CENTER OF GRAVITY. 



51 



Fig. 23. 



' Let A represent a coach standing on a level ; B, a cart loaded with stones 

 on a slope ; C, a wagon loaded with hay on a slope ; a a a the centers of 

 gravity ; a b, line of direction ; c d, base. 



Here it is obvious that the hay-wagon must upset, because the line of di- 

 rection falls without the base ; that the coach is very secure, because the line 

 of direction falls far within the base ; and the stone-cart, though the center 

 of gravity is low down, is not very secure, because the line of direction falls 

 very near the outside of the base. 



The effect on the stability of a body occa- 

 sioned by placing its center of gravity in a very 

 low position, is shown in an amusing toy for 

 children, represented by Fig. 23. The horse, 

 with his rider, is firmly supported on his hind 

 feet, because, by means of a leaden ball attached 

 to the bent wire, the center of gravity is brought 

 below the point of support. 

 Ty, ... If a body be placed on an in- 



body slide and clined Surface, it will slide down 

 when its line of direction falls 

 within the base : but it will roll 



when roll down 

 a slope i 



Fig. 24. 



down when it falls with- 

 out the base. Thus the 

 body, e, Fig. 24, having its line of direction e a, with- 

 in the base, will slide down the inclined surface, c d; 

 but the body h a, will roll down, since its line of di- 

 rection, b a, falls without the base. 



PRACTICAL QUESTIONS ON THE CENTER OF GRAVITY. 



1. Why does a person in rising from a chair bend forward ? 



"When a person is sitting, the center of gravity is supported by the seat; 

 In an erect position, the center of gra\ity is supported by the feet; therefore, 

 before rising it is necessary to change the center of gravity, and, by bending 

 forward, we transfer it from the chair to a point over the feet. 



