What unit is used for viscosity in the drilling mud example?

What unit is used for viscosity in the drilling mud example?

• A. cp
• B. Pa s
• C. N s/m^2
• D. S/m

Answer: (B)

Viscosity is a measure of how much a fluid resists flow, defined as the ratio of shear stress to shear rate. The SI unit for dynamic viscosity is the pascal-second, written as Pa·s. This comes from shear stress having units of newtons per square meter, and shear rate having units of per second; dividing gives newton-seconds per square meter, which is the same as Pa·s. In the drilling mud example, using Pa·s expresses that resistance to flow in standard SI terms. You might also see centipoise (cP) in drilling-fluid practice, and note that 1 Pa·s equals 1000 cP, but the SI unit shown here is Pa·s. The option S/m is for electrical conductivity, not viscosity, so it doesn’t fit.

Viscosity is a measure of how much a fluid resists flow, defined as the ratio of shear stress to shear rate. The SI unit for dynamic viscosity is the pascal-second, written as Pa·s. This comes from shear stress having units of newtons per square meter, and shear rate having units of per second; dividing gives newton-seconds per square meter, which is the same as Pa·s. In the drilling mud example, using Pa·s expresses that resistance to flow in standard SI terms. You might also see centipoise (cP) in drilling-fluid practice, and note that 1 Pa·s equals 1000 cP, but the SI unit shown here is Pa·s. The option S/m is for electrical conductivity, not viscosity, so it doesn’t fit.