88 ELEMENTARY GENERAL SCIENCE CHAP. 



this happens, notice the direction of the plumb-line with 

 reference to the base. 



It will be found by this experiment that the block topples 

 over as soon as the plumb-line falls beyond the point A of the 

 base. For any object resting upon a base to be in equilibrium, 

 a vertical line drawn from the centre of gravity downward must 

 fall within the base. When this vertical line falls outside the 

 base, the body topples over. 



EXPT. 76. Repeat the preceding experiment with thick 

 blocks of wood triangular in shape, and with cylinders and 

 cones. In this way show that a body is only in equilibrium 

 when the centre of gravity is vertically above some point of 

 the supporting surface. 



It will be evident from these experiments that a body is least 

 liable to be upset when the centre of gravity is at a considerable 

 distance from all parts of the edge of the base ; for when this is 



the case the body has 

 to be tilted through a 

 large arc before the 

 centre of gravity falls 

 outside the base. 



A funnel standing 

 upon its mouth is an 

 example of a body 

 which cannot be easily 



FIG. 39. A funnel in (A) Stable Equilibrium, overturned Oil account 



of the low centre of 



gravity and its distance 

 from the edge of the 



base (Fig. 39). It is then in stable equilibrium. If the funnel is 

 stood upon the end of the neck it can easily be overturned, 

 because very little movement is required to bring the centre of 

 gravity outside the base. It is then in unstable equilibrium. 

 When the funnel lies upon the table it is in neutral equilibrium, 

 for its centre of gravity cannot then get outside the points of 

 support. 



