poise

The unit of absolute, or dynamic, viscosity in the centimeter-gram-second system of units. Symbol, P,1 though some say Po. The poise is the most commonly encountered unit of viscosity, often as the centipoise.

Viscosity is the property of a liquid that resists flowing, sort of internal friction. Molasses, for example, has a higher viscosity than water. One poise is the viscosity of a fluid that requires a shearing force of 1 dyne to move a square centimeter area of either of two parallel layers of fluid 1 centimeter apart with a velocity of 1 centimeter per second relative to the other layer, the space between the layers being filled with the fluid. One poise = 0.1 pascal-second = 0.1 poiseuille.

This unit was defined around 1924, and named for Jean Louis Marie Poiseuille (1779–1869). Its pronunciation reflects its French origin: not like the poise in “she showed great poise,” but pwäz.

To give some idea of the magnitude of the centipoise, here are the approximate viscosities of a few common substances:

Substance Approximate Viscosity
at room temperature
in centipoises
water 1
antifreeze 15
olive oil 100
glycerin 500
motor oil 1000-2000
maple syrup 1600
honey 2000-10,000
shampoo 7000
molasses 5,000-10,000
chocolate syrup 20,000
Heinz ketchup 50,000-70,000
toothpaste 100,000
peanut butter 250,000
caulking compound 7,000,000

According to the current national standard in the United StatesĀ², the poise is not to be used. The pascal-second should be used instead.

1. P according to the International Union of Pure and Applied Physics Document U.I.P. 11 (S.U.N. 65-3).

2. IEEE/ASTM SI 10™-2002.
American National Standard for Use of the International System of Units (SI): The Modern Metric System.
New York: IEEE, 30 December 2002.

See Section 3.3.3.

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