text: quilibrium 
  the dy- 
  namic behavior may be stable, neutral, or un- 
  stable. Chart D illustrates 
  the mode of a 
  damped oscillation where the amplitude de- 
  creases with time. The reduction of amplitude 
  time indicates there is resistance to mo- 
  with 
  tion and that energy is being dissipated. The 
  dissipation of energy-or 
  nec- 
  essary to provide positive dynamic stability. 
  If there is no damping in the system, the mode 
  of chart E is the result, an undamped oscilla- 
  tion. Without damping, the oscillation con- 
  tinues with no reduction of amplitude with 
  time. While such an oscillation indicates posi- 
  tive static stability, neutral dynamic stability 
  exists. Positive damping is necessary to elimi- 
  nate the continued oscillation. As an example, 
  an automobile with worn shock absorbers (or 
  “dampers”) 
  lacks sufficient dynamic stability 
  and the continued oscillatory motion is neither 
  pleasant nor conducive to safe operation. 
  In 
  the same sense, the aircraft must have sufficient 
  damping to, rapidly dissipate any oscillatory 
  motion which would affect the operation of 
  the aircraft. When natural aerodynamic damp- 
  ing cannot be obtained, a synthetic damping 
  must be furnished to provide the necessary 
  positive dynamic stability. 