Viscosity is a physical property that affects liquid behavior. Dynamic viscosity measures a fluid’s resistance to flow, while kinematic viscosity measures resistance to flow in the presence of gravity. These measures are expressed in different units and are important for real-world applications such as paint formulation and lubrication. Products subject to varying physical conditions must have specific viscosity ratios to perform properly.
The viscosity of a liquid is an important physical property that affects the behavior of the liquid as it flows. Highly viscous liquids are more resistant to strain and flow less easily, while less viscous liquids flow more easily and are less resistant to stresses. The two main ways to measure viscosity are in terms of dynamic and kinematic viscosity. These measures are related, but have different applications.
Dynamic viscosity, also called absolute viscosity, is the most commonly used measure. It measures a fluid’s resistance to flow, in other words, the fluid’s internal friction, or how easily it can deform under mechanical stress at a given temperature and pressure. The technical definition of dynamic viscosity is the ratio of shear stress to velocity gradient. When force is applied perpendicular to the surface of a liquid, it deforms laterally or shears. The ease or difficulty of this deformation is the dynamic viscosity, sometimes referred to simply as viscosity.
Kinematic viscosity, on the other hand, measures the resistance of the liquid to flow in the presence of gravity. This measure is obtained by taking the dynamic viscosity of the liquid and dividing it by the density of the liquid. The higher the viscosity of the liquid, the less easily it will flow under the force of gravity and the higher its kinematic viscosity will be.
Dynamic and kinematic viscosity are expressed in different units of measurement. The International System of Units (SI) units for dynamic viscosity are pascal-seconds. Pascals are a measure of pressure – in this case, the shear stress applied to the liquid – while seconds measure the time it takes to deform. Dynamic viscosity can also be measured in a unit called a balance, another measure that relates pressure versus time. The common unit used to measure kinematic viscosity is stokes, or centimeters squared per second, although the SI unit of meters squared per second is sometimes used.
The use of these measurements is essential for various real-world applications. For example, it is important to formulate a paint with a certain dynamic viscosity to ensure it can be mixed and applied in the correct thickness. Kinematic viscosity measurement is most often used in cases where a fluid must flow through a pipe or lubricate machinery, such as in a car engine.
Products such as motor oil that are subject to varying physical conditions must have a specific dynamic and kinematic viscosity to perform properly. The viscosity of fluids changes with temperature and pressure. For example, in cold weather, oil thickens and becomes thicker, making it less easy to flow. It is important to know both the dynamic and kinematic viscosity ratios in this situation to predict how the oil will behave at different temperatures.
Protect your devices with Threat Protection by NordVPN
