# Mechanical Properties of Fluids, Class 11 Physics | SwaVid Mechanical Properties of Fluids, NCERT Class 11 Physics: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers. Canonical: https://www.swavid.com/cbse/class-11/physics/chapter/mechanical-properties-of-fluids Source: https://www.swavid.com/cbse/class-11/physics/chapter/mechanical-properties-of-fluids # Mechanical Properties of Fluids ## Formulas and definitions ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 11 Physics on SwaVid ### Fluid pressure and Pascal's principle ### Hydrostatic pressure variation ### Equation of continuity ### Bernoulli's principle ### Viscosity and Stokes' law ### Surface tension and capillarity ### Next chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 11 › Physics › Mechanical Properties of Fluids Notes written by SwaVid from the NCERT textbook. Class 11 Physics, Chapter 9. Key ideas, formulas and common mistakes. CBSE prints 20 marks for Units VII-IX together, not for this chapter alone. Short answer. This chapter explains the basic physical principles governing fluids at rest and fluids in steady motion. Students learn how pressure, viscosity, surface tension, and conservation laws dictate fluid behaviour in natural and practical systems. Source: NCERT Physics Part II (Reprint 2026-27) , Chapter 9, Mechanical Properties of Fluids Pressure is the normal force exerted by a fluid per unit area. Pascal's law states that pressure applied to an enclosed fluid is transmitted undiminished to every point of the fluid and the vessel walls. The pressure in a fluid at rest increases linearly with depth due to gravity. The gauge pressure at depth h is given by ρgh, while absolute pressure includes atmospheric pressure. For an incompressible, non-viscous fluid in streamline flow, mass is conserved along a flow tube. The product of the cross-sectional area and the fluid speed remains constant at all points. Along a streamline of an ideal fluid, the sum of pressure energy, kinetic energy per unit volume, and potential energy per unit volume is constant. This principle explains dynamic lift and the working of a venturimeter. Viscosity is the internal friction between adjacent layers of a fluid in relative motion. Stokes' law gives the viscous drag on a small spherical body moving through a fluid, which leads to a constant terminal velocity. Molecules at a liquid surface experience a net inward force, creating surface energy and surface tension. This causes excess pressure across curved surfaces and drives liquid rise or fall in capillary tubes. Try each question first. Then tap it to see the answer. By Pascal's principle, F₁ / A₁ = F₂ / A₂ F₂ = F₁ × (A₂ / A₁) = 150 × (0.8 / 0.02) F₂ = 150 × 40 = 6000 N 6000 N By the continuity equation, A₁ v₁ = A₂ v₂, which gives (π d₁² / 4) v₁ = (π d₂² / 4) v₂ v₂ = v₁ × (d₁ / d₂)² = 2.0 × (0.04 / 0.02)² v₂ = 2.0 × (2)² = 2.0 × 4 = 8.0 m s⁻¹ 8.0 m s⁻¹ For a liquid drop with one surface, excess pressure is ΔP = 2 S / r ΔP = (2 × 0.07) / 0.002 ΔP = 0.14 / 0.002 = 70 Pa 70 Pa Thermal Properties of Matter . Mechanical Properties of Solids . The 14 chapters of Class 11 Physics . CBSE does not give marks to one chapter. It prints 20 marks for Units VII-IX together (Properties of Bulk Matter; Thermodynamics; Behaviour of Perfect Gases and Kinetic Theory). Mechanical Properties of Fluids is part of that group. No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed. Thermal Properties of Matter. SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works. - Ch 9 NCERT book - 20 marks, Units VII-IX together - 3 quick checks - Confusing gauge pressure with absolute pressure . Remember that gauge pressure is P - Pₐ = ρgh. To find total or absolute pressure, always add the atmospheric pressure Pₐ. - Using the same excess pressure formula for drops and bubbles . A liquid drop has only one free surface, so excess pressure is 2S / r. A soap bubble has two free surfaces in contact with air, making the excess pressure 4S / r. - Assuming high fluid speed implies high pressure in Bernoulli's principle . 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