154 MECHANICS 



tern. The answer should be nearly the same but there 

 will be an error due to wrong measurement. You see it 

 makes no difference what standards you use, for the real 

 size of the body remains the same. Remember the two 

 kinds of thermometers. 



c. Find the volumes of two blocks of wood by using 

 the French and the English systems. When you get 

 through you will have no doubt in your mind which 

 standards are the easier to use. Compare the two 

 volumes. How much larger is one block than the other? 



d. Find the volumes of two boxes, in the French 

 system only. Compare the two volumes. Using the 

 graduate, see how many cubic centimeters of water are 

 required to fill each box. How do these amounts com- 

 pare with the answers which you obtained by multiplica- 

 tion? 



e. Measure the diameter of a circular tin can and 

 multiply it by 3 1-7 and by 3.1416. Then measure the 

 distance around the can with a string and compare the 

 length of the string with your answer. Which is more 

 nearly correct, the answer obtained by multiplying the 

 diameter by 3 1-7 or by 3.1416? 



59. Everything has Weight. The Balance. 



Whenever we try to lift any object we feel a ' pull 

 which we must overcome if we are to move it. We call 

 this pull toward the earth the weight of the object. We 

 say that the force of gravity pulls the object and the earth 

 together. In Section 63 we shall learn more about forces. 

 The force of gravity pulls directly toward the center of the 



