Mechanical Properties of Fluids NEET Notes: Concise Guide & Formulas

Mechanical Properties of Fluids

Pressure, viscosity, surface tension, Bernoulli — simplified for NEET. Learn concepts that matter.

🔹 Fluid Pressure 🔹 Pascal's Law 🔹 Archimedes 🔹 Bernoulli 🔹 Viscosity 🔹 Surface Tension

📘 What you'll learn: key formulas, 3 solved examples, quick revision, exam tips

🔍 Core concepts (simple)

🧪 Fluid Pressure

Pressure = F/A. In a fluid at rest, pressure increases with depth: P = P₀ + ρgh. Same at all points at same horizontal level.

⚖️ Pascal's Law

Pressure applied to an enclosed fluid is transmitted undiminished to every part. Used in hydraulic lifts: F₁/A₁ = F₂/A₂.

🌊 Archimedes' Principle

Buoyant force = weight of displaced fluid. A body floats if average density ≤ fluid density.

✈️ Bernoulli's Theorem

For ideal fluid, P + ½ρv² + ρgh = constant. Explains lift, venturi effect.

🧴 Viscosity

Internal friction in fluids. Newton's law: shearing stress = η (dv/dy). η = coefficient of viscosity (poiseuille, poise).

💧 Surface Tension

Elastic tendency of liquid surface. S = F/L (N/m). Excess pressure inside drop = 2S/r, inside bubble = 4S/r. Capillary rise: h = 2S cosθ / (ρgr).

📐 Quick formula sheet

Pressure at depth P = P₀ + ρgh

Hydraulic lift F₂ = F₁ × (A₂/A₁)

Buoyancy F_b = ρ_fluid V_imm g

Bernoulli P + ½ρv² + ρgh = const

Viscous force F = η A (dv/dx)

Surface tension S = F/L

Capillary rise h = 2S cosθ/(ρgr)

Excess pressure (drop) ΔP = 2S/r

✏️ Solved examples (NEET level)

Example 1 (Hydrostatic pressure)

A 20 m deep lake. Find pressure at bottom. (ρ = 1000 kg/m³, Pₐ = 1.01×10⁵ Pa, g=10)

Step 1 P = Pₐ + ρgh = 1.01×10⁵ + 1000×10×20

Step 2 = 1.01×10⁵ + 2×10⁵ = 3.01×10⁵ Pa

Answer: 3.01×10⁵ Pa

Example 2 (Bernoulli)

Water flows at 2 m/s in a horizontal pipe (P₁=4×10⁴ Pa). At a constriction, speed is 4 m/s. Find P₂ (ρ=1000).

Step 1 Bernoulli: P₁ + ½ρv₁² = P₂ + ½ρv₂² (h same)

Step 2 P₂ = P₁ + ½ρ(v₁² – v₂²) = 4×10⁴ + ½×1000×(4 – 16)

Step 3 = 40000 – 6000 = 34000 Pa = 3.4×10⁴ Pa

Example 3 (Capillary rise)

A capillary tube (radius 0.5 mm) dipped in water (S=0.072 N/m, θ=0°). Find rise. ρ=1000, g=10.

Step 1 h = 2S cosθ / (ρ g r) = 2×0.072×1 / (1000×10×0.5×10⁻³)

Step 2 = 0.144 / (5) = 0.0288 m = 2.88 cm

⚡ Quick revision + mistakes & tips

✅ Points to remember: Pressure scalar, buoyancy = weight of displaced fluid, Bernoulli applies along streamline, viscosity dissipates energy.

⚠️ Common mistakes: forgetting atmospheric pressure, using diameter instead of radius in capillary, mixing gauge & absolute pressure.

🎯 Exam tips: For manometer problems, equate pressure at same horizontal level. In venturi, velocity higher → pressure lower. Memorise excess pressure formulas.

❓ Quick FAQ

What is gauge pressure?

Pressure relative to atmospheric: P_gauge = P_abs – P_atm.

Why does a needle float on water?

Due to surface tension – the weight is balanced by upward force from surface film.

What is Stokes' law?

Viscous force on sphere: F = 6πηrv. Used to find viscosity.

📥 Free handwritten notes (toppers)

🔬 Physics NEET Toppers Notes	Download
🧬 Biology NEET Toppers Notes	Download
⚗️ Chemistry NEET Toppers Notes	Download
📐 Basic Maths for NEET	Download
📏 Units & Measurements	Download
⚙️ Laws of Motion	Download
🔋 Work, Energy, Power	Download
🌍 Gravitation	Download
💨 Kinetic Theory of Gases	Download
💧 Mechanical Properties of Fluids	Download

📘 Mechanical Properties of Fluids – concise NEET notes. Last update 2026.