## Conceptual Physics (12th Edition)

Using the hint, in the air mixture, all the molecules have the same temperature and average kinetic energy, $\frac{1}{2} mv^{2}$. Therefore, at the same temperature, lighter water vapor molecules (smaller m) are moving faster (higher v) than the more massive diatomic nitrogen and oxygen molecules (larger m, smaller v). In moist air, the more numerous water vapor molecules bump into each other more frequently, meaning a sound wave (which is transmitted via bumping between particles in the medium) travels more rapidly.