Common Fluid Properties

Define the terms in relation to fluid mechanics such as density, specific gravity, viscosity and vapor pressure.
Mass Density (\(\rho\)) is defined as the mass of substance per unit volume.
\[\rho = \frac{m}{V}\]
Specific gravity (s) of a fluid is the dimensionless number. \[s = \frac{\rho_{\mathrm{\ fluid}}}{\rho_{\mathrm{\ standard\ fluid}}}\] Specific Weight (\(\gamma\)) is defined as the weight per unit volume.
\[\gamma = \rho g \ \mathrm{or}\ \rho = \frac{\gamma}{g}\] Specific volume (v) is the volume occupied by a unit mass of fluid. \[\mathrm{v} = \frac{1}{\rho}\] Viscosity (\(\mu\)) of a fluid measures its resistance to flow under an applied shear stress. Representative units for viscosity are Pa.s (also known as poise designated by P). The centipoise (cP), one hundredth of a poise, is also a convenient unit, since the viscosity of water at room temperature is approximately 1 centipoise.
Kinematic viscosity (\(\nu\)) is the ratio of the viscosity to the density. \[\nu = \frac{\mu}{\rho}\]
Vapor Pressure: The pressure at which a liquid will boil is called its vapor pressure.
Solved Examples
Solved Example:
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Fluid is a substance that: (TANGEDCO AE EC 2018)
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Practical fluids:
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Density of water is maximum at:
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Poise is the unit of: (SSC JE ME Paper 4 Jan 2018 Morning)
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Choose the correct relationship:
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Choose the wrong statement:
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Kinematic viscosity is equal to: (UPSSSC JE Mech 2015 Paper 2)
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Viscosity of water in comparison to mercury is: (ISRO Scientist Mechanical 2013)
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Surface tension has the units of: (MPSC AMVI Official Paper 1: Set A/2017)
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Property of a fluid by which molecules of different kinds of fluids are attracted to each other is called:
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Specific weight of water in S.I. units is equal to:
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Which of the following is dimensionless? (NPCIL SA/ST ME GJ Nov 2019 Shift I)
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The tendency of a liquid surface to contract is due to the following property:
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A fluid in equilibrium can't sustain: (ISRO Scientist Civil 2015)
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Surface tension:
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The property of fluid by virtue of which it offers resistance to shear is called: (ISRO VSSC Technical Asst. Mechanical April 2012)
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Kinematic viscosity is dependent upon:
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Surface energy per unit area of a surface is numerically equal to:
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Choose the wrong statement:
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Surface energy per unit area of a surface is numerically equal to:
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If 850 kg liquid occupies volume of one cubic meter, means 0.85 represents its:
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The property by virtue of which a liquid opposes relative motion between its different layers is called:
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The process of diffusion of one liquid into the other through a semipermeable membrane is called:
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Free surface of a liquid tends to contract to the smallest possible area due to force of:
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The kinematic viscosity is the: (AFCAT EKT Mechanical Paper 4 Set 01/2014)
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A piece of metal of specific gravity 7 floats in mercury of specific gravity 13.6. What fraction of its volume is under mercury ? (SSC Jr. Engg. Mechanical 2018)
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If 5.6$m^3$ of oil weighs 46800 N, What is the relative density of the oil?