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.
Dynamic Viscocity
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
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.
Changes In Temperature
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.
Liquids vs. Gases
For liquids, kinematic viscosity will decrease when temperatures increase.
For gasses, it will increase when temperatures increase.
How It's Measured
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.