Sound 185 



and the uneven surfaces of their bodies, just as a rubber 

 ball does not bounce well in sand. So the sound does 

 not reverberate as in an empty hall. 



Application 43. Explain why a carpeted room is quieter 

 than one with a bare floor; why you shout through your 

 hands when you want to be heard at a distance. 



Inference Exercise 



Explain the following : 



261. It is harder to walk when you shuffle your feet. 



262. The air over a lamp chimney, or over a register in a furnace- 



heated house, is moving upward rapidly. 



263. The shooting of a gun sounds much louder within a room 



than it does outdoors. 



264. A drum makes a loud, clear sound when the tightened head 



is struck. 



265. The pull of the moon causes the ocean tides. 



266. Sand is sometimes put in the bottom of vases to keep them 



from falling over. 



267. It is difficult to understand clearly the words of one who is 



speaking in an almost empty hall. 



268. The ridges in a washboard help to clean the clothes that are 



rubbed over them. 



269. One kind of mechanical toy has a heavy lead wheel inside. 



When you start this to whirling, the toy runs for a long 

 time. 



270. If you raise your finger slightly after touching the surface of 



water, the water comes up with your finger. 



SECTION 30. Pitch. 



What makes the keys of a piano give different sounds? 



Why does the moving of your fingers up and down on a 

 violin string make it play different notes? 



Why is the whistle of a peanut roaster so shrill, and why 

 is the whistle of a boat so deep? 



Did you ever notice how tiresome the whistle on a 

 peanut roaster gets? Well, suppose that whenever you 



