FluidMechanics - Fluid Mechanics Let us now look at the...

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Let us now look at the properties inherent in a fluid. A fluid differs from a solid in that it cannot support a shear stress. In this sense, both liquids and gases can be described as fluids (in fact, under certain extreme conditions, even solids exhibit fluid-like properties). The density of a fluid is defined as its mass per unit volume ρ = m V (18.1) Density is considered to be inherent to the fluid and can be used to characterize it. The specific gravity of a fluid is the ratio of its density to that of water. It is a dimensionless number. Since the density of water is defined to be 1 gm/cm 3 , the specific gravity of a fluid is the density without the units, if the density was also given in gm/cm 3 . Pressure When a body is submerged in a fluid, the fluid exerts a force perpendicular to the surface of the body at each point on the surface. However, for a fluid, the force does not necessarily need to be a constant over the whole surface. This leads us to a more refined definition of pressure. We define the pressure p at a point in a fluid as the ratio of the normal force dF on a small area dA around that point, to the area p dF dA = (18.2) From this definition we can immediately see that pressure also has units of Pascals. The pressure due to a fluid tends to compress a body. The ratio of the pressure to the fractional decrease in volume is called the bulk modulus B p V V = - The inverse of the bulk modulus is called the compressibility , k . Variation of Pressure with Depth
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This note was uploaded on 07/24/2009 for the course PHY 092342 taught by Professor Knott during the Spring '09 term at Cosumnes River College.

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FluidMechanics - Fluid Mechanics Let us now look at the...

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