mathrm{v}^{2}\)

(ii) Potential energy per unit volume at a point with respect to an assumed datum is
\(\frac{\text { P.E. }}{\text { Volume }}=\rho g h\)

(iii) Pressure energy per unit volume at a point.
\(\frac{\text { Pressure Energy }}{\text { Volume }}=\mathrm{P}\)

According to conservation of energy flow, the sum total of these energy remains constant along a stream line in a steady flow of an ideal liquid.
\(\frac{1}{2}\) ρv2 + ρgh + P = constant ← Bemoullis equation.
Fluid Mechanics formulas img 3

10. Torricelli’s theorem

According to this theorem, velocity with which the liquid flows out of on orifice (i.e. a narrow hole) is equal to that which a freely falling body would acquire in falling through a vertical distance equal to the depth of orifice below the free surface of liquid.
v = \(\sqrt{2 \mathrm{gh}}\)

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