1. Introduction
In fluid dynamics, viscosity is
a measure of a fluid’s resistance to shearing flow. It is typically
characterized as a fluid's resistance to flow and is quantified by the ratio of
the shear stress to the shear rate. The SI unit of kinematic viscosity is
square meters per second (m^2/s).
Newton's law of viscosity is an
empirical relation that states that the shear stress exerted by a fluid on a
body is proportional to the shear rate. The constant of proportionality is
known as the dynamic viscosity. The law is named after Isaac Newton, who first
formulated it in his treatise "Philosophic Naturalis Principia
Mathematica".
The law of viscosity is valid
for Newtonian fluids, which are fluids in which the shear stress is linearly
proportional to the shear rate. Non-Newtonian fluids, such as suspensions,
emulsions, and polymer solutions, do not follow Newton's law of viscosity.
In this article, we will provide
2. What is Newton's Law of Viscosity?
Newton’s law of viscosity states that the
shear stress τ (in units of force per unit area) that a fluid exerts on a body
is proportional to the rate of shear γ (volumetric strain per unit time) in
said fluid. Mathematically, the law is expressed as:
τ = μ × γ
where μ is the dynamic viscosity of the
fluid.
Dynamic viscosity is the fluid’s resistance to flow under an applied shear rate γ. The SI unit of dynamic viscosity is the pascal-second (Pa・s). Dynamic viscosity is also sometimes referred to as absolute viscosity and is related to kinematic viscosity (ν), which is a measure of the flow of a fluid under applied shear stress,
by the relationship μ = η / ρ.
that Newton’s law of viscosity is only valid for Newtonian fluids, which are fluids in which the shear stress is linearly proportional to the shear rate. Non-Newtonian fluids, such as suspensions, emulsions, and polymer solutions, do not follow Newton’s law of viscosity
μ = Dynamic viscosity
T = Shear stress = F/A
du/dy= Rate of shear deformation
how does viscosity affect
a fluid's behaviour?
Viscosity affects fluid behaviour
in several ways. Viscous fluids generally attain turbulent flow at lower
velocities than less viscous fluids, and higher velocities are needed to
separate layers of different viscosities. In addition, viscosity affects the
rate at which fluids flow. The higher the viscosity of a fluid, the slower the
flow rate.
For Newtonian fluids, the
viscosity coefficient is also a measure of the energy dissipation at a certain
shear rate. A higher viscosity means a higher energy dissipation. Viscosity
also affects the force needed to impart motion to a fluid, known as drag (also
known as friction). A higher viscosity means a higher drag. In short, viscosity
affects the flow, force and energy dissipation of a fluid, making it a crucial
parameter to consider in any situation involving fluids.
. Newton's Law of
Viscosity is highly consequential to several industries, in particular
automobile, medical, and aeronautical. For example, in the automotive industry,
this law on viscosity reveals important information about a vehicle's engine
oil, gear oil, and other fluids which helps assess their performance. In the
medical field, this law is used to measure blood viscosity which helps diagnose
diseases and evaluate the effects of treatments. Additionally, Newton's Law of
Viscosity plays an important role in aeronautics as it assists with
manipulating materials such as fuselages for efficient motion through the air.
As such, understanding Newton's Law of Viscosity is key for determining fluid behaviour
across a wide range of industrial applications.
Newton's Law of Viscosity is an important
concept that has far-reaching implications in many fields, from the automotive
to the aeronautical industry. This law helps understand the physical properties
of fluids and their behaviour in different applications and is used to measure
the amount of resistance a fluid experiences when in motion.
Understanding and using Newton's Law of
Viscosity can help one better understand the effect of fluids on motion and how
to optimize the use of these fluids for different engineering projects and
applications. While it may seem like a simple concept, understanding it can go
a long way and may even be the key to success in various fields.
