Poise
Definition and meaning of Poise in chemistry.
Poise is a unit of dynamic viscosity in the CGS (centimeter-gram-second) system, equal to 1 gram per centimeter per second (g/(cm·s)). It measures a fluid's resistance to flow.
In more detail
The poise is named after physician and physiologist Jean Léonard Marie Poiseuille and was widely used in chemistry and physics before the SI system became standard. One poise equals 0.1 pascal-second (Pa·s), the modern SI unit of viscosity. Although the pascal-second is now preferred in formal scientific work, the poise remains common in older literature and specialized fields. The centipoise (cP), equal to 0.01 P, is especially useful for measuring the viscosity of everyday substances.
Key facts
| Symbol | P |
|---|---|
| CGS definition | 1 g/(cm·s) |
| SI equivalent | 0.1 pascal-second (Pa·s) |
| Field | Physical Chemistry |
Water at 20 degrees Celsius has a viscosity of approximately 1.0 centipoise, or 0.01 poise, making it a convenient reference point for viscosity measurements.
Frequently asked questions
How does poise relate to centipoise?
Centipoise (cP) is one-hundredth of a poise. Since water has a viscosity of about 0.01 P, it is also described as 1.0 cP, a more convenient scale for most laboratory measurements.
Why use poise if pascal-second is the SI unit?
The poise remains in use in older publications, specialized research, and some industrial contexts where historical data is referenced. Modern scientific work typically uses pascal-seconds for consistency with the SI system.