# Power number

The power number Np (also known as Newton number) is a commonly used dimensionless number relating the resistance force to the inertia force.

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

The power-number has different specifications according to the field of application. E.g., for stirrers the power number is defined as:[1]

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

with

## References

1. Seinfeld, John H (1991). Wei, J; Anderson, J L; Bischoff, K B (eds.). Advances in Chemical Engineering. Academic Press. p. 44. ISBN 978-0-08-056564-4.