GRAVITATION. 



53 



M 



ported below its centre ; a right cone placed on its apex ; 

 an egg standing on its end ; or a stick balanced upright 

 upon the finger. 



113. Neutral Equilibrium. A 'body supported 

 171 sucli a way that, when displaced from its 

 position of equilibrium, it tends neither to return 

 to its former position nor to fall further from it, 

 is said to be in neutral or indifferent equilibrium. 

 Such a displacement neither raises nor lowers the centre 

 of gravity. Examples : A disc supported at its centre ; a 

 sphere resting on a horizontal surface ; a right cone rest- 

 ing on its side. 



(a.) In the accompanying figure M, N and represent three cones 



placed respectively 

 in these three con- 

 ditions of equili- 

 brium. The letter 

 g shows the posi- 

 tion of the centre 

 of gravity in each. 

 If a body have 

 two or more points 

 IG * 22 ' of support lying in 



the same straight line, the body will be in neutral, stable or unstable 

 equilibrium according as the centre of gravity lies in this line, is 

 directly below it or above it. 



114. Line of Direction. A vertical line drawn 

 downward from the centre of gravity is called the 

 line of direction. As we have seen, it represents the 

 direction in which the centre of gravity would move if 

 the body were unsupported. It may be considered as a 

 line connecting the centre of gravity of the given body 

 and the centre of the earth. 



115. The Base. TJxe side on ivhich a body 

 rests is called its base. If the body be supported on 



