It is most usually encountered as the centistokes (cSt) (= 0.01 stokes). One stokes is equal to the viscosity in poise divided by the density of the fluid in g cm–3. This is the cgs unit, equivalent to square centimetre per second. Kinematic viscosity units Stokes (symbol: St) One poiseuille is 10 poise or 1000 cP, while 1 cP = 1 mPa It is sometimes referred to as the “poiseuille” (Pl). This is the SI unit of viscosity, equivalent to newton-second per square metre (N Many everyday fluids have viscosities between 0. Even in relation to high-viscosity fluids, this unit is most usually encountered as the centipoise (cP), which is 0.01 poise. It is the viscosity of a fluid in which a tangential force of 1 dyne per square centimetre maintains a difference in velocity of 1 centimetre per second between two parallel planes 1 centimetre apart. Poise (symbol: P) Named after the French physician Jean Louis Marie Poiseuille (1799– 1869), this is the CGS unit of viscosity, equivalent to dyne-second per square centimetre.

s/ft2).ĭynamic Viscosity Units Poise (symbol: P).

An alternative and equivalent unit is pound-force-seconds per square foot (lbf In American and British engineering, another common unit is pound-seconds per square foot (lb This makes the viscosity of water at 20 ☌ about 1 cP or 1 mPa However, you’ll often see viscosity expressed in terms of pascal-second (Pa The SI unit for viscosity is newton-second per square meter (N And, of course, dynamic viscosity and kinematic viscosity have different units. While the relationship is straightforward, it’s important to remember two fluids with the same dynamic viscosity values may have different densities and thus difference kinematic viscosity values. Absolute or dynamic viscosity is a measure of a fluid’s resistance to flow while kinematic viscosity is the ratio of dynamic viscosity to a fluid’s density.

Gas viscosity is not significantly affected by intermolecular attraction, but by increasing temperature, which causes more molecules to collide. As gas temperature increases, viscosity increases. The effect of temperature on viscosity is the opposite for gases. Temperature increases in a liquid decreases viscosity because it gives molecules enough energy to overcome intermolecular attraction. Temperature, however, has the greatest impact on viscosity. Sugar, for example, makes water more viscous. Adding molecules can have a significant effect. Pressure has a small effect on liquids and is often ignored. Examples include temperature, pressure, and the addition of other molecules. A fluid with a low viscosity is said to be “thin,” while a high viscosity fluid is said to be “thick.” It is easier to move through a low-viscosity fluid (like water) than a high-viscosity fluid (like honey). When we fill the same cup with water, for example, the water will drain much more quickly. This is because honey’s viscosity is relatively high when compared to other liquids. I notice that the cup drains very slowly when we pour honey into it. Consider a cup made of styrofoam with a hole at the bottom. The best way to visualize this is through an example. Just like in the case of friction between moving solids, viscosity will determine the energy required to make a fluid flow. This can also be considered to be friction between the molecules. On a molecular level, viscosity is caused by the interactions between different molecules in a fluid. Fluids with low viscosity flow easily because their molecular makeup creates little friction when they are in motion. Viscous fluids resist motion because their molecular makeup creates a lot of internal friction.

A fluid’s viscosity is a measure of its resistance to flow. It describes the internal friction of a moving fluid.

Dynamic viscosity si units