Power number
# Power number

    For Newton number, see also Kissing number in the sphere packing problem.

The power number $N_p$ (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:

    $N_{\mathrm {p} }={\frac {P}{\rho n^{3}D^{5}}}$

with

* P: power
* ρ: fluid density
* n: rotational speed in revolutions per second
* D: diameter of stirrer
