Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 20 - Think and Discuss: 87

Answer

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.
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