What are mechanical properties of fluids?

Mechanical properties of fluids describe how liquids and gases respond to forces, including their ability to flow, transmit pressure, resist motion, and show surface effects like viscosity and surface tension.

What is a fluid in physics?

A fluid is a substance that cannot resist shear stress in static condition and continuously deforms under even a small tangential force. Liquids and gases are fluids.

What is pressure in fluids?

Pressure is the normal force exerted per unit area by a fluid on any surface in contact with it, given by P = F/A.

How does pressure vary with depth in a liquid?

Pressure increases with depth according to P = P0 + ?gh, where ? is density, g is acceleration due to gravity, and h is depth.

State Pascal’s law.

Pascal’s law states that pressure applied to an enclosed fluid is transmitted equally and undiminished to all parts of the fluid and the container walls.

What are applications of Pascal’s law?

Pascal’s law is applied in hydraulic lifts, hydraulic brakes, hydraulic presses, and hydraulic jacks.

What is buoyant force?

Buoyant force is the upward force exerted by a fluid on an immersed body, opposing the weight of the body.

State Archimedes’ principle.

A body immersed in a fluid experiences an upward force equal to the weight of the fluid displaced by it.

Why do objects float or sink?

Objects float if the buoyant force equals or exceeds their weight, usually when their average density is less than the fluid density.

Viscosity is the internal resistance of a fluid to the relative motion between its layers.

Define coefficient of viscosity.

The coefficient of viscosity is the force per unit area required to maintain a unit velocity gradient between two parallel layers of a fluid.

Stokes’ law states that the viscous force on a small sphere moving in a fluid is F = 6p?rv.

What is terminal velocity?

Terminal velocity is the constant maximum velocity attained by a body falling through a viscous fluid when net force becomes zero.

Write the expression for terminal velocity.

Terminal velocity is given by v = (2r²(? - s)g)/(9?).

What is surface tension?

Surface tension is the property of a liquid surface that makes it behave like a stretched elastic membrane.

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🔩 Master Mechanical Properties of Solids
NCERT Class 11 · Chapter 9

Real PYQs from top competitive exams — filter by exam, attempt each question, track your progress and submit to see your full score report.

Attempt PYQs Study Strategy

Young's ModulusStress & StrainHooke's LawBulk ModulusElastic PE

Real PYQs

Exam Bodies

15+

Years Covered

~6%

Exam Weightage

PYQs Overview

📐

Stress & Strain — Definitions

Tensile, compressive, shear; longitudinal, volumetric, shear strain.

★★★★★

90% Frequency

🔗

Young's Modulus Y

Y = (F/A)/(ΔL/L); wire stretching numericals — highest frequency.

★★★★★

93% Frequency

💧

Bulk & Shear Modulus

B = –P/(ΔV/V); hydraulic stress; rigidity modulus G.

★★★★☆

74% Frequency

🌊

Stress–Strain Curve

Proportionality limit, elastic limit, yield point, fracture — conceptual.

★★★★★

88% Frequency

⚡

Elastic Potential Energy

U = ½ × stress × strain × volume = ½ × Y × ε² × V.

★★★★☆

72% Frequency

🔄

Poisson's Ratio

σ = –lateral strain / longitudinal strain; range and typical values.

★★★☆☆

55% Frequency

Topic Frequency

Young's Modulus 93%

Stress-Strain Curve 88%

Stress & Strain 90%

Bulk Modulus 74%

Elastic PE 72%

Poisson's Ratio 55%

Thermal Stress 62%

💡 Did You Know?

Young's modulus numerical in every JEE paper
Stress-strain curve theory — asked every NEET year
Elastic PE density = ½ × Y × ε² — asked 8× in JEE
Poisson's ratio for rubber ≈ 0.5
Thermal stress = YαΔT — classic JEE hybrid

Key Takeaways

🔑

Y = stress/strain for longitudinal deformation

Units: Pa or N/m². Higher Y = stiffer material (Steel > Copper > Rubber).

⚡

Elastic limit: material returns to original shape

Beyond plastic limit, permanent deformation occurs.

📐

Stress-strain curve: 5 key regions

Proportional → Elastic → Yield → Plastic → Fracture.

🌊

Bulk modulus for liquids and gases

B_adiabatic = γP; B_isothermal = P for ideal gas.

🧮

Elastic PE per unit volume = ½ × stress × strain

Also = ½ × Y × (strain)² = (stress)²/(2Y).

🎯

Thermal stress = YαΔT

When a rod is prevented from expanding: stress = YαΔT.

Study Strategy

Stress & Strain DefinitionsDay 1–2

All types with units. Distinguish carefully between them.

Young's ModulusDay 3

Wire problems — extension, stress, strain, energy — 20 problems.

Stress-Strain CurveDay 4

Label all regions; understand each point conceptually.

Bulk & Shear ModuliDay 5

Hydraulic stress, liquid compressibility — 15 problems.

Elastic PE & Thermal StressDay 6

Energy stored in stretched wire; thermal expansion prevention.

Attempt All PYQsDay 7

Young's modulus and stress-strain curve dominate chapter MCQs.

Mock TestDay 8

25-Q timed. Wire-stretching numericals = highest priority.

🗓️ 8-Day Chapter Plan

Day 1–2	Stress & Strain Definitions
Day 3	Young's Modulus
Day 4	Stress-Strain Curve
Day 5	Bulk & Shear Moduli
Day 6	Elastic PE & Thermal Stress
Day 7	Attempt All PYQs
Day 8	Mock Test

🧠 Pro Tip: The stress-strain curve diagram appears directly in MCQs. Memorise labels of all five regions and their physical meaning.

🚀

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50 PYQs: Mechanical Properties of Fluids – Entrance Exams

50 PYQs: Mechanical Properties of Fluids – Entrance Exams — Complete Notes & Solutions · academia-aeternum.com

Fluids—liquids and gases—behave very differently from solids, yet they govern some of the most fascinating and essential phenomena observed in nature and technology. From the quiet rise of water in plant stems to the powerful lift that enables aircraft to fly, the mechanical behavior of fluids plays a vital role in both everyday life and advanced scientific applications. Chapter 9: Mechanical Properties of Fluids introduces students to the physics that explains how fluids respond to forces,…

🎓 Class 11 📐 Physics 📖 NCERT ✅ Free Access 🏆 CBSE · JEE

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