36 JUNIOR GRADE SCIENCE 



for a suspended object to be 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 a suspended 

 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 equili- 

 brium. Let us see how this applies to a body supported upon a surface 

 below the centre of gravity. 



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 vase. 



A funnel standing upon its 

 mouth is an example of a body 

 ABC which cannot be easily over- 



Fio. 28. A funnel in (A) stable equilibrium, turned on account of the low 

 b?ium nStable equilibrium ' (C centre of gravity and its dis- 



tance from the edge of the base 



(Fig. 28, A}. It is then in stable equilibrium. If the funnel is stood 

 upon the end of the neck it can be easily overturned, because very 

 little movement is required to bring the centre of gravity outside the 

 base. It is thus 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. 



QUESTIONS ON CHAPTERS V. VI. AND VII. 



19. Define the mass and weight of a material body, carefully distinguishing 

 between the terms. 



Give the British and metric measures of mass. 



20. What can you learn from the direction in which a sheet of Cardboard 

 hangs when freely suspended in turn from each of a number of points near 

 the edge ? When suspended in this way what determines the position in 

 which the cardboard remains at rest ? 



21. The top of a deal table, measures 4 ft. by 2 ft. and is inch thick. 

 It is supported by legs at the corners 2| ft. long, whose cross section is a 

 square of 2-inch side. How would you find by calculation or by experiment 

 the position of the centre of gravity of the whole table ? 



