Source: https://guthlabs.ai/docs/instruments/drag-force-drag-coefficient-calculator/implementation/

instrument implementation / implementation-contract

# Drag Force / Drag Coefficient Calculator implementation

A source-bound implementation contract for Drag Force / Drag Coefficient Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t7-086

**Effect**: Computation or source lookup only

## Input and validation requirements

The inverse-Cd calculation is undefined when frontal area is zero and must reject the input. The signed-velocity case also exposes an ambiguity: the scalar V² formula gives only drag magnitude, while force direction and signed versus magnitude-only drag power require an explicit convention.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "mode": "forward_drag",
    "shape": "sphere",
    "Cd": 0.47,
    "frontal_area_m2": 0.01,
    "velocity_m_per_s": 10,
    "fluid_density_kg_per_m3": 1.225
  },
  "expected_outputs": {
    "drag_force_N": 0.287875,
    "drag_power_W": 2.87875
  },
  "reference_data": {
    "Cd_sphere": 0.47,
    "Cd_source_convention": "widely tabulated standard value for a smooth sphere in common subcritical flow; actual value depends on Reynolds number",
    "air_density_kg_per_m3": 1.225,
    "air_density_source_convention": "ISO 2533 standard atmosphere, rounded textbook sea-level value at 15 C and 101.325 kPa"
  },
  "working": "Fd = 0.5*rho*V^2*Cd*A = 0.5*1.225*(10^2)*0.47*0.01 = 0.6125*100*0.47*0.01 = 61.25*0.47*0.01 = 28.7875*0.01 = 0.287875 N. P = Fd*V = 0.287875*10 = 2.87875 W."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/drag-force-drag-coefficient-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/drag-force-drag-coefficient-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/drag-force-drag-coefficient-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-tranche7/tranche7-results.json`