CENTER OF MASS 



15 



piece of thread. Then tie the thread to the balance so that 

 the stone is entirely immersed in water, but does not touch 

 the sides or bottom of the vessel holding the water. Find the 

 weight of the stone in this position; is it the same as before? 

 What is the exact amount of difference? 



FIG. 6. 



FIG. 7. 



6. Remember that water is pushed out of the way by the 

 stone, and that this water exerts force in pushing up, or buoy- 

 ing up, the stone. How many grams of water, then, has the 

 stone pushed out of the way? If this water were at 4 C., 

 what would its volume be? What, then, is the volume of the 

 stone? Record your results systematically. 



EXERCISE 11 

 CENTER OF MASS 



Apparatus and Materials. Cork, cork-borer or small file (rat-tail 

 or triangular), shot, toy called a " tumbler," Mason fruit jar, pail of 

 water. ..,, 



a. In a large cork bore a hole lengthwise, at one side of the 

 center (Fig. 8) . If you have no cork-borer, you can use a small 

 file or the small blade of a penknife. Fill the hole with shot 

 packed in tightly, and hold the shot in place with wads of paper 



