text: : For Newton number, see also Kissing number in the sphere packing problem.
  The power number N (also known as Newton number) is a commonly used dimensionless number relating the resistance force to the inertia force. 
  The power-number has different specifications according to the field of application. E.g., for stirrers the power number is defined as:
  with 
  *P: power
  *ρ: fluid density
  *n: rotational speed in revolutions per second 
  *D: diameter of stirrer