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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:
$N\_\{p\}\; =\; \{Pover$
ho n^{3} d^{5}}
with

★ P: power

★ ρ: fluid density

★ n: rotational speed

★ d: diameter of stirrer