Speed of Sound in Air
Compute speed of sound in air: v = 331.3 + 0.606·T (m/s).
v ≈ — m/s
Speed of sound in air: temperature dependence
For dry air at sea level, the speed of sound is well approximated by v = 331.3 + 0.606 · T(°C) m/s. At 20 °C ≈ 343 m/s; at 0 °C ≈ 331 m/s; at 35 °C ≈ 352 m/s. The general ideal-gas formula is v = √(γ·R·T / M), where γ=1.4 for diatomic air, R=8.314 J/(mol·K) is the universal gas constant, M=0.029 kg/mol is the molar mass of air, and T is absolute temperature in kelvin. Sound does not propagate in vacuum — it needs a material medium. Mach 1 equals the local sound speed, which depends on altitude and temperature. Lightning trick: divide the seconds between flash and thunder by 3 to get distance in km (sound travels ~1 km every 3 s).
Applications: music, sonar and aviation
Sound speed shapes musical instruments (organ pipes, flutes — pitch depends on temperature, why orchestras tune after warming up), sonar in submarines, medical ultrasound (~1.5 MHz in soft tissue), supersonic aviation (sonic booms when crossing Mach 1), and architectural acoustics (concert hall reverberation times).
FAQ
Does humidity affect sound speed? Yes, slightly — humid air is less dense, so sound travels a bit faster. The effect is small (~0.4% at 100% humidity vs dry).
Why is sound faster in water? Water is denser but also far stiffer (less compressible). Speed in water is ~1480 m/s; in steel ~5000 m/s — stiffer media beat denser ones.
Does altitude matter? Indirectly — temperature drops with altitude (about 6.5 °C per km in the troposphere), reducing sound speed. Pressure alone doesn't affect it for an ideal gas.
How fast is Mach 2? Twice the local sound speed. At sea level around 20 °C, Mach 2 ≈ 686 m/s ≈ 2470 km/h.
Related Tools
Mach Number from Temperature
Compute local sound speed from temperature and Mach number M = v/a.
Speed of Sound by Temperature
Calculates the speed of sound in air (m/s) versus Celsius temperature using 331.3+0.606·T.
Cycling Cadence to Speed Calculator
Computes cycling speed from cadence (rpm), chainring, cassette teeth and wheel diameter.
3D Print Max Speed from Volumetric Flow
Layer height, line width and the hotend flow limit in mm3/s give the speed ceiling: flow / (height x width). At 15 mm3/s and 0.2 x 0.4 mm, 187.5 mm/s.
Greenshields Speed
Calculate the speed of a traffic stream by the linear Greenshields model, v = v_f·(1 − k ÷ k_j), from the free-flow speed v_f, the current density k and the jam density k_j (vehicles/km). The result, in the unit of v_f, shows speed falls linearly with density: on an empty road (k = 0), vehicles travel at free-flow speed; as density rises, speed decreases, reaching zero at total jam (k = k_j). It is the most classic macroscopic traffic flow model, the basis of the parabolic flow-density relationship. Enter the free-flow speed, the current density and the jam density.
Railway Curve Maximum Speed
Calculate the maximum allowable speed on a railway curve, V = √(127·R·(h_a + I) ÷ B), from the curve radius R (m), the applied cant h_a (mm), the allowable cant deficiency I (mm) and the gauge B (mm). It is the inverse of curve design: given an existing curve (radius and cant) and the permitted deficiency, it finds the maximum speed trains can run safely and comfortably. Speed is limited because above it the cant deficiency would exceed the allowable — passengers would feel excessive lateral force and wheel-rail wear and risk would rise. This is fundamental in railway operation: it defines each section's maximum speeds (line speed profile) and travel time. Raising speed on existing curves needs more cant (limited), more allowed deficiency (tilting trains) or, ultimately, larger-radius regrading — an expensive work. Enter the radius, applied cant, allowable deficiency and gauge.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.