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The speed of sound in a gas is $v = \sqrt{\gamma P/\rho} = \sqrt{\gamma RT/M}$, derived from Laplace's adiabatic correction to Newton's isothermal formula. Key dependencies:

Temperature: $v \propto \sqrt{T}$ (absolute temperature). At 0 degrees C: $v \approx 331$ m/s in air. Near room temperature: $v \approx 331 + 0.6t$ m/s (linear approximation). A 1% temperature change causes about 0.5% speed change.

Pressure: At constant temperature, $P/\rho = RT/M$ is constant, so changing pressure alone does NOT change the speed of sound. This counterintuitive result is frequently tested.

Humidity: Moist air has lower average molar mass (water vapor $M = 18$ replaces heavier N$_2$ at $M = 28$), so $v$ increases. Moist air is lighter than dry air — a fact many students get wrong.

Gas type: $v \propto 1/\sqrt{M}$. Lighter gases (H$_2$, He) transmit sound faster. $v_{\text{H}_2}/v_{\text{O}_2} = \sqrt{32/2} = 4$.

Medium comparison: Sound travels fastest in solids (strong intermolecular forces), slower in liquids, slowest in gases. In steel: $\approx 5000$ m/s. In water: $\approx 1500$ m/s. In air: $\approx 340$ m/s.