NEUTRAL EQUILIBRIUM. 351 



pose the coefficient of .0 zero; then when 



small t is greater or less than / 

 coefficient of 0* is positive or negativ 

 former case / ///Him value of r, ai 



in a maximum value. re the cquilr 



111 -flTr ' "^ QotU ^ e if * be less 



. 



r" 

 {)ose however that c -w , then the coefficient of 6 1 



if zero; in this case the equilibrium is said to be neutral. 



now examine th- ooei t" tf 4 in the value of r; 



this Curt! 





is a negative auantit y \vs that 7^-f r-c is a 



Maximum value of a and the equililirium is really 



following problem will funiish an instru 

 example. A frame formed of i rm rods of the length 



d by smooth hinges, is hung > smooth pegs 



in the same horizontal line at a distance ' %| , the two pegs 



being in contact with rods; shew that the frame is 



.. n each angle is 90^, and determine wh 

 the equilibrium is Ata: 



Dei j)cg8 by A .v -c thr Uam in con- 



tact with A to make an angle wit I rizon, an 



beam in contact with D to make an angle 6 :*>n; 



let M he centre of grav .- system 



below Al it may be shewn that 



