5. How long does it take the sound of the "pin drop" to reach a person at the farther end of the building mentioned at the end of Art. 327?
6. An echo is heard after 6 seconds. How far away is the reflecting surface, the temperature being 70°F.?
7. Why are outdoor band-stands generally made with the back curving over the band?
8. A man near a forest calls to a friend. In 4 seconds the echo comes back. How far away is he from the forest?
9. Would it be possible for us ever to hear a great explosion upon the moon? Explain.
10. If a sunset gun was fired exactly at 6:00 P.M. at a fort, at what time was the report heard by a man 25 miles away, if the temperature was 10°C.?
(3) Intensity and Pitch of Sounds
Fig. 321.—Graphic representations of (a) a noise, (b) a musical sound.
328. Musical Sounds and Noises Distinguished.—The question is sometimes raised, what is the difference between a noise and a musical sound? The latter has been found to be produced by an even and regular vibration such as that of a tuning fork or of a piano string. A noise on the other hand is characterized by sudden or irregular vibrations such as those produced by a wagon bumping over a stony street. These differences may be represented graphically as in Fig. 321, (a) represents a noise, (b) a musical tone.