Fluids in Motion (Hydrodynamics) — A/L Physics

What must I remember about Fluids in Motion (Hydrodynamics)?

• Real Fluid Flow & Viscosity: Viscous friction arises from molecular cohesive forces between adjacent shearing fluid layers; Newton's Law of Viscosity: Viscous drag force F = -η A (dv/dx), where η is viscosity coefficient and dv/dx is velocity gradient.
• Poiseuille's Formula for Laminar Flow: Volume flow rate Q through capillary tube of radius r and length L under pressure difference ΔP: Q = (π r⁴ ΔP) / (8 η L).
• Stokes' Law: Viscous drag force on a smooth spherical particle of radius r moving at slow velocity v in fluid of viscosity η: F_d = 6 π η r v.
• Terminal Velocity: As falling sphere accelerates, drag force F_d and upthrust U increase until net force is zero; Terminal Velocity v_t = [2 r² (ρ_solid - ρ_fluid) g] / (9 η).

Test yourself (1 minute)

1. Dependence on radius in Poiseuille flow

   Q is extremely sensitive to tube radius: doubling radius increases flow rate 16-fold (r⁴ dependence).

2. Temperature dependence of Viscosity

   For liquids, viscosity decreases with increasing temperature (weakened intermolecular cohesive bonds); for gases, viscosity INCREASES with temperature (increased molecular collisions).

3. Reynolds Number (Re)

   Dimensionless flow regime predictor: Re = (ρ v d) / η; Re < 2000 indicates laminar flow, Re > 3000 indicates turbulent flow.

Practise Fluids in Motion (Hydrodynamics) questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 2: Mechanics & Fluid Dynamics

What should I study first?

Next in the syllabus

Where does Fluids in Motion (Hydrodynamics) fit in the syllabus?

Unit 2.8 · Year 1 · Term 1