What is Viscosity?
Most fluids provide some resistance to motion, which is called "viscosity." Viscosity occurs when there is relative motion between fluid layers. It precisely quantifies the resistance to flow caused by internal friction between fluid layers as they pass one another during fluid movement. It is also a measure of a fluid's thickness or resistance to items traveling through it. A fluid with a high viscosity resists motion because its strong intermolecular forces produce a lot of internal friction, preventing layers from moving past one another. A fluid with low viscosity, on the other hand, flows readily because its molecular structure causes relatively little friction when it is in motion. Gases have viscosity as well, although it is more difficult to detect in everyday situations.
Definition of Viscosity
The following is a definition of viscosity-
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A fluid's viscosity is a measure of its resistance to flow. |
The viscosity SI unit is poiseiulle (PI). Its alternative units are newton-second per square meter (N/s m2) or pascal-second (Pa s). The viscosity dimensional formula is [M1L-1T-1]. The viscosity of liquids drops fast as the temperature rises, but the viscosity of gases rises as the temperature rises. As a result, when heated, liquids flow more freely while gases flow more slowly. Furthermore, viscosity does not decrease when the number of matter changes, making it an intense feature.
Why does Water flow more quickly than Honey?
Honey has a greater viscosity than water, hence it is thicker. Honey also has more cohesion (the strength with which particles in a fluid attract one another) than water. As a result, honey will take longer to flow than water since water has less cohesion and viscosity.
A classic illustration of viscosity is water running faster than honey. When a bottle of honey is nearly empty, the small amount of honey left at the bottom must take a very long time to reach the bottle's mouth.
In layman's terms, we may simply define viscosity as "thickness." We discovered that honey is thicker than water, indicating that it is more viscous than water. Because of the stronger intermolecular interactions between the individual particles, honey is more viscous. As a result, the particles in honey are more tightly bonded than in water. Water has a viscosity of 1.0020 cps, while honey has a viscosity of 10000 cps.
Viscosity Definition Formula
Viscosity is defined as the ratio of shearing stress to velocity gradient in a fluid. The viscosity of a fluid may be calculated by dropping a sphere into it and using the following formula-
μ = Fy/ Au
Where,
μ = dynamic viscosity in N sec/m²
F = applied force in N
y = separation distance in m
A = area of each place in m²
u = speed in m/s
SI Unit of Viscosity Formula
The pascal second [Pa s] is the SI unit of viscosity and has no specific name. The International Standard of Units, despite its self-proclaimed status as a worldwide system, has had a minimal international influence on viscosity. The pascal second is less common in scientific and technical writing than it should be. The dyne second per square centimeter [dyne s/cm2] unit of viscosity is known as poise [P] after the French biologist Jean Poiseuille (1799–1869). The centipoise [cP] and millipascal second [mPa s] are equivalent because ten poise equals one pascal second [Pa s].
Types of Viscosity Definition Formula
The viscosity of a fluid is a measure of its resistance to flow. The viscosity of a fluid may be measured in two ways-
- Viscosity in Motion (Absolute Viscosity): One method is to measure the fluid's resistance to flow when a force is applied to it. This is referred to as Dynamic Viscosity.
- Viscosity in Kinematics: The alternative method is to measure the resistive flow of a fluid under gravity's weight. This fluid viscosity measurement is known as kinematic viscosity.
Many people misunderstand the two viscosity metrics and believe they are the same. In actuality, they are rather different from one another. In a few cases, kinematic viscosity is preferable to absolute or dynamic viscosity.
Importance of Viscosity Formula in Everyday Life
While viscosity may appear to be of modest consequence in everyday life, it may be quite vital in a variety of professions.
The following are some of the examples-
- Manufacturing: To function properly, manufacturing equipment requires proper lubrication. Viscose lubricants can clog and restrict pipes. Lubricants that are too thin provide insufficient protection for moving parts.
- Cooking: The viscosity of food is a significant consideration in its preparation and serving. The viscosity of cooking oils may or may not change as they heat, but many become significantly more viscous when they cool. When fats are cold, they become solid because they are relatively viscous when heated. Some viscous fluids, such as honey, provide texture to dishes by changing the "mouth feel" of the dish.
- Medicine: Viscosity is important in medicine since fluids are injected into the body intravenously. Blood viscosity is a critical issue. Blood that is excessively viscous can form lethal internal clots, whereas blood that is too thin will not clot, resulting in catastrophic blood loss and potentially death.
- Vehicle lubrication: When you put oil in your automobile or truck, keep the viscosity in mind. This is because viscosity influences friction, which in turn impacts heat. Furthermore, viscosity influences the pace of oil consumption as well as the ease with which your car will start in hot or cold weather. Some oils have a more stable viscosity, while others react to heat or cold; if your oil has a low viscosity index, it may become thinner as it heats, which might present difficulties while driving your car on a hot summer day.
Causes of Viscosity Definition
Internal friction between the molecules in a fluid causes viscosity. Consider a flowing fluid to be made up of layers that move in relation to one another. These layers scrape against each other, and the more friction there is, the slower the flow (or the more force required to achieve flow). The following are the causes of viscosity-
- Higher temperatures, on the other hand, cause gases to "thicken," and their viscosity increases with temperature. This is because molecules in gases seldom collide or interact with one another at low temperatures, but at higher temperatures, there are many more collisions. As a result, the flow resistance of the gases increases.
- Temperatureis one of the many factors that might influence a substance's viscosity. Remember that temperature is a measure of a substance's average kinetic energy per molecule. A greater average kinetic energy per molecule leads to faster-moving molecules and, as a result, reduced liquid viscosity. Warming syrup in the microwave, for example, may cause it to flow more smoothly.
- The viscosity of a fluid can also be affected by the geometry of its molecules. Rounder molecules can more readily roll past each other than molecules with branches and irregular forms. (Imagine spilling a bucket of marbles instead of a handful of jacks.
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Non-Newtonian and Newtonian Fluids
The viscosity of a fluid is affected by temperature and pressure. The viscosity of liquids increases fast as the temperature rises. The viscosity of liquid molecules rises with increasing pressure because the barrier to liquid flow increases. We call anything a Newtonian fluid if its viscosity does not vary with pressure. If the viscosity changes as a result of stress or temperature changes, we call it a non-Newtonian fluid. For example: Water is a Newtonian fluid, but toothpaste is a non-Newtonian fluid.
Viscosity Definition Formula Testing
The most basic method of measuring viscosity is to drop a sphere, such as a metal ball, through a fluid and time its fall. The greater the viscosity, the slower the sphere descends. The viscometer, on the other hand, provides a more precise measure of viscosity.
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Viscometer on a U-Tube
Glass capillary viscometers and Ostwald viscometers are other names for U-tube viscometers.
A viscometer is made up of two reservoir bulbs and a capillary tube. The capillary, a vertical segment with a precise narrow bore, is located in one arm of the U.
When in operation, the top bulb suctions the liquid, which then flows down via the capillary into the lower bulb. A known volume is indicated by two markers (one above and one below the top bulb). The amount of time it takes for the liquid to move between these markings is related to its kinematic viscosity. Most commercial units include a conversion factor. The test liquid's time to travel between two sites is measured. The kinematic viscosity is calculated by multiplying the time recorded by the viscometer factor.
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Kinematic Viscosity
The term viscosity refers to two different quantities. To distinguish it from the other amount, the quantity stated above is sometimes termed dynamic viscosity, absolute viscosity, or simple viscosity, though it is typically just called viscosity. The other variable known as kinematic viscosity (written with the Greek symbol v "nu") is the ratio of a fluid's viscosity to density.
Kinematic Viscosity = Dynamic Viscosity/Density
v = η/ρ
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