Day 2 Properties of Fluids – ECET 2026 Mechanical Notes, Formulas, MCQs

Concept Notes

Fluid Mechanics deals with the behavior of liquids and gases at rest and in motion.
👉 A fluid is a substance that deforms continuously under the action of shear stress, no matter how small.
Fluids include liquids + gases.

🔹 Properties of Fluids

1. Density (ρ):
   Mass per unit volume.
   Units: kg/m³
   Example: Water at 4°C → 1000 kg/m³.
2. Specific Weight (γ):
   Weight per unit volume.
   
   Units: N/m³
3. Specific Volume (v):
   Volume per unit mass.

Specific Gravity (SG):
Ratio of density of fluid to density of water at 4°C.

Viscosity (μ):
Resistance to flow (internal friction).

• Dynamic viscosity (μ): Units → Ns/m² (Pa·s).
• Kinematic viscosity (ν):

6. Compressibility (β):
   Change in volume with pressure.

Surface Tension (σ):
Tensile force at liquid surface due to molecular attraction.
Units: N/m
Example: Water rises in a capillary tube due to surface tension.

Capillarity:
Rise or fall of liquid in a small diameter tube due to surface tension.
Capillary rise:

Vapor Pressure (Pv):
Pressure at which a liquid starts to vaporize at given temperature.
If fluid pressure < vapor pressure → cavitation occurs.

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⚙️ Formulas

1. Density:

Specific Weight:

Specific Volume:

Specific Gravity:

Kinematic Viscosity:

Bulk Modulus (Compressibility):

Capillary Rise:

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🔟 10 MCQs

Q1. Density of water at 4°C is approximately:
a) 950 kg/m³
b) 1000 kg/m³
c) 1050 kg/m³
d) 1200 kg/m³

Q2. Specific gravity is defined as:
a) Ratio of weight to volume
b) Ratio of density of fluid to density of water
c) Ratio of pressure to volume
d) Ratio of viscosity to density

Q3. If dynamic viscosity μ = 0.01 Ns/m² and density ρ = 1000 kg/m³, then kinematic viscosity ν = ?
a) 1 × 10⁻⁵ m²/s
b) 1 × 10⁻⁶ m²/s
c) 1 × 10⁻⁸ m²/s
d) 1 × 10⁻³ m²/s

Q4. The SI unit of surface tension is:
a) N/m²
b) N/m
c) Ns/m²
d) m²/s

Q5. Capillary rise is inversely proportional to:
a) Diameter of tube
b) Surface tension
c) Density
d) Gravity

Q6. Bulk modulus of incompressible fluid is:
a) Zero
b) Unity
c) Infinite
d) 1/ρ

Q7. Vapor pressure of a liquid increases with:
a) Decrease in temperature
b) Increase in temperature
c) Pressure applied externally
d) None of the above

Q8. Which property decides fluid flow resistance?
a) Density
b) Viscosity
c) Surface tension
d) Specific gravity

Q9. For water in a clean glass tube, the capillary effect observed is:
a) Rise of water
b) Fall of water
c) No change
d) Depends on temperature

Q10. Which of the following is dimensionless?
a) Specific gravity
b) Viscosity
c) Density
d) Surface tension

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✅ Answer Key

Q	Ans
1	b
2	b
3	a
4	b
5	a
6	c
7	b
8	b
9	a
10	a

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🧠 Explanations

• Q1: Density of water at 4°C = 1000 kg/m³ → (b).
• Q2: SG = ρfluid/ρwater → (b).
• Q3: ν = μ/ρ = 0.01 / 1000 = 1×10⁻⁵ m²/s → (a).
• Q4: Surface tension units = N/m → (b).
• Q5: h = 4σ cosθ / (ρ g d) → inversely ∝ diameter → (a).
• Q6: Incompressible → cannot be compressed → bulk modulus infinite → (c).
• Q7: Vapor pressure rises as temperature increases → (b).
• Q8: Flow resistance depends on viscosity → (b).
• Q9: Water wets glass → capillary rise → (a).
• Q10: SG is a ratio (no units, dimensionless) → (a).

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🎯 Motivation / Why Practice Matters

Hydraulics forms the base of fluid mechanics, and questions from fluid properties (viscosity, density, surface tension) always appear in ECET.
👉 Mastering these basics will make advanced topics (fluid statics, flow, turbines, pumps) much easier.
Consistent practice ensures speed + accuracy in exam.

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📲 CTA

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