Contrary to the common belief, sound actually travels faster in dry air compared to moist air. The speed of sound is influenced by several factors, including temperature, humidity, and the composition of the medium through which it propagates.
In general, the speed of sound increases with increasing temperature. This is because higher temperatures lead to increased molecular motion, resulting in faster sound propagation. Dry air tends to be warmer than moist air under similar conditions, so sound waves travel faster in dry air.
Moist air contains water vapor, which has a higher molecular weight compared to the predominant gases in dry air (nitrogen and oxygen). The presence of water vapor molecules in the air slows down the propagation of sound waves. The water molecules act as obstacles, causing collisions and interactions that reduce the speed of sound.
Additionally, humidity affects the density of the air. Moist air is less dense than dry air because water vapor has a lower molecular mass than the gases in dry air. Lower air density results in a decrease in the speed of sound.
Therefore, while moist air may give the perception of carrying sound better due to increased humidity and better sound transmission qualities, the actual speed of sound is slightly slower compared to dry air under similar temperature conditions.