Understanding pascal-seconds to poises Conversion
The pascal-second (Pa·s) is the SI unit of dynamic viscosity, while the poise (P) is its older CGS counterpart, named after physiologist Jean Léonard Marie Poiseuille. One pascal-second equals exactly ten poise, a tidy relationship that comes from the CGS system's use of grams, centimetres, and seconds. This conversion appears whenever legacy rheology data, textbook problems, or older lubricant specifications quote viscosity in poise while modern instruments report Pa·s.
Conversion Formula
To convert pascal-seconds to poises, multiply by this factor:
Step-by-Step Example
Convert 25 pascal-seconds to poises.
How to Convert pascal-seconds to poises
Translate SI viscosity into the classic CGS poise with a factor of ten.
- Record the Pa·s value: Start with your dynamic viscosity in pascal-seconds, e.g. 25 Pa·s.
- Multiply by 10: One pascal-second equals ten poise.
- Note the CGS origin: The clean ×10 relationship reflects the gram-centimetre-second base of the poise.
- Read the result: 25 × 10 = 250 P.
pascal-seconds to poises conversion table
| pascal-seconds (Pa-s) | poises (P) |
|---|---|
| 0 | 0 |
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 4 | 40 |
| 5 | 50 |
| 6 | 60 |
| 7 | 70 |
| 8 | 80 |
| 9 | 90 |
| 10 | 100 |
| 15 | 150 |
| 20 | 200 |
| 25 | 250 |
| 30 | 300 |
| 40 | 400 |
| 50 | 500 |
| 60 | 600 |
| 70 | 700 |
| 80 | 800 |
| 90 | 900 |
| 100 | 1000 |
| 150 | 1500 |
| 200 | 2000 |
| 250 | 2500 |
| 300 | 3000 |
| 400 | 4000 |
| 500 | 5000 |
| 600 | 6000 |
| 700 | 7000 |
| 800 | 8000 |
| 900 | 9000 |
| 1000 | 10000 |
| 2000 | 20000 |
| 3000 | 30000 |
| 4000 | 40000 |
| 5000 | 50000 |
| 10000 | 100000 |
| 25000 | 250000 |
| 50000 | 500000 |
| 100000 | 1000000 |
| 250000 | 2500000 |
| 500000 | 5000000 |
| 1000000 | 10000000 |
What is the Pascal-Second?
The pascal-second is the SI derived unit of dynamic (shear) viscosity, measuring a fluid's resistance to flow. It quantifies the shear stress needed to produce a unit velocity gradient in a fluid.
Definition
One pascal-second is the viscosity of a fluid in which a shear stress of one pascal produces a velocity gradient of one reciprocal second between adjacent layers.
Expressed in SI base units, 1 Pa·s = 1 kg·m⁻¹·s⁻¹ = 1 N·s/m². It is the coherent SI unit of dynamic viscosity and is exactly equal to 10 poise (the CGS unit), so 1 Pa·s = 1000 mPa·s = 1000 centipoise.
Origin and History
Viscosity was first characterized quantitatively through the work of Newton and later Poiseuille in the nineteenth century, with the CGS poise (named for Poiseuille) long serving as the standard unit. The pascal-second entered use with the adoption of the SI, tying viscosity directly to the pascal of pressure.
Law and Notable Facts
The pascal-second is the officially sanctioned SI unit of dynamic viscosity, though the millipascal-second (equal to the once-ubiquitous centipoise) remains far more common in practice because water at 20 °C has a viscosity of almost exactly 1 mPa·s.
Real-World Examples and Conversions
- Water at 20 °C: about 0.001 Pa·s (1 mPa·s).
- Air at room temperature: about 0.0000181 Pa·s.
- Olive oil at 20 °C: roughly 0.084 Pa·s.
- Honey: commonly 2 to 10 Pa·s depending on temperature and water content.
What is the Poise?
The poise is the unit of dynamic viscosity in the centimetre-gram-second (CGS) system, measuring a fluid's resistance to shear flow. It remains common in fields such as chemistry, food science, and petroleum engineering.
Definition
One poise is the viscosity of a fluid in which a shear stress of one dyne per square centimetre produces a velocity gradient of one reciprocal second.
In SI terms, 1 poise = 0.1 Pa·s = 1 g·cm⁻¹·s⁻¹. The everyday subunit is the centipoise (cP), equal to 0.01 poise and to 1 millipascal-second, which is why water's viscosity is famously about 1 cP.
Origin and History
The poise is named after the French physician and physiologist Jean Léonard Marie Poiseuille (1797–1869), who studied the flow of liquids through narrow tubes, work later formalized as the Hagen–Poiseuille law. The unit was adopted within the CGS system in his honour.
Law and Notable Facts
The poise is not an SI unit, but it is accepted for continued use alongside SI in many industries. Its centipoise subunit is so entrenched that viscosity tables and specifications worldwide still quote values in cP even where the pascal-second is the formal standard.
Real-World Examples and Conversions
- Water at 20 °C: about 0.01 poise (1 centipoise).
- Air at room temperature: about 0.00018 poise.
- Glycerol at 20 °C: roughly 15 poise.
- 1 poise equals 0.1 Pa·s and 100 centipoise.
Frequently Asked Questions
How many poises are in one pascal-second?
Exactly 10 poise. The factor of ten comes directly from converting the SI base units to CGS units.
How do I convert pascal-seconds to poises?
Multiply the Pa·s value by 10. Thus 25 Pa·s becomes 250 P.
How do I convert poises back to pascal-seconds?
Multiply the poise value by 0.1, or equivalently divide by 10.
Who was the poise named after?
The poise honours Jean Léonard Marie Poiseuille, whose studies of blood flow led to the Hagen–Poiseuille law describing viscous flow through tubes.
Where might I still encounter viscosity in poise?
Older polymer, asphalt, and lubricant literature often uses poise or centipoise, so converting to Pa·s helps reconcile historical data with SI-based measurements.
People also convert
Complete pascal-seconds conversion table
| Unit | Result |
|---|---|
| millipascal-seconds (mPa-s) | 1000 mPa-s |
| poises (P) | 10 P |
| centipoises (cP) | 1000 cP |
| pound-force-seconds per square foot (lbf-s/ft2) | 0.02088543 lbf-s/ft2 |
| pounds per foot-second (lb/(ft-s)) | 0.671969 lb/(ft-s) |