Compute the speed of sound in air from the air temperature.
干空气中声速随温度近似线性增加。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Speed of sound in air | v ≈ 331.4 + 0.6·T (m/s, T in °C); exact form v = sqrt(γRT/M) | Laplace sound-speed formula / ISO 9613-1 |
Constants used on this page and their authoritative sources, for verification and citation
| Constant | Value | Unit | Source |
|---|---|---|---|
| Molar gas constant R | 8.314462618 | J·mol⁻¹·K⁻¹ | New SI (derived from exact N_A·k) |
| Mean molar mass of dry air M | 28.96546e-3 | kg·mol⁻¹ | CIPM 2007 recommendation (ISO 2533 older value 28.9647e-3) |
| Ratio of specific heats for dry air γ | 1.400 | — | Common engineering approximation (dry air, 0–100 ℃) |
| Celsius scale zero point T_0 | 273.15 | K | SI / ITS-90 defining value (exact) |
| Speed of sound in dry air at 0 ℃ | 331.3 | m·s⁻¹ | Derived from c = √(γRT/M) (consistent with ISO 9613-1) |
Note: v = 331.3 + 0.606·T(℃) is a dry-air linear approximation valid only near room temperature; humidity raises the speed noticeably (water vapour has M = 18 g/mol, so humid air is lighter).