Why are the units of poise and centipoise considered obsolete?
The correct answer and explanation is :
The units poise (P) and centipoise (cP) are considered obsolete because they are part of the CGS (centimetre-gram-second) system, which has largely been replaced by the International System of Units (SI). In modern scientific and engineering contexts, viscosity is more appropriately measured in pascal-seconds (Pa·s), the SI unit.
Detailed Explanation (Approx. 300 words):
Poise (P) and centipoise (cP) are traditional units of dynamic viscosity from the CGS system. One poise is defined as the viscosity of a fluid in which a force of one dyne per square centimeter maintains a velocity difference of one centimeter per second between two parallel layers separated by one centimeter. In practical terms, 1 poise = 0.1 Pa·s, and 1 centipoise = 0.001 Pa·s.
The shift away from poise and centipoise toward pascal-seconds (Pa·s) is part of a broader global movement to adopt the SI (Système International d’Unités), which promotes uniformity and simplifies calculations across scientific disciplines. The SI system is based on meters, kilograms, and seconds (MKS), which better align with the rest of modern physics and engineering.
Using CGS units like poise introduces unnecessary complexity and increases the risk of conversion errors in scientific communication. For instance, viscosity in SI units is often involved in fluid dynamics equations that use pressure in pascals, distances in meters, and time in seconds. Using poise requires additional conversion steps that can be confusing and error-prone.
Moreover, most international standards organizations, including ISO and ASTM, recommend the exclusive use of SI units. In academic publishing and industrial practice, SI compliance ensures consistency and comparability across different regions and sectors.
In summary, poise and centipoise are obsolete because they belong to an outdated measurement system that is incompatible with the globally adopted SI system. For clarity, precision, and consistency, viscosity should now be expressed in pascal-seconds (Pa·s).
