text: The static stability of a system is defined by 
  the initial 
  tendency to return to equilibrium 
  conditions following some disturbance from 
  equilibrium. 
  If an object is disturbed from 
  equilibrium and has the tendency to return 
  to equilibrium, positive .rtatic Jtability exists. 
  If the object has a tendency to continue in the 
  direction of disturbance, negative static stability 
  or static instability exists. An 
  intermediate 
  condition could occur where an object dis- 
  placed from equilibrium remains in equilibrium 
  in the displaced position. 
  If the object subject 
  to a disturbance has neither the tendency to 
  return nor the tendency to continue in the dis- 
  placement direction, ncutrnl Jtatic stability ex- 
  ists. These three categories of static stability 
  in figure 4.1. The ball in a 
  are illustrated 
  trough 
  the condition of positive 
  static stability. 
  If the ball is displaced from 
  equilibrium at the bottom of the trough, the 
  initial 
  tendency of the ball is to return to the 
  equilibrium condition. The ball may roll 
  back and forth through the point of equilib- 
  rium but displacement to either side creates 
  tendency to return. The ball on a 
  the initial 
  hill 
  the condition of static insta- 
  bility. Displacement from equilibrium at the 
  hilltop brings about the tendency for greater 
  displacement. The ball on a flat, level surface 
  illustrates the condition of neutral static sta- 
  The ball encounters a new equilibrium 
  bility. 
  at any point of displacement and has neither 
  stable nor unstable tendencies. 
  
  illustrates 