text: the 
  to 
  tendency of a displaced body to return 
  is defined by 
  equilibrium, dynamic stability 
  If an object is 
  the resulting motion with time. 
  disturbed from equilibrium, 
  the time history 
  of the resulting motion indicates the dynamic 
  stability of the system. 
  In general, the system 
  will demonstrate positive dynamic stability 
  if 
  the amplitude of motion decreases with 
  time. The various condirions of possible 
  dynamic behavior are illustrated by the time 
  history diagrams of figure 4.2. 
  
  While static stability  is concerned with 
  
  The nonoscillatory modes shown in figure 
  
  4.2 depict the time histories possible without 
  If the system is given an initial 
  cyclic motion. 
  disturbance and the motion simply subsides 
  without oscillation, the mode is termed “sub- 
  sidence” or “deadbeat return.” 
  Such a motion 
  indicates positive static stability by the tend- 
  ency to return to equilibrium and positive dy- 
  namic stability since the amplitude decreases 
  time. Chart B illustrates the mode of 
  with 
  “divergence” by a noncyclic increase of ampli- 
  tude with 
  tendency to con- 
  tinue in the displacement direction is evidence 
  of static instability and the increasing ampli- 
  tude is proof of dynamic instability. Chart C 
  illustrates the mode of pure neutral stability. 
  If the original disturbance creates a displace- 
  ment which remains constant thereafter, the 
  lack of tendency for motion and the constant 
  amplitude indicate neutral static and neutral 
  dynamic stability. 