Dynamic Vs Kinematic Viscosity (Difference & Definition)

Dynamic Vs Kinematic Viscosity (Difference & Definition)

Dynamic viscosity

What is viscosity?

  • Viscosity is a basic characteristic property of all liquids.
  • When a liquid flows, it’s an inner resistance to flow.
  • Viscosity is a measure of the resistance to flow or shear.
  • Viscosity may also be termed as a drag force and is a measure of the frictional properties of this fluid.
  • temperature and pressure function of Viscosity.
  • Though the viscosities of both liquids and gases vary with pressure and temperature, they affect the viscosity in another manner.
  • Within this book, we’ll deal primarily with a viscosity of fluids and its change as a function of temperature.
  • Viscosity is expressed in two distinct forms:

    • Dynamic viscosity
    • Kinematic viscosity

What is Dynamic Viscosity?

  • Rate of shear stress is directly proportional to the velocity gradient
  • Dynamic viscosity is flowed the newton 2nd Law (Second law) as per newton second law of motion. He says which relates the acceleration with the forces.
  • Due to the force exerted on the material, the deformation causes the fluid-fluid particle to move.
  • Science ‘fluid’ Kinematics viscosity, studying only motion without thinking of force.
  • This chapter presents the first primary discussion of the science of fluid force fluid dynamics and its practical and general application.
  • A clear concept of force and acceleration is necessary to understand the speed of the transmission.
    According to Newton’s law of motion (Newton’s Second Law of Motion),
  • force (force) = Mass X Acceleration
  • f = m.a  (F=Force, M= Mass, A = Acceleration)
  • It is usually the practice of using m (Mass) in the pursuit of force for a solid.
  • But the Greek letter p is used for fluid-fluid particulars.
  • Acceleration is used only for acceleration or for acceleration.
  • The actual force applied to a particular solution according to Newton’s rule – net force,
    Its product of force and acceleration is equal to – product.
  •  Thus the fluid has viscosity – viscosity. But to develop equations of motion, the equation is considered inviscid – inviscid.
  • In reality, no true view is devoid of real fluid. But other factors such as pressure force – pressure force and gravity force –
    Since the viscous effect is insignificant relative to the gravitational force, it can be ignored, and in doing so, there is no possibility of major impairment.
  • One fact should be noted that in some cases, the force of prudence may also be important.
  • For example, glycerin cannot be ignored when a fluid flows into a narrow tube or flows between two adjacent surfaces.
  •  Since airtightness is extremely low in air motion, it can be easily ignored, but the fact that air is compressible cannot be ignored.
  • Assuming that the pressure of convection is caused by gravitational force, the equation can be written as follows (Dynamic Vs. Kinematic Viscosity).
  • Actual tension force on gravity + gravitational force = volume of force x its acceleration Net pressure force on a fluid particle + net gravity force on a fluid particle = particle mass x particle acceleration.

τ = µ x du/dy

    • du/dy = constant of proportionality
    • µ = Dynamic viscosity
    • τ = Coefficient Euler’s equation of motio

Also read :What is Bulkage of Sand?

Equation of motion

(1/p) x (dp/ds) = -v x (dv/ds)

    • p = Density of fluid
    • dA = Cross-sectional area of this fluid element
    • ds = Length of this fluid element
    • dW = Weight of this fluid element
    • P = Pressure on this element at A
    • P+dP = Pressure on this element at B
    • v = velocity of This fluid element
  • Bernoulli’s equation from Real Fluid

P+(1/2).p.v.v +p.g.h = Constant

    • P = Pressure on the element at A
    • p = Density of fluid
    • v = Velosity
    • h = elvation
    • g = gravitational elevation

What is Kinematic Viscosity?

  • Kinematic viscosity: Defined as the ratio of the dynamic viscosity (mass viscosity) of a fluid
  • Mathematically,

Kinematic viscosity  ∝ = Dynamic viscosity (µ) / Density (δ)

    • ∝ = Kinematic viscosity
    • µ = Dynamic viscosity
    • δ = Density

∝ = µ / δ

  • Topics related to acceleration and types of motion, etc. are discussed.
  • An initial discussion of the equation for pressure and total force and pressure center due to the viscosity properties and the static mass.
  • It also moves due to a very small amount of learner stress on the visual.
  • Likewise, the motion is also due to the slight imbalance in the membrane pressure on the visual.


Type of Kinematic Viscosity flow:

  1. Steady and unsteady flows
  2. Uniform and non-uniform flows
  3. Laminar and turbulent flows
  4. Compressible and incompressible flows
  5. Rotational and irrotational flows
  6. One, two, and three-dimensional flows

1. Steady and unsteady flow:-

  • Steady flow: the type of flow in which the fluid properties Remains constant with time.

u,v,w=0  dv/dt=0 dv/ds =0

    • dv= change of velocity
    • dt = time
    • ds = length of flow in the direction S
  • Unsteady flow: type of flow in which the fluid properties changes with time.

dv/dt ≠ 0  dv/ds =0

    • dv= change of velocity
    • dt = time
    • ds = length of flow in the direction S


2. Uniform and non-uniform flows:

  • Uniform flows A type of flow in which velocity pressures, density, temperature, etc. At only give time does not change with respects to scope.

dv/ds = 0, dp/ds = 0

    • dv = change of velocity
    • dt = time
    • ds = length of flow in the direction S


  • Non-Uniform: velocity, pressures, density, etc. at give time change with respect to space

dv/ds ≠ 0, dp/ds =0

Non Uniform


3. Laminar and turbulent flows:

  • Laminar flow: Defined as that type of flow in which the fluid particles move along well-defined paths or streamline, and all the streamline is strength and parallel.
    • Laminar flow is also called viscous flow or stream,
    • This type of flow is only possible at slow speed and in a viscous fluid

Laminar Flow

  • Turbulent flow: in which fluid particles more irregularly and disorderly, i.e., fluid particles move in a zig-zag way. The zig-zag irregularly of fluid properties is responsible for high energy loss.



4. Compressible and Incompressible Flows:

  • Compressible flow: Type of flow in which the density of the fluid changes from point to point or in other words, the density (p) is not constant for the fluid.
  • Thus, mathematically, for compressible flow

p  ≠ Constant

  • Incompressible flow: Type of flow in which the density is constant fluid flow. Liquids are generally incompressible then gases are compressible.
  • Mathematically, for incompressible flow

p = Constant.



5. Rotational and Irrotational Flows.

  • Rotational flow: that type of flow in which the fluid particles, while flowing along stream-lines, also rotate about their own axis.
  • Irrotational Flows: Fluid particles while flowing along stream-lines, not rotate about their own axis then that type of flow is called irrotational flow.


6. One, Two, and Three-Dimensional Flow:

  • One-dimensional:
    • This is the flow in which the flow parameter such as velocity is a function of time, and one space co-ordinates only, say axis X.
    • For a steady one dimensional flow in direction, the velocity is a function of one-space and co-ordinate only.
    • The variant of velocities in additional two mutually perpendicular directions is assumed negligible.
    • Hence mathematically, for one-dimensional

flow u =f( x), v = 0 and w = 0

    • Where u, v and w are velocity components in x, y and z directions respectively.
  • Two-dimensional flow:
    • That kind of flow in which the velocity is a function of time and two rectangular space co-ordinates say x and y.
    • For a steady two-dimensional flow, the velocity is a function of two space coordinates only.
    • The variation of velocity in that third direction is negligible.
    • Thus, mathematically for two-dimensional flow

u = fi(x, y), v = f2(x, y) and w = 0.

  • Three-dimensional flow:
    • That kind of flow where the velocity is a function of time and also three mutually perpendicular directions.
    • However, to get a constant three-dimensional stream, the fluid parameters are functions of three space coordinates (x, y, and z) only.
    • Thus, mathematically, for three-dimensional flow

u = fi(x, y, z), v = f2(x, y, z) and w = f3(x, y, z).


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