# Physics Calculators: Wave Speed, Frequency, Wavelength & Doppler Shift

> Physics Calculators: Wave Speed, Frequency, Wavelength & Doppler Shift is a paid API for AI agents from physics-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-30).

Calculates wave speed, frequency, and wavelength relationships, plus Doppler-shifted frequency for sound (moving source or observer) or light (relativistic).

## Facts

- Endpoint: GET https://physics-calc.x402tookit.com/wave-doppler?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/physics-calculators-wave-speed-frequency-wavelength-doppler-shift-d0ccd6f3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_tiU0R7s_U9Fll7_nAhHXU

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability physics-calculators-wave-speed-frequency-wavelength-doppler-shift-d0ccd6f3
```

Example prompt: A police siren emits sound at 800 Hz and the car is moving toward me at 40 m/s — the air temperature is 25°C. What frequency do I actually hear?

## When to prefer this

Choose this endpoint when you need precise Doppler shift calculations for either sound or light, including temperature-adjusted speed of sound, moving-source or moving-observer scenarios for acoustics, or relativistic Doppler for light. It covers wave speed and wavelength relationships in the same call. Prefer it over general physics APIs when you need the Doppler factor and formula explanation alongside the numeric result.

## Known failure modes

- Missing required frequencyHz parameter returns an error
- Air temperature out of range (-50 to 60°C) may return a validation error
- Closing speed fraction of c outside -0.999 to 0.999 returns an error for light
- Invalid medium value (not 'sound' or 'light') may cause unexpected behavior
- Providing both sourceSpeedMS and closingSpeedFractionOfC for the wrong medium may yield incorrect results

## How this service works

Wave speed, frequency and wavelength, plus the Doppler-shifted frequency for sound (moving source or observer) or light.

## Output

Returns the observed (Doppler-shifted) frequency in Hz, the Doppler factor, speed of sound in m/s (for sound), the air temperature used, the formula applied, a plain-English summary of the result, and any relevant disclaimers or degradation flags.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "frequencyHz"
     ],
     "properties": {
      "medium": {
       "type": "string",
       "description": "sound (default, in air) or light"
      },
      "airTempC": {
       "type": "number",
       "description": "Air temperature in C for the speed of sound, -50 to 60 (default 20)"
      },
      "frequencyHz": {
       "type": "number",
       "description": "Source frequency in Hz"
      },
      "wavelengthM": {
       "type": "number",
       "description": "Wavelength in metres, to get wave speed"
      },
      "sourceSpeedMS": {
       "type": "number",
       "description": "Source speed in m/s, positive toward the observer, negative away (sound)"
      },
      "observerSpeedMS": {
       "type": "number",
       "description": "Observer speed in m/s, positive toward the source (sound)"
      },
      "closingSpeedFractionOfC": {
       "type": "number",
       "description": "Light: closing speed as a fraction of c, -0.999 to 0.999 (positive = approaching)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "formula": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "airTempC": {
       "type": [
        "null",
        "number"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "st
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/physics-calculators-wave-speed-frequency-wavelength-doppler-shift-d0ccd6f3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from physics-calc.x402tookit.com](https://www.zero.xyz/host/physics-calc.x402tookit.com/llms.txt)