CENTRE OF GRAVITY. EXAMPLES. 



41 



ward step the body must be thrown upward in a curve, 

 like a wagon mounting repeated obstructions. 



When a load is carried on the shoulder, it should be so 

 placed tliat the line of direction may pass directly through 



Fis:. 35, 



the shoulder or back down to the 

 feet, fig. 35. An unskillful person 

 will sometimes place a bag of grain 

 as shown in fig. 36. The line falling 

 outside his feet, he is compelled to 

 draw downward with great force on 

 the other end of the bag. A man who 

 carrier a heavy pole on his shoulder should see that the 

 centre is directly over his shoulder, otherwise he will be 

 compelled to bear down upon the lighter end, and thus 

 add in an equal degree to the weight upon his body. 



If an elliptical or oval body, fig. 37, rest upon its side 

 a, rolling it in either direction elevates 

 the centre, c, because it is nearest the 

 side on which the body rests. If, 

 when raised, it be suffered to fall, its 

 momentum carries it beyond the 

 point of rest, and thus it continues 

 rocking until the force is spent. The 

 course of the centre during these mo- 

 tions is shown by the curved dotted 

 line, c. If it be placed upon end, as in fig. 38, then any 

 motion toward either side brings the centre of gravity 

 nearer the touching-point, that is, 

 causes it to descend, and the body 

 consequently falls over on its side. 

 This may be easily illustrated with 

 an c^^^ which will lie at rest upon its 

 side, but falls when set on either end. 

 The rockers of chairs, cradles, 

 and cribs, are formed on the princi- 

 If so made that tlie centre of gravity 



Tiz. 38. 



pie just explained. 



