Difference Between Kinematic and Dynamic Viscosity (With Table)

Kinematic and dynamic viscosity are two measures of fluid friction that are commonly used to determine fluid flow in mechanical systems. However, there is a difference between the two that can be confusing at first. This article provides an introduction to the two types of viscosity and the distinctions between them.

Kinematic vs Dynamic Viscosity

The main difference between Kinematic and Dynamic Viscosity is that Kinematic viscosity is a measure of a fluid’s ability to resist shear stress. It is defined as the reciprocal of the fluid’s speed. On the other hand, Dynamic viscosity is a measure of a fluid’s resistance to motion. It is defined as the torque required to apply a unifying force across a given area.

Kinematic viscosity is a commonly used measurement of the resistance of a fluid to flow. It is defined as the quotient of the shear stress (force per area) applied to the fluid and the resultant shear strain (rate of deformation) across a cross-sectional area. This measurement is most often used to describe the fluid resistance to motion.

Dynamic viscosity is a measure of the fluid’s ability to move around objects. It is a measurement of how difficult the fluid is to move, in comparison to a liquid with similar properties. Because water is so much easier to move than air, its viscosity is low. But if you pour water on a hot stove, the viscosity of the water drastically increases.

Comparison Table Between Kinematic and Dynamic Viscosity

Parameters of ComparisonKinematic ViscosityDynamic Viscosity
About It is defined as the quotient of the shear stress (force per area) applied to the fluid and the resultant shear strain (rate of deformation) across a cross-sectional area.It is a measurement of how difficult the fluid is to move, in comparison to a liquid with similar properties.
Measurement Kinematic viscosity is a measure of a fluid’s ability to resist shear stress.Dynamic viscosity is a measure of a fluid’s resistance to motion
Definition It is defined as the reciprocal of the fluid’s speed It is defined as the torque required to apply a unifying force across a given area.
SI unitm2 s−1m−1 s−1
Physical Unitstokes (St)Pascal-second (Pa s)

What is Kinematic Viscosity?

What is kinematic viscosity? In simple terms, it’s the viscosity of fluid without regard to the fluid’s actual viscosity. It’s measured in units of viscosity, such as centipoise (cP) or stoke (St), and is determined by the fluid’s density and velocity.

Kinematic viscosity is a measure of the resistance fluids offer when being moved. It can be thought of as a fluid’s “thickness,” or how much it resists being moved. This has a lot of applications in engineering, especially hydraulics. In fact, kinematic viscosity is sometimes referred to as “hydraulic fluid viscosity.

”Kinematic viscosity is a measure of how thick a fluid feels under pressure. It’s a way of describing the movement of particles that make up fluid and is often used when talking about liquids or gases. Because kinematic viscosity is a unitless quantity, it can be difficult to understand how it relates to viscosity. It’s often easier to think of kinematic viscosity as a measurement of how fast a fluid flows under pressure.

Kinematic viscosity, sometimes called absolute viscosity, is a measure of the viscosity of fluid without reference to the direction of the flow. It is the ratio of a fluid’s shear stress to its velocity. It is analogous to dynamic viscosity, which is a measure of a fluid’s viscosity with reference to the direction of the flow. It is the ratio of a fluid’s density to its velocity and is usually expressed in units of centimetres per second (cm/s).

What is Dynamic Viscosity?

Dynamic viscosity is the measure of a fluid’s resistance to flow. It’s a material property that can be used to distinguish between liquids and gases. The viscosity of a liquid increases as its temperature increases, whereas the viscosity of a gas decreases as its temperature increases. You can discover more about the fascinating world of viscosity in our dedicated learning section.

The viscosity of a liquid is a measure of how difficult it is to make it flow. Viscosity is a material property and is not dependent on how much of the liquid you have. The viscosity of a liquid changes depending on the temperature and the pressure that it is under. The viscosity of a liquid also changes depending on the type of liquid that it is.

Dynamic viscosity is an engineering term used to describe the viscosity of a fluid when it is under pressure. It’s the measure of a fluid’s resistance to flow, or how thick it feels. The viscosity of a fluid depends on the material it’s made from, and how much pressure it’s under. The viscosity of a fluid is normally measured in units called poises, which are equivalent to millimetres of water per second.

Main Differences Between Kinematic Viscosity and Dynamic Viscosity

  1. Kinemtic Viscosity is defined as the quotient of the shear stress (force per area) applied to the fluid and the resultant shear strain (rate of deformation) across a cross-sectional area. Whereas, dynamic viscosity It is a measurement of how difficult the fluid is to move, in comparison to a liquid with similar properties.
  2. Kinematic viscosity is a measure of a fluid’s ability to resist shear stress. On a contrary, Dynamic viscosity is a measure of a fluid’s resistance to motion.
  3. Kinematic viscosity is defined as the reciprocal of the fluid’s speed. On the other hand, dynamic viscosity is defined as the torque required to apply a unifying force across a given area.
  4. Kinematic Viscosity’s SI unit is m2 s−1. While, m−1 s−1 is the SI unit of dynamic viscosity.
  5. Kinematic Viscosity’s physical unit is stokes (St). While, Pascal-second (Pa s) is the physical unit of dynamic viscosity.

Conclusion

Viscosity is colloquially described as “liquid thickness” and can be measured using a viscosimeter. There are two types of viscosity – kinematic viscosity and dynamic viscosity. Kinematic viscosity is measured when fluid is at rest, whereas dynamic viscosity is measured when a fluid is in motion.

References

  1. https://www.sciencedirect.com/science/article/pii/S0924424708004792
  2. https://www.sciencedirect.com/science/article/pii/S0167732217356234