SOUND 

 EXPERIMENT 80. SOUND DUE TO VIBRATION 



ATTACH a thin cork 2 inches in diameter to a brass rod 

 about 5 feet in length, and clamp the rod firmly, as shown 

 in the diagram. By means of a cork, C, close one end of a 

 glass tube about 2\ inches in diameter and 3 feet long, 

 and insert a little sand at the open end. Hold the tube 

 in a horizontal position and shake gently until the sand is 

 evenly distributed from end to end. Then slip the tube 

 over the rod and allow it to rest on short wooden blocks, 



FIG. 59. The sand is disturbed by sound. 



as shown in Figure 59, being careful that the cork on the 

 rod does not touch the sides of the tube. Grasp the ex- 

 tended end of the rod with a well resined cloth and stroke 

 it longitudinally. A loud, shrill note will be heard, and at 

 the same time the sand will be set in motion. 



Since the cork does not touch the tube, and since the tube 

 itself does not vibrate when the rod is stroked, what pro- 

 duces the motion of the sand ? What is your conclusion, 



82 



