SOUND 



2 95 



VIBRATIONS OF A ROD 



through while growing from childhood to maturity. It 



is the aim of this chapter to present some definite ideas 



concerning the nature and cause of the experiences which 



we have had. We have found that we can not only 



distinguish sounds from each other, 



but that we can also ascertain the 



direction from which most sounds 



come. The ability to determine 



the direction enables us to locate 



the source or the cause of the 



sound. Every time we look for 



the cause we find some vibrating 



body or an object that has been 



vibrating. 



202. Sound Caused by Vibra- 

 tions. When the bow is drawn across one of the strings 

 of a violin, that string will emit a tone and it can be easily 

 seen that the string is moving or vibrating back and forth 

 very rapidly. The string has a hazy 

 appearance because the eye can detect 

 only about ten separate objects or mo- 

 tions per second. The violin string 

 vibrates many times ten per second and 

 so appears to have a hazy width. If a 

 piece of steel or a ruler is clamped in a 

 vice or held firmly on the edge of a desk 

 and then made to vibrate, a tone will be 

 produced. That the ruler is vibrating 

 can easily be seen. When the vibration 

 ceases no sound can be heard. The 

 prongs of a tuning fork also look hazy at the end when a 

 tone is given out. To prove that the fork is vibrating 

 when it emits a tone, touch some water with the ends of 



TUNING FORK 



The vibrating fork 

 throws the water. 



