When you are calculating the viscosity of a fluid without an external force, you will need to use kinematic viscosity.
If you need help with conversions, or just need to check your work, use this calculator to go from m2/s to cm2/s and more.
Kinematic viscocity is not as difficult as it seems at first glance. To learn about it in greater detail, check out our FAQ section below.
Viscosity refers to the thickness of a liquid.
Your eighth-grade science teacher may not have taught you that there are a few different types of viscosity: dynamic and kinematic.
Let's take a look at their similarities and differences.
Most often, when the average person talks about viscosity, they are referring to dynamic viscosity. This is the internal resistance of a fluid to itself.
As a liquid is moved, the different layers of the liquid stick to one another. This stickiness is what keeps a thick liquid from pouring freely.
To learn more about dynamic viscosity, visit our dynamic viscocity page.
Kinematic viscosity is the ratio of the fluid's dynamic viscosity to the fluid's density.
Whereas dynamic viscosity is usually used to talk about how difficult it is to pour a fluid when a force acts upon it, kinematic viscosity refers to the fluid's resistance when no force but gravity is acting upon it.
While kinematic viscosity does not change with pressure, it does change with temperatures.
As temperatures decrease or increase, the molecules move more slowly or more quickly.
For liquids, kinematic viscosity will decrease when temperatures increase.
For gasses, it will increase when temperatures increase.
Kinematic viscosity is often measured using a capillary tube viscometer.
This is a device that measures how long it takes a liquid of a fixed volume to flow through a small tube.
An even simpler tool is a Zahn cup. A Zahn cup is a container with a precise hole in the bottom.
Kinematic viscosity is determined by measuring how long it takes for the container to empty.
Most often, kinematic viscosity is shown by the Greek letter "nu" (v).
The density of the fluid is shown by "rho" (ρ) while the dynamic viscosity is shown by the Greek letter "mu" (μ).
The calculate kinematic viscosity, you will need to use the following formula:
To put that into layman's terms, kinematic viscosity equals dynamic viscosity divided by density.
This formula requires you to already know the precise dynamic viscosity and density of the fluid.
Kinematic viscosity is shown with a number of units.
The simplest unit is m2/s, or square meters per second. This refers to the time it takes for a liquid to flow from one point to the next.
Another common unit of kinematic viscosity is called the Stoke (St).
Converting kinematic viscocity requires knowledge of certain ratios.
The easiest method to get accurate results is by using a conversion calculator. Nonetheless, we'll review a few common conversion factors below.
The formula for determining a Stoke is as follows:
The Stoke is a rather large unit, which makes it difficult to use for subtle shifts in kinematic viscosity. Think of it like trying to measure your height in miles.
To make it more practical, the Stoke is often divided by 100 to make the centiStoke (cSt).
You can also calculate cSt with the following formula:
These formulas might seem arbitrary, but there is an important real-world reason for it. The kinematic viscosity of water at 20 degrees Celsius (about room temperature) is exactly 1 cSt.
Whkle Stokes and centiStokes are the primary units used in kinematic viscosity, but they are hardly the only units you'll come across.
In addition to m2/s, you may find any number of metric subdivisions, such as square centimeters (cm2/s), square millimeters (mm2/s), or other, smaller units.
Kinematic viscosity might seem like a heady concept, but with the right tools, it doesn't need to be intimidating.
Converting between units can be difficult, but online calculators (like this one) can help relieve much of the headache.
If you measure a fluid that is not subject to any outside forces (except for gravity), you will want to measure kinematic viscosity.
Kinematic viscosity is used when you are dealing with Newtonian fluids. These include oil, alcohol, water, gasoline, and even glycerin, for instance.
Newtonian fluids have a consistent viscosity regardless of the pressure applied to them.
Non-Newtonian fluids (example, gels and colloids) will fluctuate in viscosity with pressure.
Kinematic viscosity is often used when you are testing lubricants or oils. It is also used to determine the thickness of fluids like paint, plasma, and asphalt.
Doctors use kinematic viscosity to determine the thickness of blood in a patient. Blood viscosity can cause a number of issues, such as high blood pressure.
Most cardiovascular diseases have some correlation with blood viscosity, so kinematic viscosity can alert a doctor to a wide variety of risk factors.