# Power number

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The **power number** N_{p} (also known as Newton number) is a dimensionless number
relating the resistance force to the inertia force. In engineering, this number, along with the Reynolds number, is one of the most widely employed dimensionless numbers.

The power-number has different specifications according to the field of application. E.g., for stirrers the power number is defined as:

**Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle N_{p} = {P\over \rho n^{3} d^{5}} }**

with

- P: power
- ρ: fluid density
- n: rotational speed
- d: diameter of stirrer