Poise (unit)

Template:Short description Template:Infobox unit The poise (symbol P; Template:IPAc-en) is the unit of dynamic viscosity (absolute viscosity) in the centimetre–gram–second system of units (CGS). It is named after Jean Léonard Marie Poiseuille (see Hagen–Poiseuille equation). The centipoise (1 cP = 0.01 P) is more commonly used than the poise itself.

Dynamic viscosity has dimensions of $\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{c}\mathrm{e}\mathrm{\times }\mathrm{t}\mathrm{i}\mathrm{m}\mathrm{e}/\mathrm{a}\mathrm{r}\mathrm{e}\mathrm{a}$, that is, $[{\mathsf{M}}^1{\mathsf{L}}^{-1}{\mathsf{T}}^{-1}]$.

$$1\text{P}=0.1{\text{m}}^{-1}\cdot \text{kg}\cdot {\text{s}}^{-1}=1{\text{cm}}^{-1}\cdot \text{g}\cdot {\text{s}}^{-1}=1\text{dyn}\cdot \text{s}\cdot {\text{cm}}^{-2}.$$

The analogous unit in the International System of Units is the pascal-second (Pa⋅s):

$$1\text{Pa}\cdot \text{s}=1\text{N}\cdot \text{s}\cdot {\text{m}}^{-2}=1{\text{m}}^{-1}\cdot \text{kg}\cdot {\text{s}}^{-1}=10\text{P}.$$

The poise is often used with the metric prefix centi- because the viscosity of water at 20 °C (standard conditions for temperature and pressure) is almost exactly 1 centipoise. A centipoise is one hundredth of a poise, or one millipascal-second (mPa⋅s) in SI units (1 cP = 10⁻³ Pa⋅s = 1 mPa⋅s).

The CGS symbol for the centipoise is cP. The abbreviations cps, cp, and cPs are sometimes seen.

Liquid water has a viscosity of 0.00890 P at 25 °C at a pressure of 1 atmosphere (0.00890 P = 0.890 cP = 0.890 mPa⋅s).

See also

• Poiseuille (unit)
• Viscosity