Coefficient Of Viscosity Using Terminal Velocity — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Coefficient of Viscosity using Terminal Velocity Determining viscosity of highly viscous fluids like glycerin or castor oil using Stokes Law. Identify forces acting on the sphere: Weight (down), Buoyancy (up), and Viscous drag (up). Viscous drag is given by Stokes Law: F = 6πηrv. At terminal velocity, Net Force = 0. Weight = Buoyancy + Viscous Drag. Substitute volumes: (4/3)πr³ρg = (4/3)πr³σg + 6πηrv. Rearrange and solve for η. Liquid must be of infinite extent (no wall effects) Motion must be streamlined/laminar (Low Reynolds number) Body must be perfectly spherical and rigid Liquid must be homogeneous and incompressible Ignoring liquid density: The buoyant force is significant and σ cannot be ignored if ρ is comparable. Terminal velocity timing: It is assumed velocity is measured only after it becomes constant. Wall effects: In real lab cylinders, the container diameter must be much larger than the ball diameter.