Drag Force / Drag Coefficient Calculator implementation

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

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