# Difference Between Kinematic and Dynamic Viscosity

Edited by Diffzy | Updated on: August 09, 2022

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## Introduction

We refer to this resistance to motion that most fluids provide as "viscosity." When there is relative motion between the fluid's layers, viscosity develops. More specifically, it measures flow resistance brought on by internal friction between fluid layers that occur when they pass one another during fluid flow. The term "viscosity" can also be used to describe a fluid's thickness or resistance to being penetrated by foreign objects. Strong intermolecular forces provide a lot of internal friction in a fluid with a high viscosity, which makes it difficult for layers to move past one another. A fluid with low viscosity, on the other hand, flows smoothly because its molecular structure causes less friction when it is in motion. Viscosity is also present in gases, but it is less obvious in everyday situations.

Viscosity quantifies the obstruction to a liquid's flow that results from internal frictions between fluid layers. A liquid's viscosity reduces as its temperature rises. A molecule's kinetic energy increases with increasing temperature, which causes molecules to slide past one another between layers. It is possible to think of viscosity as the friction that occurs between fluid molecules. The assessment of a fluid's resistance to a progressive deformation caused by tensile or shear stress is known as viscosity. When the liquid layers are moving relative to one another, there is viscosity. The majority of this liquid has some motion resistance and is not ideal. This friction caused by a fluid moving against it is comparable to internal friction, which is comparable to friction caused by a solid moving against a surface.

In general, a fluid's state—including its temperature, pressure, and rate of deformation—determines its viscosity. In some circumstances, the dependence on some of these traits is minimal. For instance, the rate of deformation does not affect the viscosity of a Newtonian fluid. Superfluids are the only fluids that exhibit zero viscosity, or no resistance to shear stress; in all other fluids, positive viscosity is required by the second law of thermodynamics. Ideal or inviscid fluids are those with no viscosity. Let's say someone had two bowls, one of which is filled with water and the other with honey. Honey would require more time to shape the bowl than water would. This occurs as a result of the two fluids' differing viscosities. The characteristic of liquids that stops them from spreading is their viscosity. The characteristic of liquids known as viscosity prevents relative motion between its many layers. Viscous force is the name for the force caused by viscosity. Internal friction is another name for this force, which acts between liquid layers. Fluid in motion possesses a variety of qualities and contains a variety of energies. Because not all liquids are ideal liquids and because they exert some resistance to motion, the moving fluid has numerous characteristics that prohibit it from being an ideal liquid. This resistance to motion in liquids is known as viscosity, and it can be thought of as internal friction similar to that created by motion on the surface of solids. This force is present whenever there is relative motion between the fluid surfaces.

Viscosity is the characteristic of a liquid that causes an opposing force (internal friction) to act between various layers of the liquid whenever there is a relative motion between these layers. Consider a fluid that is travelling perpendicularly to it in the horizontal plane. One might imagine that the fluid is made up of numerous layers. The layer that is in touch with the horizontal plane will have a velocity of roughly zero if the fluid flow is acute. However, the layer's flow velocity will grow as the layer's separation from the horizontal plane widens.

### The Uses of Viscosity

Everyday life has made use of knowledge of the viscosity of various liquids and gases. Following are some examples of how this expertise has been applied:

• The molecular weights of organic liquids are determined using their coefficient of viscosity.
• Choosing the ideal lubricant for each machine is made possible by understanding the coefficient of viscosity and how it changes with temperature. In light machinery, thin oils with low viscosity are used. Oils with high viscosity are used in large machinery. The most crucial aspect of lubricating oils in lubrication is viscosity, which is commonly disregarded in greases yet is quite crucial. Viscosity is the scientific term for resistance to motion. Because it moves swiftly, water has a low viscosity, whereas honey has a high viscosity.
• A few medications' viscosities have been lowered to facilitate application, such as the various solutions used to remove moles. Drug companies sell medications that are highly viscous but still drinkable, like cough syrup, to coat the throat.
• The viscosity of paints, varnishes, and other household products is carefully regulated so that they can be applied with a brush roller smoothly and consistently.
• When preparing and presenting food, viscosity is crucial. Cooking oils may or may not change in viscosity when they heat, although many do so significantly more so when they cool. Due to their nasty nature when heated, fats solidify when they are cold.
• A suitable lubricant must be used on manufacturing equipment for it to operate correctly. Pipes can become blocked by lubricants that are too viscous. Lubricants that are too thin don't protect moving parts well enough.
• One of the key factors that affect the success of the coating procedure is coating viscosity. The viscosity of the coating is a crucial characteristic to control since it commonly affects the uniformity and reproducibility of the coating procedure.

## Kinematic Viscosity vs. Dynamic Viscosity

Many physics phrases include crucial information yet are difficult to understand because of minor discrepancies. Every phrase in physics is crucial because it clarifies the logical events that take place on Earth, just as the idea of gravity clarifies the everyday events taking place all around us. The primary distinction between kinematic and dynamic viscosity is that, when inertia and viscous force are both dominant, dynamic viscosity to density must be used (it is influenced and dependent on dynamic viscosity as well), and it represents both forces and is measured in units of m2/s. In contrast, dynamic viscosity is used when viscous force alone is dominant and shear stress to shear strain ratio is required.

## Difference Between Kinematic Viscosity and Dynamic Viscosity in Tabular Form

 Parameters of Comparison Kinematic Viscosity Dynamic Viscosity Definition A study that doesn't take into account the sources of motion while describing how points, bodies (objects), and systems of bodies (groups of objects) move An examination of forces, torque, and how they affect motion. Utilized as a research subject Robotics, mechanical engineering, applied mathematics, biomechanics, and astrophysics. Engineering with a focus on mechanical systems. Properties Only interested in the characteristics of motion, such as acceleration, displacement, and velocity. Analyzing the forces acting on any moving body and their analysis. Also known as Spreading of momentum Total viscosity Ratio Viscosity to density dynamic The ratio of shear strain to shear stress.

## What is Kinematic Viscosity?

Kinematic viscosity is one way to gauge a fluid's internal resistance when subjected to a planet's gravitational pull. The capillary inside a calibrated viscometer is kept at a specified temperature to achieve the measurement goal. A certain distance must be covered in a known length of time with a known volume of fluid. Kinematic viscosity is one way to gauge a fluid's internal resistance when subjected to a planet's gravitational pull. The capillary inside a calibrated viscometer is kept at a specified temperature to achieve the measurement goal. To determine the kinematic viscosity under the given circumstances, a fixed volume of fluid must traverse a known distance in a fixed period. Only under certain circumstances, such as temperature, is the result of this test valid.

Both inertia and viscous force are represented using the Kinematic Viscosity. The representational symbol for kinematic viscosity is "v." Kinematic viscosity is obtained by dividing the dynamic viscosity/density by the ratio, which is equal in this case. Kinematic viscosity is reliant on fluid density in terms of density dependency. Kinematic viscosity is frequently referred to as diffusivity of momentum in the context of kinematics. When both inertia and viscosity forces are prominent, kinematic viscosity is utilized. Kinematic viscosity is often expressed in terms of m2/s.

The type of viscosity known as kinematic viscosity is determined by dividing the fluid mass density by the dynamic fluid, absolute fluid viscosity, or viscosity. It is occasionally referred to as momentum diffusivity. Kinematic viscosity is measured in terms of time and fluid surface area. As a result, kinematic viscosity is the assessment of a fluid's inherent resistance to flow when only gravity is acting as an external force. This is a force-independent quantity that measures the dynamic viscosity to its density. By dividing a fluid's absolute viscosity by its mass density, the kinematic viscosity of the fluid may be calculated.

## What is Dynamic Viscosity?

The resistance that exists when one fluid layer crosses over another is known as dynamic viscosity. It is directly influenced by a fluid's density. The density and thickness of the fluid increase as the viscosity of the fluid increases. The viscosity is impacted by temperature changes as well. The viscosity typically decreases abruptly as the temperature rises. The resistance that exists when one fluid layer crosses over another is known as dynamic viscosity. It is directly influenced by a fluid's density. The density and thickness of the fluid increase as the viscosity of the fluid increases. The viscosity is impacted by temperature changes as well. The viscosity typically decreases abruptly as the temperature rises. As the temperature rises, the other temperature that affects dynamic viscosity also tends to become gaseous.

Adaptive Viscosity The fluid's internal flow resistance will be defined by a formula due to some shearing force. When two horizontal planes move together, a tangential force of this kind is created. When analyzing liquid behaviour and fluid motion near solid barriers, viscosity plays a key role as a fluid characteristic. Therefore, the force required by a fluid to overcome its internal molecular friction for the fluid to flow is known as dynamic viscosity. Therefore, dynamic viscosity can be defined as the tangential force per unit area needed to move a fluid in one horizontal plane relative to another plane at a unit velocity while maintaining a unit distance between the fluid's molecules.

Dynamic viscosity is used to depict the fluid's vicious force. To illustrate dynamic viscosity, the symbol "is employed. Shear stress to shear strain ratio is the unit used to measure dynamic viscosity. This indicates that determining the dynamic viscosity is necessary to calculate the kinematic viscosity. It is independent of the dynamic viscosity scenario. Another name for the dynamic viscosity is absolute viscosity. Dynamic viscosity is employed when the viscosity force alone is dominating. Dynamic viscosity is measured in Ns/m2.

## Difference Between Kinematic Viscosity and Dynamic Viscosity In Points

• They each stand for something different. Dynamic viscosity is used to express the fluid's viscous force rather than kinematic viscosity, which is used to represent both inertia and viscous force.
• Both of them, as previously indicated, stand for distinct things, and as a result, they are symbolized by various symbols. Kinematic viscosity is represented by the symbol "v," but dynamic viscosity is represented by the sign "."
• As opposed to dynamic viscosity, which is measured as the ratio of shear stress to shear strain, kinematic viscosity is measured as the ratio of dynamic viscosity to density. This indicates that to calculate the kinematic viscosity, dynamic viscosity is a must.
• They are both referred to or recognized by other names as well. Kinematic viscosity is also referred to as momentum diffusivity. Another name for the dynamic viscosity is absolute viscosity.
• Both of these are applied to kinematic viscosity in various contexts. It is utilized when both inertia and viscosity force is dominant, whereas dynamic viscosity is used when viscosity force alone is dominating.

## Conclusion

When examining the movement of liquids close to solid limits and their behaviours’ viscosity is a key fluid attribute to consider. A fluid's viscosity is a measurement of its resistance to progressive deformation brought on by tensile or shear stress. We already know that a fluid's shear resistance results from the friction between its molecules. When fluid layers try to move past one another, it occurs. As a result, we can define viscosity as a fluid's flow resistance. These terms, which are crucial to understanding much of the logic and activity occurring around us, are briefly explained. They gauge the pressures and impacts of one thing on nearby objects.

While certain terms are used frequently and others are very seldom, all of them are nonetheless significant. These phrases are used to describe how fluids flow in the environment under various temperature settings. These are crucial for research and invention, so it's crucial to comprehend the differences and eliminate any ambiguity.

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"Difference Between Kinematic and Dynamic Viscosity." Diffzy.com, 2023. Thu. 23 Mar. 2023. <https://www.diffzy.com/article/difference-between-kinematic-and-dynamic-viscosity-816>.

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