The speed of sound in air is most affected by variations in which factor?

• A. Sound frequency
• B. Humidity
• C. Barometric pressure
• D. Ambient temperature

Answer: (D)

The speed of sound in air is most affected by ambient temperature because temperature directly influences how quickly molecules move and how efficiently they transmit a pressure disturbance. In air, the speed of sound rises with temperature roughly following v ≈ sqrt(γRT/M); warmer air means more energetic molecules and faster transfer of the compression wave, so sound travels faster. Humidity can nudge the speed a bit because water vapor is lighter than the major components of air, which slightly lowers density, but that effect is small compared to temperature. Barometric pressure changes density too, but at a given temperature the impact on speed is minimal in practical ranges. The frequency of the sound itself doesn’t change how fast it travels through air in ordinary conditions—the medium’s speed is essentially the same across audible frequencies. So, ambient temperature is the dominant factor shaping the speed of sound in air.