Enter your Particle Diameter, Particle Density, Medium Density, and Dynamic Viscosity (or pick a preset Medium Type) to calculate the Terminal Settling Velocity of a particle falling through a fluid — plus the Reynolds Number and a handy check on Stokes Law Validity to confirm which flow regime you're actually in.
Terminal Settling Velocity
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Terminal Velocity
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Reynolds Number
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Stokes Law Validity
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Stokes' law describes the drag force acting on spherical particles moving through a viscous fluid at low Reynolds numbers. It's fundamental for calculating terminal settling velocity of particles in air or liquid.
Use the Stokes' law formula: v = gd²(ρp - ρm)/(18μ), where g is gravity, d is particle diameter, ρp is particle density, ρm is medium density, and μ is dynamic viscosity.
Terminal velocity is the maximum constant speed a particle reaches when falling through a fluid. At this point, the gravitational force equals the drag force, resulting in zero acceleration.
Stokes' law is valid for spherical particles at low Reynolds numbers (Re < 1), in the laminar flow regime. For higher Reynolds numbers, other drag equations should be used.
Settling velocity depends on particle size, particle density, fluid density, fluid viscosity, and gravitational acceleration. Larger, denser particles settle faster in less viscous fluids.
Temperature affects fluid density and viscosity. Higher temperatures typically decrease viscosity and density, which can increase settling velocity for particles in gases and most liquids.
At 25°C, air density is approximately 1.184 kg/m³ and dynamic viscosity is 1.849×10⁻⁵ Pa·s. At standard temperature and pressure (STP), air density is 1.292 kg/m³.