🧪 Mechanical Properties of Fluids – Full Chapter Guide (Class 12 Physics)

Mechanical Properties of Fluids is an important chapter in Class 11 Physics (Maharashtra Board, CBSE & other boards). It covers the behavior of liquids and gases under forces, including pressure, buoyancy, surface tension, viscosity, and fluid dynamics like Bernoulli’s Principle.

🔹 1. What is a Fluid?

Fluids are substances that can flow — i.e., liquids and gases.
They take the shape of the container and exert pressure in all directions.

🔹 2. Pressure in Fluids

Formula: P = F / A (N/m² or Pascal)

Pressure in a fluid: P = hρg

h = depth
ρ = fluid density
g = acceleration due to gravity

🔹 3. Pascal’s Law

Pressure applied at any point in a confined fluid is transmitted equally in all directions.

Applications:

Hydraulic lifts
Hydraulic brakes
Press machines

🔹 4. Atmospheric Pressure & Barometer

Atmospheric pressure = 101325 Pa = 1 atm
Measured using a barometer (76 cm Hg)

🔹 5. Buoyancy and Archimedes’ Principle

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

Applications: Ships, submarines, hydrometers

🔹 6. Surface Tension

Caused by cohesive forces between molecules.
Measured in N/m
Examples: water droplets, soap bubbles

🔹 7. Viscosity

Resistance to flow due to internal friction.

Stoke’s Law: F = 6πrηv

High viscosity: honey, glycerin
Low viscosity: water, air

🔹 8. Bernoulli’s Theorem

Equation: P + ½ρv² + ρgh = constant

Applications: Aircraft lift, spray guns, venturimeter

🔹 9. Reynolds Number

Formula: Re = (ρvD)/η

Re < 2000: Laminar Flow
Re > 3000: Turbulent Flow

🧠 10. Real-life Applications

Blood flow in arteries (viscosity)
Hydraulic systems
Aircraft and automotive design
Weather forecast (pressure, fluid motion)

🔢 11. Numericals & Solved Example

Q. Calculate pressure at 10m depth in water (ρ = 1000 kg/m³)

P = hρg = 10 × 1000 × 9.8 = 98000 Pa

📘 12. Class 11 Board Exam Tips (Maharashtra Board)

Revise formulas regularly
Draw neat diagrams of barometer, venturimeter
Practice numericals daily
Prepare Pascal’s law, Bernoulli’s equation, and Archimedes’ law with applications

📚 13. Book Reference – Maharashtra State Board

Textbook: Physics Class 11 – Part 2

Pages: Chapter 5 – Mechanical Properties of Fluids (Page 63–78)

Practice all examples & exercises at end of chapter
Use reference books like Target, MTG, or Balbharati Solved Papers

🎯 Conclusion

The chapter on Mechanical Properties of Fluids teaches us about real-world fluid behavior – from blood flow to airplane flight. With good practice and understanding, students can master this topic and excel in board exams and NEET preparation.

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