// Workers AI · dad joke modeWhat did the power number say to its friend? You've got the 4th power.

This article is about the dimensionless number in fluid mechanics. For the arithmetical and algebraic operation of repeated multiplication, see Exponentiation. For the maximum number of spheres touching a common sphere sometimes referred to as the Newton number, see Kissing number.

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