Posted by **Jack** on Wednesday, January 4, 2012 at 3:56pm.

Determine the units of viscosity,m, in the following equation:

t=m(du/dy), where t is a shear stress, u a velocity, and y is a distance in (a) the Engineering English system, and (b) the SI system.

- Thermodynamics -
**Steve**, Wednesday, January 4, 2012 at 4:48pm
stress is force/area = kg-m/s^2m^2 = kg/ms^2

I'll use v distinguish viscosity from mass

kg/ms^2 = v * (m/s / m) = v/s

v = kg/ms or kilograms per meter-second

this can be verified at wikipedia under the viscosity article.

looks like t = kg * (m/s / s) = kg m/s^2 = Newtons

- Thermodynamics -
**drwls**, Wednesday, January 4, 2012 at 8:15pm
Steve is correct.

In my generation, viscosity was usually quoted in Handbooks in units of g/(cm*s), called the poise, or 1% of that, called the centipoise.

English units of viscosity were seldom used. I seem to recall some English units called Saybolt slugs. I have never heard a better argument for the metric system.

- Thermodynamics -
**drwls**, Wednesday, January 4, 2012 at 8:18pm
This may help:

http://www.hydramotion.com/pdf/Website_Viscosity_Units_V2.pdf

- Thermodynamics -
**drwls**, Thursday, January 5, 2012 at 4:54am
A sensible unit of viscosity in the English engineering system would be slugs per foot-second.

See

http://www.convertworld.com/en/dynamic-viscosity/Slug+per+foot+second.html

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