Question 1

What is dynamic viscosity and how does it differ from kinematic viscosity?

Accepted Answer

Dynamic viscosity (μ) measures a fluid's internal resistance to flow when subjected to shear stress, regardless of its density. Kinematic viscosity (ν) is dynamic viscosity divided by density (ν = μ/ρ). While dynamic viscosity quantifies the force needed to make a fluid flow, kinematic viscosity relates more to how quickly momentum diffuses through the fluid. Dynamic viscosity is measured in Pa·s or Poise, while kinematic viscosity is measured in m²/s or Stokes.

Question 2

Why are Poise and centipoise commonly used?

Accepted Answer

Poise (P) and centipoise (cP) are CGS units that have become industry standards in many applications. The centipoise is particularly useful because water at 20°C has a viscosity of approximately 1 cP, making it a convenient reference point. Many industries, especially petroleum and chemical processing, continue to use centipoise due to historical practices and the convenient scale it provides for common fluids.

Question 3

How do I convert between Poise and Pascal-second?

Accepted Answer

1 Poise (P) = 0.1 Pascal-second (Pa·s). Our converter handles this automatically - 1 Pa·s = 10 P. The centipoise (cP) is 1/100 of a Poise: 1 Pa·s = 1000 cP, which is also equal to 1000 mPa·s (millipascal-second).

Question 4

What are typical dynamic viscosity values for common fluids?

Accepted Answer

Water at 20°C: ~1 cP (0.001 Pa·s), SAE 30 motor oil at 20°C: ~400 cP, Honey: ~10,000 cP, Glycerin: ~1,500 cP, Air at 20°C: ~0.018 cP. Our converter helps translate these values to other units as needed for various engineering and scientific applications.

Question 5

When would I use slug/(foot·second) units?

Accepted Answer

Slug/(foot·second) is sometimes used in US engineering practices, particularly in aerospace and mechanical engineering applications where other imperial units are being used. It might be encountered in older technical literature or in specialized industries where imperial units are still preferred. 1 Pa·s = 0.0208854 slug/(ft·s), which our converter calculates automatically.

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