Physics

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Stokes' Law Calculator.

Calculate the terminal velocity of a small spherical particle in a viscous medium.

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Results update as you type.

Terminal velocity: 92.618361 m/s

Terminal velocity

0.000000m/s

Results update automatically as you type.

Educational model. Inputs and assumptions are explicit; verify engineering or scientific decisions independently.

Use Cases

Sedimentation Analysis

Determine how fast particles settle in a liquid or gas, useful in environmental engineering, water treatment, and soil science.

Example: Estimate settling velocity of silt particles in a water column.

Aerosol Particle Behavior

Predict the falling speed of small droplets or dust in air, aiding in air quality modeling and inhalation studies.

Example: Calculate terminal velocity of a 10 µm water droplet in air.

Frequently Asked Questions

What is Stokes' Law and when does it apply?
Stokes' Law describes the drag force on a small sphere moving through a viscous fluid at low Reynolds numbers (laminar flow). It applies to particles that are small, spherical, and moving slowly relative to the fluid, such as fine dust settling in air or cells in water.
How do I calculate terminal velocity using this calculator?
Enter the particle's radius, particle density, fluid density, and fluid viscosity. The calculator uses Stokes' Law to compute the terminal velocity, which is the constant speed reached when gravitational force equals the drag force and buoyancy.
What units should I use for the inputs?
Use consistent units: radius in meters, densities in kg/m³, and viscosity in Pa·s. The calculator will output terminal velocity in m/s. Ensure all inputs are in the same unit system to get accurate results.

Tips & Common Mistakes

Tips

  • Ensure the particle is spherical and small enough for laminar flow; Stokes' Law assumes Reynolds number less than about 0.1.
  • Use consistent units (SI recommended) to avoid conversion errors.
  • For non-spherical particles, the result is approximate; consider shape correction factors.
  • Check that the fluid is Newtonian and homogeneous; otherwise, the law may not apply.

Common Mistakes to Avoid

  • Using diameter instead of radius; always input the radius of the sphere.
  • Forgetting to subtract fluid density from particle density when calculating buoyancy.
  • Using viscosity in centipoise without converting to Pa·s (1 cP = 0.001 Pa·s).

Last updated: August 13, 2026