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).<ref>Template:Cite book</ref> 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 <math>\mathrm{force \times time/area}</math>, that is, <math>[\mathsf{M}^1 \mathsf{L}^{-1} \mathsf{T}^{-1}]</math>.
<math display=block>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}.</math>
The analogous unit in the International System of Units is the pascal-second (Pa⋅s):<ref>Template:Cite book</ref>
<math display=block>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}.</math>
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.<ref>Template:Cite book</ref> 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).<ref>Template:Cite book</ref>
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).<ref>"Viscosity of Liquids", in CRC Handbook of Chemistry and Physics, 91st Edition, W.M. Haynes, ed., CRC Press/Taylor and Francis, Boca Raton, Florida, 2010-2011.</ref>