Poise (unit)

poise
Unit system	Centimetre–gram–second system of units
Unit of	Dynamic viscosity
Symbol	P
Named after	Jean Léonard Marie Poiseuille
Derivation	1 P = 1 dyn⋅s/cm^2
Conversions
1 P in ...	... is equal to ...
CGS base units	1 cm^−1⋅g⋅s^−1
SI units	0.1 Pa⋅s

The poise (symbol P; /pɔɪz, pwɑːz/) is the unit of dynamic viscosity (absolute viscosity) in the centimetre–gram–second system of units (CGS).[1] 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 ${\displaystyle \mathrm {force\times time/area} }$, that is, ${\displaystyle [{\mathsf {M}}^{1}{\mathsf {L}}^{-1}{\mathsf {T}}^{-1}]}$.

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

The analogous unit in the International System of Units is the pascal-second (Pa⋅s):[2]

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

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.[3] 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).[4]

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).[5]

See also

• Poiseuille
• Viscosity

References

1. Gooch, Jan W. (2010). Encyclopedia dictionary of polymers (2nd ed.). Berlin: Springer. ISBN 978-1-4419-6246-1.
2. Reid, Robert C. (1987). The Properties of Gases and Liquids (4th ed.). McGraw-Hill.
3. Parker, Sybil P. (1988). Fluid Mechanics Source Book (1st ed.). McGraw-Hill.
4. Lide, David R. (1994). CRC Handbook of Thermophysical and Thermochemical Data (1st ed.). CRC Press.
5. "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.