: 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