

How, then, does a penguin find its mate among the huddled thousands?
The answer is in this chapter.
After diving into the water and eating, an emperor penguin must crawl back onto its home ice flow and return to its mate. In the winter, however, that mate can be anywhere among thousands of penguins huddled tightly together to avoid freezing in the harsh weather of the Antarctic, where temperatures can be −40°C and wind speeds 300 km/h. Besides, penguins all look about the same, even to other penguins, and so a penguin cannot visually recognize its mate.

Fig. 17-1 This image of a 6-month-old fetus is made with ultrasound (which has a frequency above your hearing range).
17-1 What Is Physics?
The physics of sound waves is the basis of countless studies in the research journals of many fields. Here are just a few examples. Some physiologists are concerned with how speech is produced, how speech impairment might be corrected, how hearing loss can be alleviated, and even how snoring is produced. Some acoustic engineers are concerned with improving the acoustics of cathedrals and concert halls, with reducing noise near freeways and road construction, and with reproducing music by speaker ...
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