Table of Contents
CBSE Class 11 Notes Viscosity
What is Viscosity
The majority of the fluids aren’t ideal and provide some resistance to movement. This resistance to fluid motion is akin to the friction that occurs when a solid moves across a surface. It’s referred to as viscosity. When there is relative motion between liquid layers, this force exists.
In other words, we can say that, When a layer of a fluid slips or starts to slip on another layer in contact, tangential pressures are exerted between the two layers.
The directions are such that the layers’ relative motion is in opposition. Viscosity is the ability of a fluid to resist relative movement between its layers. The viscosity forces are the forces between the layers that oppose relative motion between them. As a result, viscosity can be viewed as the internal friction of a moving fluid.
In this article, we learnt about Viscosity which is defined as the resistance to the flow of a fluid is measured in this quantity. Liquids resist the relative motion of immersed objects and the movement of layers within them with different velocities. We also learned about types of viscosity, i.e. Dynamic Viscosity and Kinematic viscosity, and Newtonian and Non-Newtonian fluids. We hope you will find our piece of work informative and fun to read. Several fluids in the body are not ideal. This resistance to fluid motion is analogous to the friction created when solids move across a surface. This resistance to fluid motion is termed viscosity. This force is present when liquid layers move relative to one another.
So, let us learn more about viscosity and other related terms.
Viscosity Meaning
A fluid’s (liquid or gas) resistance to a change in shape or movement of adjacent sections relative to one another. It is the resistance to flow that is defined by “viscosity.”. Fluidity is defined as the reciprocal viscosity, which is a measure of flow ease.
Molasses, for example, has a viscosity that is higher than water. Because a fluid component that is forced to move carries along adjacent parts to some extent, viscosity can be thought of as internal friction between molecules, which prevents velocity disparities from developing within a fluid. When fluids are employed in lubrication and carried in pipelines, viscosity is crucial in determining the forces that must be overcome. It regulates liquid flow in spraying, injection moulding, and surface coating operations.
Types of Viscosity:
Kinematic and dynamic (absolute) viscosities are the two viscosity measurements used to describe fluids. These terms represent fluid flow in various ways depending on how they are measured, but they are interchangeable if the fluid density is known.
Kinematic Viscosity:
The ratio of viscous force to inertial force on a fluid is measured by kinematic viscosity. This is illustrated in the equation below, which may convert between dynamic and kinematic viscosity if the fluid density is known. Kinematic viscosity is the diffusivity of momentum, similar to mass and heat diffusivity.
v=μ/ρ
v: Kinematic Viscosity
μ: Absolute or dynamic viscosity
ρ: Density
Unit of Kinematic Viscosity: m 2/s or Stoke (St)
1 St(stokes) = 10-4 m 2/s or 1 cm 2/s
Dynamic (Absolute) Viscosity:
Internal resistance is measured by absolute viscosity (coefficient of absolute viscosity). A fluid’s dynamic (absolute) viscosity is defined as the tangential force required by moving one horizontal plane towards another at unit velocity while keeping the planes at the same distance from each other.
Viscosity in Motion Due to some shearing force, the fluid’s internal resistance to flow will be defined by its formula. This type of tangential force occurs when two horizontal planes collide. Viscosity is a crucial fluid characteristic during behavioural mechanic may have told you essential can machine conflict, the examination of liquid behaviour and fluid motion near solid barriers.
Dynamic Viscosity(η) =Shearing Stress/Shear rate
η=T /γ
η: Dynamic Viscosity
T: Shearing Stress
γ: Shear Rate
SI unit of Dynamic Viscosity: Pa s, kg/(ms) or N s/m2
Viscosity Examples in Daily Life:
Have you ever noticed that when the honey or some other thick liquid bottle is nearly empty, the love takes a long time to reach the bottle’s mouth? The intrinsic property of viscosity describes the behavior of a liquid in a flow.
Let’s take a look at some additional real-life viscosity instances.
Engine Lubricant
If you own a car, you may have been told by a mechanic that you need to change the engine oil every time you take it in for service. Engine oil serves a variety of important functions. It does, however, keep the engine running smoothly. Many moving parts in engines have the potential to rub against one another, causing friction. This friction can harm engine components and lead them to wear out more quickly. The engine would slow down substantially if friction built up, making it less efficient and more prone to break down.
Oil protects the moving engine parts so they don’t grind against each other and wear down as they move through your engine. Your engine’s oil also cleans, cools, and protects it. The viscosity of engine oil refers to how easily oil pours at a given temperature. Thin oils have a reduced thickness and maybe run more efficiently at lower temperatures than thicker oils.
Cooking Oil
When we go to the grocery store, we see a lot of different cooking oils, such as olive oil, mustard oil, avocado oil, coconut oil, and so on. They can all be described as fats that are liquid at room temperature. They are usually classified according to their nutritional content, health impacts, and the style of cooking we want to do with them. However, you can tell the difference between oils by their viscosity. It is a well-known fact that temperature significantly impacts fluid viscosity. Because disagreements in viscosity can substantially affect food texture, viscosity is a crucial element to consider when selecting a cooking oil.
Syrups
The syrup is another excellent example of viscosity. The enormous chains of carbohydrates in syrup, for example, move past each other much more slowly than the microscopic molecules of water. As constituent molecules glide past one another, their ungainly forms cause more friction. The syrup is used in cooking to describe practically any thick or sticky sweet liquid.
The numerous hydrogen bonds between the dissolved sugar’s many hydroxyls (OH) groups cause viscosity. Glucose syrup, maple syrup, corn syrup, golden syrup, cane syrup, and agave syrup are some of the syrups used in food preparation. Most of them are manufactured by reducing (boiling naturally sweet fluids such as cane, sorghum, maple sap, or agave nectar). On the other hand, Maise syrup is manufactured by converting corn starch to sugars through an enzymatic process.
Also read: Important Topic of Physics: Kirchhoff’s Laws
Also Read FAQs on Newtonian Fluids
What are Newtonian Fluids
A Newtonian fluid has a linear relationship between stress and strain rate, with the fluid’s viscosity being the ratio of stress to strain rate. A Hookean solid has a linear relationship between stress and strain: the modulus of the concrete is the ratio of stress to strain. Many materials have qualities between a Newtonian fluid and a Hookean solid. The materials are considered non-Hookean and are classified as viscoelastic if their characteristics are mostly solid-like. They are dubbed non-Newtonian, and the materials are defined as elastic viscous if they are mainly fluid-like.
What are Non-Newtonian Fluids?
As a result, a non-Newtonian fluid is both elastic and viscous at the same time. In fact, on an adequate time scale, all fluids are non-Newtonian; however, the time scale for many familiar fluids, such as air and water, is concise. Elastic effects dominate when the time scale of a flow “tf” is significantly less than the relaxation time tr of viscous stretchy material. This usually happens when the flow geometry changes abruptly. However, when “tf” is substantially bigger than “tr”, elastic effects relax enough for viscous products to take over.
Question: Give some examples of Newtonian and non-Newtonian fluids?
Answer: The examples are as follows:
Newtonian fluids: Water, air, alcohol, glycerol, thin motor etc.
Non-Newtonian fluids: Custard, Ketchup, Shampoo, Blood, paint, etc.
