PARALLEL FORCES AND CENTRE OF GRAVITY 87 



centre of gravity and point of support which must be fulfilled 

 in < .rder that an object shall be in equilibrium. It will be found 

 that the. centre of gravity is in every case below the point of 

 support when the suspended object is in equilibrium. The 

 greater the distance between the point of support and the centre 

 of gravity, the greater is the tendency to return to the position 

 of equilibrium. 



When the centre of gravity and the point of support of an 

 object are close together the equilibrium of the object is easily 

 disturbed. A good balance partly owes its sensitiveness to this 

 condition, the centre of gravity and point of support being 

 designedly brought close together. 



It has been shown that in the case of a freely suspended 

 object the centre of gravity is at its lowest point when the 

 object is in equilibrium. Let us see how this applies to a body 

 supported upon a surface below the centre of gravity. 



Equilibrium of Object resting upon a Base. EXPT. 75. 

 Procure an oblong block of wood of about the same size as this 

 book, and about an inch thick. Draw the two diagonals on one 



FIG. 38. Relation between Centre of Gravity and the Base of Support. 



of the faces ; the centre of gravity of the block will be inside the 

 block at a point below the intersection of the diagonals. Press 

 a pin partly into the block at the point where the diagonals 

 intersect, and suspend from it a small plumb-line made of a 

 short piece of thread and a bit of lead (Fig. 38). Now place 

 the block upon a board, and notice the direction of the plumb- 

 line. Tilt the board until the block topples over. When 



