Viscosity is often referred to as the thickness of a fluid. You can think of water (low viscosity) and honey (high viscosity). However, this definition can be confusing when we are looking at fluids with different densities.
At a molecular level, viscosity is a result the interaction between the different molecules in a fluid. This can be also understood as friction between the molecules in the fluid. Just like in the case of friction between moving solids, viscosity will determine the energy required to make a fluid flow.
Viscosity can be measured using various methods from do-it-yourself methods to viscometers that are available in the market. (Watch our webinar on the different types of viscosity!)
You can think in terms of different fluids taking different times to, for example, pour out of a cup. Water will pour out of a glass in a fraction of a second and will take the shape of the receiving container in just as short of a time. On the other hand, a high viscosity fluid like honey would take minutes to pour out and the interface between honey and air would take just as long to settle. You might have notice that I have been talking about time when trying to establish which of those two fluids is more viscous. That's what we refer to as a measurement of kinematic viscosity or how fast does a fluid flow for a given force applied to it. In this example, the applied force is gravity. (Speaking of food, what's on the viscosity menu? Read more about food viscosity!)
Back to the subject, another way to think about it is using a piston or syringe type of setup. Imagine that you have a very low viscosity fluid (water) inside a syringe. You can probably push the fluid out using your fingers. On the other hand, if you have honey inside the syringe, you better have a prety sturdy syringe and some mechanical system to help you apply enough force. You might have also noticed that in this case I have been applying and measuring force to make the fluid flow. If I fix the time I want to take for the injection (or the injection rate) and I measure the force or stress, this is what we will refer to as a measurement of dynamic viscosity.
The number of methods and types of viscometers used to measure viscosity is rather quite large and the history of viscometry goes quite back. In general we can narrow down the options by analyzing their base principles. Described above, viscosity measurements are often distinguished as either kinematic or dynamic viscosity. While relative viscosity can give you a general number, tools that can measure dynamic viscosity or aboslute viscosity have been refined and proven to provide more reliable and accurate measurements. This is because absolute viscosity is given instead of values that compare fluids to one another. Powered by VROC® technology, RheoSense viscometers provide dynamic or absolute viscosity measurements that are absolutely reliable tools for your work!
If you are interested in learning more basics about viscosity, Check out our BACK TO BASICS series on Viscosity: