Source: https://guthlabs.ai/docs/instruments/stokes-law-settling-velocity-calculator/mechanism/

instrument mechanism / verified-clean

# Stokes' Law Settling Velocity Calculator mechanism

The inspectable method record for Stokes' Law Settling Velocity Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The velocity formula is correct under the stated physical assumptions, but the specification is incomplete because g, the Reynolds-number formula, and the exact validity threshold are unspecified. Resolve those ambiguities before release.

- The settling-velocity formula is standard for a spherical particle in the creeping-flow regime, assuming SI units and gravitational acceleration g=9.80665 m/s².

- The specified validity check has no formula. Reynolds number should be Re=(rho_f·|V|·d)/mu=(2·rho_f·|V|·r)/mu, with the absolute velocity used for rising particles.

- The claimed validity threshold is ambiguous: the output says Re<1 while the honest label says Re<~1; the instrument should define an exact threshold and labeling behavior.

- The formula permits a negative velocity when rho_p<rho_f, which represents rising rather than settling; this sign convention must be documented.

## Units and conventions

- Particle radius is in meters, densities are in kg/m³, dynamic viscosity is in Pa·s (equivalent to kg/(m·s)), velocity is in m/s, and g is assumed to be 9.80665 m/s².

- The viscosity table must identify dynamic viscosity and its temperature/pressure conditions; kinematic viscosity in m²/s cannot be substituted without conversion.

- Reynolds number uses fluid density, particle diameter 2r, absolute velocity, and dynamic viscosity.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "particle_radius_m": 0.00001,
    "particle_density_kg_per_m3": 2650,
    "fluid_density_kg_per_m3": 1000,
    "dynamic_viscosity_Pa_s": 0.001,
    "g_m_per_s2": 9.80665
  },
  "expected_outputs": {
    "settling_velocity_m_per_s": 0.0003595771667,
    "reynolds_number": 0.007191543333,
    "stokes_valid": true
  },
  "working": "Delta rho = 2650 - 1000 = 1650 kg/m³. r² = (0.00001)² = 1.0×10^-10 m². V = (2/9)×1650×9.80665×1.0×10^-10/0.001 = (2/9)×1.61809725×10^-6/0.001 = 3.595771667×10^-4 m/s. Re = 2×1000×3.595771667×10^-4×0.00001/0.001 = 0.007191543333. Since Re<1, the Stokes check passes."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

Zero viscosity produces division by zero in the settling-velocity formula and Reynolds-number calculation. The instrument specification does not state an input-rejection rule, so this case must be handled as undefined rather than converted to a numeric result.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/stokes-law-settling-velocity-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/stokes-law-settling-velocity-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/stokes-law-settling-velocity-calculator/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`