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Questions and Answers
What is viscosity a measure of?
What is viscosity a measure of?
All fluids have the same viscosity.
All fluids have the same viscosity.
False
What are the two types of viscosity defined in fluid mechanics?
What are the two types of viscosity defined in fluid mechanics?
Dynamic viscosity and kinematic viscosity
Glycerine, castor oil, and tar are examples of fluids with _____ viscosity.
Glycerine, castor oil, and tar are examples of fluids with _____ viscosity.
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Match the following fluids with their viscosity classification:
Match the following fluids with their viscosity classification:
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According to Newton's Law of Viscosity, what must be present for viscous flow?
According to Newton's Law of Viscosity, what must be present for viscous flow?
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A Newtonian fluid's viscosity changes with shear rate.
A Newtonian fluid's viscosity changes with shear rate.
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Name one method used to measure viscosity.
Name one method used to measure viscosity.
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What does the coefficient of viscosity represent?
What does the coefficient of viscosity represent?
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Kinematic viscosity is measured in Pa.s.
Kinematic viscosity is measured in Pa.s.
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What is the formula relating shear stress to dynamic viscosity?
What is the formula relating shear stress to dynamic viscosity?
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The unit of dynamic viscosity in SI is __________.
The unit of dynamic viscosity in SI is __________.
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Match the types of viscosity with their descriptions:
Match the types of viscosity with their descriptions:
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Which application does viscosity NOT play a role in?
Which application does viscosity NOT play a role in?
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The dynamic viscosity is expressed in kg/ms.
The dynamic viscosity is expressed in kg/ms.
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What is the SI unit of kinematic viscosity?
What is the SI unit of kinematic viscosity?
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What is the value of 1 stoke in m²/s?
What is the value of 1 stoke in m²/s?
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Viscosity of gases decreases with an increase in temperature.
Viscosity of gases decreases with an increase in temperature.
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What type of fluids are characterized by zero viscosity?
What type of fluids are characterized by zero viscosity?
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The viscosity of liquids _________ when heated.
The viscosity of liquids _________ when heated.
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Match the type of fluid with its characteristic:
Match the type of fluid with its characteristic:
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Which of the following is an example of a Newtonian fluid?
Which of the following is an example of a Newtonian fluid?
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Cohesive forces are more significant than molecular momentum for the viscosity of gases.
Cohesive forces are more significant than molecular momentum for the viscosity of gases.
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1 cSt is equal to ________ m²/s.
1 cSt is equal to ________ m²/s.
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Which of the following describes Newtonian fluids?
Which of the following describes Newtonian fluids?
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Non-Newtonian fluids include substances like honey and paints.
Non-Newtonian fluids include substances like honey and paints.
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What is the significance of the Viscosity Index (VI)?
What is the significance of the Viscosity Index (VI)?
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The device used to measure the viscosity of fluids is called a ______.
The device used to measure the viscosity of fluids is called a ______.
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Match the type of viscometer with its description:
Match the type of viscometer with its description:
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What does the 'W' in SAE viscosity grades represent?
What does the 'W' in SAE viscosity grades represent?
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SAE-15W40 refers to a monograde oil.
SAE-15W40 refers to a monograde oil.
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Write one example of a non-Newtonian fluid.
Write one example of a non-Newtonian fluid.
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Which of the following is a characteristic of hydraulic fluids?
Which of the following is a characteristic of hydraulic fluids?
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ISO Viscosity Grades include a range of viscosities from 0 to 100.
ISO Viscosity Grades include a range of viscosities from 0 to 100.
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What does the 'W' in SAE viscosity grades signify?
What does the 'W' in SAE viscosity grades signify?
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The viscosity grade of ISO VG 22 means its nominal kinematic viscosity is __________ cSt at 40°C.
The viscosity grade of ISO VG 22 means its nominal kinematic viscosity is __________ cSt at 40°C.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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What is one of the formulas for calculating shear stress?
What is one of the formulas for calculating shear stress?
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The numbers in SAE viscosity grades indicate the viscosity of an oil only when hot.
The numbers in SAE viscosity grades indicate the viscosity of an oil only when hot.
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The formula for calculating the velocity of a shaft is __________.
The formula for calculating the velocity of a shaft is __________.
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Study Notes
Applied Fluid Mechanics (Unit 2) - Viscosity of Fluids
- Viscosity is a measure of a fluid's resistance to flow (internal resistance).
- All fluids exhibit some viscosity.
- Viscosity is a property of fluids that resists the movement of one fluid layer over another.
- Fluids with high viscosity flow slowly (e.g., glycerine, castor oil, tar).
- Fluids with low viscosity flow quickly (e.g., water, kerosene, petrol).
Newton's Law of Viscosity
- Shear stress is directly proportional to the rate of shear strain (velocity gradient).
- τ = μ (du/dy)
- τ = shear stress (N/m²)
- μ = dynamic viscosity (kg/ms or Ns/m²)
- du/dy = velocity gradient (1/s)
Types of Viscosity
- Dynamic viscosity (μ): Measures the internal resistance of a fluid. Units: Pa·s, Ns/m², kg/m·s, poise.
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Kinematic viscosity (ν): Measures the ratio of dynamic viscosity to density. Units: m²/s, stokes (St), centistokes (cSt).
- ν = μ/ρ
Viscosity and Temperature
- Liquids: Viscosity decreases with increasing temperature. Cohesion forces decrease as temperature increases.
- Gases: Viscosity increases with increasing temperature. Molecular momentum transfer increases.
Viscosity Measurement
- Viscometers or rheometers are used to measure fluid viscosity.
- Various types of viscometers include rotating drum, capillary tube, falling-ball, and Saybolt Universal.
Viscosity Measurement/ Saybolt Universal Viscometer
- Saybolt equations calculate kinematic viscosity (v(cS)) based on time (t) it takes for 60 cm³ to flow through an orifice.
- v(cS) = 0.226t – 195/t, if t < 100 SUS
- v(cS) = 0.220t – 135/t, if t > 100 SUS
SAE Viscosity Grades
- SAE viscosity grades represent viscosity at different temperatures.
- The first number signifies low-temperature viscosity.
- The second number signifies high-temperature viscosity.
ISO Viscosity Grades
- ISO viscosity grades use ISO VG followed by a number.
- The number represents nominal kinematic viscosity in cSt (mm²/s) at 40°C.
Newtonian and Non-Newtonian Fluids
- Newtonian fluids: Obey Newton's law of viscosity (e.g., water, air).
- Non-Newtonian fluids: Do not obey Newton's law of viscosity (e.g., honey, paints).
Viscosity Index (VI)
- Shows how viscosity changes with temperature.
- Important for lubricating oils and hydraulic fluids.
Applications of Viscosity
- Transparent and storing facilities for fluids (pipes, tanks)
- Bitumen used for road construction
- Sewer line/pipe flow design and analysis
- Oil and gas drilling
- Maintaining machine and automobile performance
Fluid Classification
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Ideal fluid: Imaginary fluid with zero viscosity, surface tension, and incompressibility.
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Real fluid: Practical fluid with viscosity, surface tension, and compressibility.
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Newtonian fluid: Viscosity is independent of shear rate (e.g., water, air).
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Non-Newtonian fluid: Viscosity changes with shear rate (e.g., honey, paints).
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Ideal plastic fluid: A non-Newtonian fluid in which shear stress must exceed a yield point before flow begins (e.g., drilling fluid).
Characteristics of Hydraulic Fluids
- Adequate viscosity
- Lubricating ability
- Cleanliness
- Chemical stability
- Non-corrosiveness
- Resistance to bacterial growth
- Ecologically acceptable
- Low compressibility
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Description
This quiz covers the key concepts related to viscosity in fluids from the Applied Fluid Mechanics Unit 2. Understand the definitions, formulas, and types of viscosity, as well as how temperature affects fluid resistance. Test your knowledge and grasp the importance of viscosity in fluid dynamics.