#### Properties of Fluids: Screencasts

Defines fluids and describes some characteristics of fluids.

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Explains two fluid properties: density and bulk modulus.

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Explains two fluid properties: vapor pressure and surface tension.

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##### Important Equations:

Density \(\rho\) of an ideal gas can be calculated by rearranging the ideal gas law.

\[ \rho = \frac{RM}{RT} \]

where \(P\) is pressue, \(M\) is molecular mass, \(R\) is the gas constant, and \(T\) is the absolute temperature.

Specific volume \(v\):

\[ v = \frac{1}{\rho}\]

Specific gravity \((SG)\) is a dimensionless form of density. It compares the density of the material of interest to a reference material, which is most commonly water.

\[SG = \frac{\rho_f}{\rho_{ref}} \]

where \(\rho_f\) is the density of the material of interest and \(\rho_{ref}\) is the density of the reference material.

Specific weight \( (\gamma) \):

\[ \gamma = \rho g \]

where \(g\) is the acceleration due to gravity.

The bulk modulus \( (E_v) )\ is a fluid property that describes that compressibility of the fluid.

\[ E_v = -V \frac{dP}{dV} = \rho \frac{dP}{d\rho} \]

where \(V\) is volume, \( dP \) is differential pressure, \(dV\) is differential volume, and \( d \rho \) is differential density.

Surface tension \((\sigma)\) is tensile force at interfaces that can be derived for a fluid droplet in an immiscible fluid.

\[\Delta P = \frac{2\sigma}{r} \]

where \( \Delta P \) is a pressure change, and \(r\) is the radius of the droplet.

One of the common effects of the surface tension is capillary rise. The height of capillary rise \((h)\) can be derived as follows:

\[ h = 2\sigma \cos(\frac{\theta}{\gamma r}) \]

where \(\theta\) is the contact angle between the liquid and the capillary tube and \(r\) is the radius of the capillary tube.