Physics of Viscosity Quiz
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Questions and Answers

Which of the following statements best defines viscosity?

  • The density of a fluid.
  • The ability of a fluid to conduct electricity.
  • A measure of the resistance of a fluid to flow. (correct)
  • The temperature at which a fluid boils.

All fluids possess some viscosity.

True (A)

What are the two main types of viscosity?

Dynamic viscosity and kinematic viscosity

Glycerine and castor oil are examples of fluids with _______ viscosity.

<p>high</p> Signup and view all the answers

Which of the following is a characteristic of non-Newtonian fluids?

<p>Their viscosity changes with the applied shear rate. (B)</p> Signup and view all the answers

Match the following fluids with their viscosity characteristics:

<p>Glycerine = High viscosity Water = Low viscosity Tar = Very high viscosity Kerosene = Low viscosity</p> Signup and view all the answers

What is Newton's Law of Viscosity primarily concerned with?

<p>The relationship between shear stress and shear rate in fluids.</p> Signup and view all the answers

The two systems for measuring viscosity grades commonly used are SAE and _______ viscosity grades.

<p>ISO</p> Signup and view all the answers

What is the viscosity of a fluid measured in stokes when it is equal to 0.001 m²/s?

<p>1 stoke (B)</p> Signup and view all the answers

Viscosity of liquids increases with heating.

<p>False (B)</p> Signup and view all the answers

What type of fluid has zero viscosity?

<p>Ideal fluid</p> Signup and view all the answers

For gases, viscosity __________ with an increase in temperature.

<p>increases</p> Signup and view all the answers

Match each type of fluid with its characteristic:

<p>Ideal fluid = Zero viscosity, incompressible Real fluid = All types of fluids Newtonian fluid = Fluid whose viscosity remains constant under varying shear rates Non-Newtonian fluid = Fluid whose viscosity changes under different shear rates</p> Signup and view all the answers

Alcohol is an example of a Newtonian fluid.

<p>False (B)</p> Signup and view all the answers

What measurement unit is equivalent to 1 centistoke (cSt)?

<p>0.000001 m²/s</p> Signup and view all the answers

What is the SI unit of dynamic viscosity?

<p>Pa.s (A)</p> Signup and view all the answers

Kinematic viscosity is defined as the ratio of dynamic viscosity to the density of the fluid.

<p>True (A)</p> Signup and view all the answers

What does the variable 'μ' represent in the equation τ = μ (du/dy)?

<p>coefficient of viscosity or dynamic viscosity</p> Signup and view all the answers

The unit of kinematic viscosity in CGS is called _______.

<p>stoke</p> Signup and view all the answers

Which of the following is NOT an application of viscosity?

<p>Heat transfer in metals (C)</p> Signup and view all the answers

Match the following types of viscosity with their definitions:

<p>Dynamic viscosity = Ratio of shear stress to shear strain rate Kinematic viscosity = Ratio of dynamic viscosity to density</p> Signup and view all the answers

The coefficient of viscosity is also known as the dynamic viscosity.

<p>True (A)</p> Signup and view all the answers

The formula for dynamic viscosity is given by τ = μ (du/dy), where τ represents _______.

<p>shear stress</p> Signup and view all the answers

Which of the following fluids are classified as Newtonian fluids?

<p>Water (C)</p> Signup and view all the answers

Non-Newtonian fluids obey Newton's law of viscosity.

<p>False (B)</p> Signup and view all the answers

What is the purpose of the viscosity index (VI)?

<p>To show how the viscosity of a fluid changes with temperature.</p> Signup and view all the answers

Fluids that do not follow Newton's viscosity law are called ___.

<p>Non-Newtonian fluids</p> Signup and view all the answers

Match the following viscometers with their type:

<p>Rotating drum viscometer = Rotational measurement Capillary tube viscometer = Capillary action measurement Falling-ball viscometer = Falling ball measurement Saybolt Universal viscometer = Time-based measurement</p> Signup and view all the answers

What does the first number in SAE-15W refer to?

<p>Viscosity at low temperature (A)</p> Signup and view all the answers

Saybolt Universal Seconds (SUS) measure the viscosity of fluids.

<p>True (A)</p> Signup and view all the answers

Identify one kind of fluid that is classified as a Non-Newtonian fluid.

<p>Honey</p> Signup and view all the answers

How many ISO Viscosity grades are there for oils used in industries?

<p>20 (A)</p> Signup and view all the answers

ISO VG 22 refers to a viscosity grade of 22 cSt ± 10% at 40°C.

<p>True (A)</p> Signup and view all the answers

What does the 'W' in SAE viscosity grades signify?

<p>Winter viscosity</p> Signup and view all the answers

The viscosity of a liquid is its resistance to _____ .

<p>flow</p> Signup and view all the answers

Match the following characteristics of hydraulic fluids with their definitions:

<p>Non-corrosiveness = Does not cause damage to materials Chemical stability = Maintains properties over time Adequate viscosity = Sufficient thickness for lubrication Ecologically acceptable = Safe for the environment</p> Signup and view all the answers

What is the formula for calculating the power of the shaft?

<p>P = (2πNT) / 60 (C)</p> Signup and view all the answers

Shear stress is calculated by dividing shear force by area.

<p>True (A)</p> Signup and view all the answers

What is the significance of the first number in a SAE viscosity grade such as 15W/40?

<p>It indicates the viscosity at cold temperatures.</p> Signup and view all the answers

Flashcards

What is viscosity?

Viscosity is a measure of a fluid's resistance to flow. It reflects how easily fluid layers slide past each other. The higher the viscosity, the 'thicker' or more resistant the fluid is to flow.

What is Newton's Law of Viscosity?

Newton's Law of Viscosity states that the shear stress in a fluid is directly proportional to the rate of strain. In simpler terms, the force needed to move one fluid layer relative to another is directly related to how quickly they are moving apart.

What is dynamic viscosity?

Dynamic viscosity (also known as absolute viscosity) measures the fluid's resistance to shear stress. It represents the internal friction within the fluid, quantifying its 'thickness'.

What is kinematic viscosity?

Kinematic viscosity relates a fluid's dynamic viscosity to its density. It tells how easily a fluid moves under the influence of gravity, essentially how quickly it flows.

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What are Newtonian fluids?

Newtonian fluids obey Newton's law of viscosity. Their shear stress is directly proportional to the shear rate. This means that their viscosity remains constant, regardless of the flow rate.

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What are non-Newtonian fluids?

Non-Newtonian fluids don't follow Newton's law of viscosity. Their viscosity changes depending on the flow rate. They can behave differently based on how much force is applied.

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How does temperature affect viscosity?

A fluid's viscosity generally changes with temperature. For most liquids, viscosity decreases as temperature increases. It's harder to flow when cold, but easier when warmer.

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How is viscosity measured?

Viscosity measurement techniques include viscometers, which determine a fluid's resistance to flow. There are different viscometer types based on the fluid's properties and the desired data.

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Viscosity

A measure of fluid resistance to flow caused by internal friction between fluid layers.

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Shear Stress

The force exerted by a fluid layer on an adjacent layer due to relative motion.

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Velocity Gradient

The rate at which the velocity of a fluid changes across a distance.

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Newton's Law of Viscosity

The relationship between shear stress and velocity gradient. It states that shear stress is directly proportional to the velocity gradient.

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Coefficient of Viscosity (Dynamic Viscosity)

The constant of proportionality in Newton's Law of Viscosity. It represents the fluid's internal resistance to flow.

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Kinematic Viscosity

The ratio of dynamic viscosity to density. It measures the fluid's resistance to flow under gravity.

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Poise

The unit of dynamic viscosity. It is equivalent to 1 Pascal-second (Pa.s) or 1 kg/ms.

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Stoke

The unit of kinematic viscosity. It is equivalent to 1 square meter per second (m²/s).

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Newtonian Fluids

Fluids that follow Newton's law of viscosity, where the shear stress is directly proportional to the shear rate. Examples include air and water.

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Non-Newtonian Fluids

Fluids that do not follow Newton's law of viscosity. Their viscosity changes with shear rate. Examples include honey, paints, and ketchup.

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Viscosity Index (VI)

A measure of how much a fluid's viscosity changes with temperature. A higher viscosity index indicates less change in viscosity with temperature changes.

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Viscometers or Rheometers

Devices used to measure the viscosity of fluids. Different types exist based on the measurement principle.

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Saybolt Universal Viscometer

A type of viscometer that measures the time it takes for a specific volume of fluid to flow through a calibrated orifice.

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SAE Viscosity Grades

A system used to classify the viscosity of engine oils and automobile lubricants based on their viscosity at different temperatures.

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Monograde Oil

A single viscosity grade for engine oils, typically used in a specific temperature range.

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Multigrade Oil

A blend of oils with different viscosity grades, providing optimal performance across a wider temperature range.

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1 cSt

A unit of measurement for kinematic viscosity, representing 10^-6 square meters per second, or 0.000001 square meters per second.

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Viscosity Variation with Temperature

How viscosity changes with temperature.

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Liquids and Viscosity

Fluids whose viscosity decreases when heated. This is due to the weakening of cohesive forces between molecules at higher temperatures.

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Gases and Viscosity

Fluids whose viscosity increases when heated. This is because the molecular momentum, which causes friction, increases with temperature.

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Ideal Fluid

A theoretical fluid with zero viscosity, surface tension, and incompressibility.

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Real Fluid

A fluid that exists in the real world, with viscosity, surface tension, and compressibility.

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ISO Viscosity Grades

A standard classification system using numbers to categorize oil viscosity at 40°C. The higher the number, the higher the viscosity.

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Viscosity Grade

The viscosity of a fluid at a specific temperature. Higher numbers indicate a thicker fluid at that temperature.

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Adequate Viscosity

The minimum amount of viscosity needed for a hydraulic fluid to properly lubricate and prevent wear in a system.

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Lubricating Capability

The ability of a fluid to reduce friction between moving parts, preventing wear and tear.

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Cleanliness

The measure of impurities in a fluid. It affects the fluid's performance and lifespan.

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Chemical Stability

The ability of a fluid to resist changes in its chemical composition over time. This ensures the fluid remains effective.

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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, or its internal resistance to flow.
  • It is a fluid property that resists the movement of one fluid layer over another.
  • All fluids have some resistance to flow, therefore all exhibit viscosity.
  • Viscosity is a crucial property in numerous applications, including:
    • Transparent and storage facilities for fluids (e.g., pipes, tanks)
    • Bitumen use in road construction
    • Design and analysis of sewer lines or other pipe flows
    • Oil and gas drilling
    • Maintaining machine and automobile performance by determining lubricant thickness.

Viscosity of Fluids: Types

  • Dynamic viscosity (μ): Represents the internal resistance to flow of a fluid.
  • Kinematic viscosity (ν): Defined as the ratio of dynamic viscosity to the fluid's density.

Viscosity: Measurement

  • Viscometers or Rheometers measure fluid viscosity.
  • Common types of viscometers include:
    • Rotating drum viscometer
    • Capillary tube viscometer
    • Falling-ball viscometer
    • Saybolt Universal viscometer

Viscosity: Variations

  • With temperature:
    • Liquids: Viscosity decreases as temperature increases.
    • Gases: Viscosity increases as temperature increases.
  • Generally independent of pressure (for incompressible fluids).

Viscosity: Newtonian vs. Non-Newtonian Fluids

  • Newtonian fluids: Fluids that obey Newton's Law of Viscosity (shear stress is directly proportional to the rate of shear strain). Examples include water, air and kerosene.
  • Non-Newtonian fluids: Fluids that do not obey Newton's Law of Viscosity. Examples include honey, paints, and some drilling fluids.

Viscosity Index (VI)

  • Viscosity index (VI) shows how viscosity changes with temperature.
  • Important for lubricating oils and hydraulic fluids used in equipment operating at extreme temperatures.

SAE Viscosity Grades

  • SAE viscosity grades are used to categorize engine oils and automobile lubricants.
  • The first number of an SAE viscosity grade (e.g., SAE 15W40) refers to viscosity at low temperatures, while the second number (40) refers to viscosity at 100°C.

ISO Viscosity Grades

  • ISO viscosity grades are used for industrial oils.
  • The designation is ISO VG (e.g., ISO VG 22), followed by a number representing the nominal kinematic viscosity in cSt (mm²/s) at 40°C.

Characteristics of Hydraulic Fluids

  • Adequate viscosity: Necessary for proper functioning.
  • Lubricating capability: The fluid must lubricate components.
  • Cleanliness: Crucial for preventing contamination.
  • Chemical stability: The fluid must maintain its properties over time.
  • Non-corrosiveness: The fluid shouldn't corrode equipment.
  • Ability to resist bacterial growth: Necessary for preventing biofouling.
  • Ecologically acceptable: Environmentally friendly materials.
  • Low compressibility: Essential for maintaining pressure in hydraulic systems

Newton's Law of Viscosity

  • A force is required to move a fluid layer atop another fluid layer.
  • Shear stress is proportionally related to the velocity gradient or shear strain.
  • Velocity (u) = (πDN)/60
  • Shear stress = Shear Force/Area
  • Area = πdL
  • Torque (T) = radius of the shaft * Shear force
  • Power (P) = (2πNT)/60

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Applied Fluid Mechanics (Unit 2) Viscosity of Fluids PDF

Description

Test your understanding of viscosity with this quiz focused on fluid dynamics. Explore key concepts such as Newton's Law of Viscosity, types of fluids, and various measurement units. Perfect for students studying physics or engineering.

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