The speed of sound in air at sea level is approximately 343 meters per second (m/s) or about 1,235 kilometers per hour (km/h, 767 mph) at a temperature of 20°C (68°F). This is the generally accepted standard value used in many applications such as physics and engineering.
Speed of Sound Calculator (Air at Sea Level)
What is the Speed of Sound?
The speed of sound is the distance a sound wave travels per unit time as it moves through a medium, such as air. It represents how fast vibrations or pressure disturbances move through that medium. Sound travels as mechanical waves that require a medium to propagate, and its speed depends heavily on the properties of that medium.
How is the Speed of Sound in Air Determined?
The speed of sound in air primarily depends on the temperature of the air. Higher temperatures allow air molecules to move faster, making sound waves travel quicker. At sea level atmospheric pressure (about 101.325 kPa) and standard room temperature 20°C, the speed is about 343 m/s. At 0°C, the speed is slower, approximately 331 m/s.
Factors Affecting Speed of Sound in Air at Sea Level:
- Temperature: The biggest influence. For every degree Celsius increase, the speed of sound increases by roughly 0.6 m/s.
- Humidity: More humid air is less dense than dry air, allowing sound to travel faster.
- Altitude/Pressure: While the speed depends mainly on temperature, air pressure variations at sea level have minimal effect because the density and elasticity change proportionally.
- Medium Composition: The type of gas impacts speed; sound travels slower in denser gases and faster in lighter gases.
Common Values and Variations
| Temperature (°C) | Speed of Sound (m/s) | Speed of Sound (mph) |
|---|---|---|
| 0 | 331 | 740 |
| 15 (standard sea level) | 340 | 761 |
| 20 | 343 | 767 |
| 30 | 349 | 780 |
Thus, the often-quoted value of 343 m/s is a useful benchmark for sound speed at sea level and room temperature conditions.
Why Does the Speed of Sound Change with Altitude?
Sound speed reduces at higher altitudes mainly due to decreasing temperature. Even though the air density reduces with altitude (which might suggest faster sound), the dominant effect of temperature drop is generally a slower sound speed. For example, at 30,000 feet altitude, the speed of sound is approximately 301 m/s (678 mph).
Mach Number and Speed of Sound
The speed of sound is a critical baseline in aeronautics and aviation. The Mach number is the ratio of an object’s speed to the speed of sound in the surrounding medium. For instance, flying at Mach 1 means flying at the speed of sound. At sea level, Mach 1 is around 343 m/s or 761 mph.
Speed of Sound in Other Media for Comparison
While sound travels at about 343 m/s in air at sea level, it travels much faster in liquids and solids due to their greater density and elasticity. For example:
- In seawater, sound travels at roughly 1,500 m/s, about 4.3 times faster than in air.
- In steel, the speed of sound is about 5,960 m/s.
Real-World Applications and Implications
- Weather Forecasting: Thunderstorm distances are estimated by timing lightning thunder and using the speed of sound.
- Engineering: Aviation, sonar, and acoustic device calibration rely on accurate sound speed values.
- Acoustics: Soundproofing and architectural design incorporate sound speed to predict sound travel and echo behavior.
Summary
- The speed of sound in air at sea level and at 20°C is about 343 m/s (1,235 km/h or 767 mph).
- It varies mainly with temperature, and to lesser extents with humidity, pressure, and air composition.
- It is slower at higher altitudes due to lower temperatures.
- Speed of sound is fundamental in fields such as aviation, meteorology, and acoustics.
This understanding of sound speed at sea level forms the basis for many scientific, industrial, and everyday applications related to sound propagation.