What Are The Newtonian Liquids?

WHAT ARE THE NEWTONIAN LIQUIDS?
– Computer Aided Design & The 118 Elements 10/31/23, 03:42
Computer Aided Design & The 118 Elements
by Florin FODOR
WHAT ARE THE NEWTONIAN LIQUIDS?
Liquid and gas are 2 different states of matter yet they have a lot in
common. Both are fluid and both have free flow. In physics, the term
fluid refers to any material that continuously changes its shape and
form under the influence of any force or stress. The shear modulus of
fluid is zero, which means such substances cannot resist any force.
And Free Flow is a characteristic attribute of fluids that describes the
continuous and irreversible change in position of one portion of a
material relative to another when it is subjected to shear stress. But
before diving into the concept of fluid, we must have a basic
understanding of very important 3 terms. These are: Viscosity, Shear
Stress and Shear Strain.
https://americanbobcat.blog/2023/06/21/what-are-the-newtonian-liquids/ Page 1 of 8
WHAT ARE THE NEWTONIAN LIQUIDS? – Computer Aided Design & The 118 Elements 10/31/23, 03:42
VISCOSITY: is the measure of a fluid’s resistance to flow, namely to

deformation at a particular rate.
At a molecular level, viscosity is the result of 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, with other words we can say that viscosity
will determine the energy required to make a fluid flow. There are 2
main types of viscosity: dynamic and kinematic.
Dynamic viscosity (η= “eta”) (also known as absolute viscosity) gives

you information on the force needed to make the fluid flow at a certain
rate. The most commonly used unit for dynamic viscosity is the CGS
unit centipoise (cP), which is equivalent to 0.01 Poise (P). The viscosity
of distilled water at 20°C is used to define 1 cP.
The SI unit for dynamic viscosity is the Pascal-second (Pa-s), which

corresponds to the force (N) per unit area (m2) divided by the rate of
shear (s-1) a.k.a. Newton second per square meter (N·s/m2). However,
since the viscosity of most fluids is below 1 Pa-s the millipascal-
second (mPa-s) is often used instead. 1 mPa-s = 1 cP.
Kinematic viscosity (ν = “nu”) refers to how fast does the fluid flow
when a certain force is applied. The kinematic viscosity is often
measured in the CGS unit centistokes (cSt), which is equivalent to
0.01 stokes (St or cm2·s−1 = 0.0001 m2·s−1). 1St = 1P/ρ (ρ = ”rho” =

density of the fluid in g/cm3). The kinematic viscosity of water at 20
°C is about 1 cSt.
The SI unit for kinematic viscosity is square meters per second (m2/s).
However, due to the viscosity values of most common fluids, square
centimeters per second (cm2/s) is used more often. 1 cm2/s = 100 cSt.
These are the most basic units used for viscosity measurement, but
there is a large variety of units that are specific to some particular
measurement system or application. For instance, In the automotive
industry the viscosity index is used to describe the change of viscosity
with temperature.
SHEAR STRESS (τ = “tau) : is the component of stress that is parallel

to the surface and can be defined as force (N) per unit area (A), with
the force being applied externally due to various reasons. It is
commonly measured in Pascal (Pa) (1Pa= 1N/m2). In comparison the
normal stress (σ = “sigma”) (compression or tension) is perpendicular
to the surface but is also measured in Pascal.
SHEAR STRAIN: can be defined as the amount of deformation

experienced by the body in the direction in which the force is applied,
divided by the original or initial dimensions of the body. Strain can be
a result of stress itself. A shearing strain is never accompanied by a
change in volume. That means in shear strain the body gets distorted
resulting only in an alternation in its shape but not in size. Change in
shape or size need not necessarily imply strain. For example, if a body
is heated to expand, its volume changes. It acquired new size due to
expansion. However, the strain remains zero. Unless and until internal
elastic forces operate to bring the body to the original state, no strain
exists. Shear strain is unitless and dimensionless.
Sir Isaac Newton used a differential equation for the first time, to find
out the relation between these 3 terms for fluids. Among his many
well-known accomplishments, Newton discovered the basic principles
of viscosity in 1687. According to Newton’s observations, a fluid’s

viscosity is a function of shear stress and temperature, therefore he
established a mathematical relationship between the 3 terms which is
today called in his honor the Newton’s Law of Viscosity.
NEWTON’S LAW OF VISCOSITY

The Newtonian law of viscosity states that the shear stress must be
directly proportional to the velocity gradient, also called the rate of
shear strain. Mathematically the Newton’s equation is explained in fig
2 below:
According to Newton no stirring or such actions will change the

viscosity of a fluid. However, this does not always happen. You may
have noticed that if curd is beaten for a long time, its consistency
becomes thinner. However, in case of water, there is no change in the
viscosity even if it is stirred for long. Therefore it can be said that
Newton understood only half of the picture of the whole
scenario. That’s why now we divide fluids in 2 main categories:

Newtonian fluids (which obey Newton’s law of viscosity) and Non-
Newtonian fluids (which don’t behave according to Newton’s law).
NEWTONIAN FLUIDS.
A fluid is a Newtonian fluid: if its viscosity remains constant for a given
temperature and pressure, no matter the amount of shear applied (such as
mixing or a sudden application of force), hence the viscosity is simply defined
as the ratio of shear stress to shear strain rate.
Newtonian fluids are single-phase fluids made up of tiny molecules in

general (but not always). In the case of Newtonian Fluids “Viscosity of
the Newtonian fluid is solely a function of the fluid’s condition,
particularly its temperature“. The viscosity tensor is reduced to 2 real
coefficients reflecting the fluid’s resistance to continuous shear
deformation and continuous compression or expansion, respectively,
when the fluid is also isotropic (mechanical properties are the same in
all directions). It is possible for the viscosity of a Newtonian fluid to
change through factors other than externally applied force, such as
through temperature and pressure. In case of liquids, those which are
Newtonian are also incompressible, namely they exhibit a negligible
change under pressure. The defining factor of any Newtonian fluid is
that it will flow the same when a great deal of force is applied as when
it is left alone. This means that it can be mixed vigorously without
changing its viscosity.
While no real liquid or gas exactly meets the description, many

common liquids and gases, like water and air, can be considered to be
Newtonian for practical calculations under normal circumstances. The
viscosity of a Newtonian fluid, at a given temperature and pressure,
can be determined with a single measurement at any shear rate.
Newtonian fluids are mathematical models of fluids that are the
simplest and viscous.
One well known example is water, since it flows the same way
regardless of whether it is left alone or agitated vigorously. This can be
contrasted with non-Newtonian fluids, which can become thicker or
thinner when stress is applied. However, it is possible for the viscosity
of a Newtonian fluid to change if it is exposed to different
temperatures or pressures instead of external applications of force.
Many fluids become thicker as they are cooled, for example, though
they still react to shear forces without a change in viscosity. Water
retains its viscosity even after the application of external force.
The great majority of most common fluids (liquids and gases) such as
water, organic solvents, oils, air, steam, nitrogen, oxygen, hydrogen or
rare gases are Newtonian in wide temperature and pressure ranges.
WHY DO YOU NEED TO KNOW THE

DIFFERENCE BETWEEN
NEWTONIAN AND NON-
NEWTONIAN LIQUIDS?
It’s important to fully understand the properties of the fluids you’re
transferring, mixing, or pumping because viscosity plays a major role
in sizing and selecting equipment, such as the pump and sizing for
sanitary, industrial, water and wastewater, pulp & paper, and tissue
applications and many more. Understanding how a fluid reacts to
shear will help you properly size and select all the equipment it
touches.
For instance one common application for Newtonian liquids is for

Lubricants. Newtonian fluids (such as oil and its derivates) are ideal
for lubrication applications. Even though they alter viscosity as a
function of temperature, these fluids do not change viscosity as a
function of shear. A good example is motor oil. In a nutshell, it remains
fluid at lower temperatures but doesn’t get too thin at higher engine
operating temperatures. The important thing is that it does not change
viscosity when it is shared between the engine elements. This is critical
if it is to perform its function of separating parts and decreasing
friction and wear. If the viscosity tumbled as a function of shear, it
would be easily dislodged, and the metal components would destroy
each other.
June 21, 2023

MATERIALS SCIENCE
WEBSITE BUILT WITH WORDPRESS.COM.
UP ↑

What Are The Newtonian Liquids? - Computer Aided Design & The 118 Elements

Uploaded by

Copyright:

Available Formats

What Are The Newtonian Liquids? - Computer Aided Design & The 118 Elements

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

What Are The Newtonian Liquids? - Computer Aided Design & The 118 Elements

Uploaded by

Copyright:

Available Formats

– Computer Aided Design & The 118 Elements 10/31/23, 03:42

Computer Aided Design & The 118 Elements

WHAT ARE THE NEWTONIAN LIQUIDS?

VISCOSITY: is the measure of a fluid’s resistance to flow, namely to

At a molecular level, viscosity is the result of interaction between the

Dynamic viscosity (η= “eta”) (also known as absolute viscosity) gives

The SI unit for dynamic viscosity is the Pascal-second (Pa-s), which

0.01 stokes (St or cm2·s−1 = 0.0001 m2·s−1). 1St = 1P/ρ (ρ = ”rho” =

SHEAR STRESS (τ = “tau) : is the component of stress that is parallel

SHEAR STRAIN: can be defined as the amount of deformation

of viscosity in 1687. According to Newton’s observations, a fluid’s

NEWTON’S LAW OF VISCOSITY

According to Newton no stirring or such actions will change the

scenario. That’s why now we divide fluids in 2 main categories:

Newtonian fluids are single-phase fluids made up of tiny molecules in

While no real liquid or gas exactly meets the description, many

WHY DO YOU NEED TO KNOW THE

For instance one common application for Newtonian liquids is for

June 21, 2023

WEBSITE BUILT WITH WORDPRESS.COM.

You might also like