Speed of Sound
The speed of sound in a gas depends on temperature, pressure, and composition. In dry air at 20°C it is ~343 m/s. Mach number (v/c_sound) indicates supersonic flow.
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Thunder delay: 3 s per km ≈ speed of sound. Supersonic: Mach > 1; subsonic: Mach < 1. Sound travels faster in warm air than cold. Helium raises voice pitch (higher sound speed).
Ready to run the numbers?
Why: Sound speed determines echo timing, thunder distance, and supersonic flight. It varies with temperature and gas type.
How: v = √(γRT/M) for ideal gases. Temperature increases speed; humidity slightly increases it. Altitude affects via temperature and pressure.
Run the calculator when you are ready.
🔧 Calculation Mode
📊 Parameters
📊 Results
Speed of Sound
343.20 m/s
km/h
1235.5
mph
767.7
Temperature
20.0°C
📈 Visualizations
🌡️ Temperature vs Speed
🔬 Speed in Different Gases
💡 Insights
Speed of sound: 343.20 m/s (1235.5 km/h)
📝 Step-by-Step
Gas: Air (dry)
Temperature: 20.0°C
Humidity: 50%
Humidity correction: +0.01 m/s
Formula: c = √(γRT/M)
γ (gamma): 1.400
M (molar mass): 28.970 g/mol
T: 293.15 K
c = √(1.400 × 8.314 × 293.15 / 0.02897)
Speed of Sound: 343.20 m/s
For educational and informational purposes only. Verify with a qualified professional.
🔬 Physics Facts
v ≈ 331 + 0.6T (m/s) for air, T in °C
— Empirical
Mach 1 at sea level ≈ 343 m/s (1235 km/h)
— Standard atmosphere
5 s thunder delay ≈ 1.7 km from lightning
— Physics
Sound travels ~4× faster in water than air
— Acoustics
What is the Speed of Sound?
The speed of sound is the distance traveled per unit time by a sound wave through a medium. In air at 20°C, it's approximately 343 m/s (767 mph). It depends primarily on the medium's temperature and composition, not on pressure at normal conditions.
Temperature Effect
Higher temperature = faster sound. ~0.6 m/s per °C in air.
Medium Matters
Sound travels ~4x faster in water, ~15x faster in steel than air.
Mach Number
Mach 1 = speed of sound. Supersonic = M > 1.
❓ Frequently Asked Questions
What factors affect the speed of sound?
The speed of sound depends primarily on temperature, gas composition (molar mass and heat capacity ratio), and to a lesser extent on humidity. Higher temperatures increase speed (~0.6 m/s per °C in air). Lighter gases (like helium) transmit sound faster than heavier gases. Pressure has minimal effect at normal conditions.
Why does sound travel faster in helium than air?
Helium has a much lower molar mass (4 g/mol vs 29 g/mol for air) and a higher heat capacity ratio (γ = 1.667 vs 1.4). The speed formula c = √(γRT/M) shows that lower M and higher γ both increase speed. Sound travels ~3x faster in helium (965 m/s vs 343 m/s at 20°C), which is why voices sound higher pitched.
How does altitude affect the speed of sound?
At higher altitudes, temperature decreases (about 6.5°C per km in the troposphere), which reduces sound speed. Pressure also decreases, but pressure has minimal effect on speed. At 35,000 ft (10.7 km), temperature drops to about -56°C, reducing sound speed from ~343 m/s to ~295 m/s at sea level conditions.
What is Mach number and how is it calculated?
Mach number (M) is the ratio of an object's speed to the speed of sound: M = v/c. M < 1 is subsonic, M ≈ 0.8-1.2 is transonic, M > 1 is supersonic, and M > 5 is hypersonic. Aircraft cruising at 900 km/h (250 m/s) in air at 20°C (343 m/s) have Mach 0.73 (subsonic).
How do I calculate thunder distance from lightning?
Use the echo distance mode. Sound travels ~343 m/s in air at 20°C. If you hear thunder 5 seconds after seeing lightning, the distance is (343 × 5) / 2 = 857.5 m ≈ 0.86 km. The "/2" accounts for round-trip travel. A rule of thumb: 3 seconds ≈ 1 km (actually ~1.03 km).
Does humidity increase or decrease sound speed?
Humidity slightly increases sound speed in air. Water vapor (H₂O, 18 g/mol) has lower molar mass than dry air (29 g/mol), so humid air has lower effective molar mass. At 50% humidity and 20°C, speed increases by ~0.1-0.2 m/s compared to dry air. The effect is small but measurable.
What is the speed of sound in different mediums?
Speed varies dramatically: Air (343 m/s), Water (1500 m/s), Steel (6000 m/s), Glass (5500 m/s), Wood (3300-4000 m/s). Sound travels faster in solids because particles are closer together, allowing faster energy transfer. In gases, speed depends on temperature and molecular properties.
How accurate is the simplified formula c ≈ 331.3 + 0.606T?
This formula is accurate to within ~0.5% for air at standard pressure between -20°C and 40°C. It assumes dry air and ignores humidity. For precise calculations, use the ideal gas formula c = √(γRT/M) which accounts for gas properties. At extreme temperatures or pressures, use more sophisticated models.
📚 Official Data Sources
⚠️ Disclaimer: This calculator provides estimates based on ideal gas theory and standard atmospheric models. Actual speed of sound values may vary due to humidity, pressure variations, gas composition, and non-ideal gas effects. Calculations assume standard conditions unless otherwise specified. For critical applications (aviation, acoustics engineering, scientific research), verify results against NIST data, atmospheric models (ISA), and actual measurements. This tool is for educational and reference purposes only.
Speed of Sound in Different Gases (at 20°C)
| Gas | γ (gamma) | M (g/mol) | Speed (m/s) |
|---|---|---|---|
| Air (dry) | 1.400 | 28.97 | 343 |
| Air (humid 50%) | 1.400 | 28.85 | 344 |
| Nitrogen (N₂) | 1.400 | 28.01 | 349 |
| Oxygen (O₂) | 1.400 | 32.00 | 327 |
| Carbon Dioxide (CO₂) | 1.289 | 44.01 | 267 |
| Helium (He) | 1.667 | 4.00 | 1007 |
| Hydrogen (H₂) | 1.410 | 2.02 | 1306 |
| Argon (Ar) | 1.667 | 39.95 | 319 |
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