Chapter 13 Lecture

Chapter 13: Fluid Mechanics

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Goals for Chapter 13

•  To study density and pressure in a fluid. •  To apply Archimedes principle of buoyancy. •  To describe surface tension and capillary action •  To study and solve Bernoulli's equation for fluid

flow. •  To see how real fluids differ from ideal fluids

(turbulence and viscosity).

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Density – Example 13.1

•  Density is a macroscopic measurable that gives us some insight to atomic spacing.

•  Refer to Table 13.1 and the example worked out on page 396 in your text.

•  At right, liquids of different densities separate with denser liquids lower in the glass.

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Pressure In a Fluid – Figure 13.3

•  P = F/A

•  The pressure is equal to force (in N) per unit area (in m2).

•  A new derived unit N/m2 = 1 Pascal = 1 Pa

•  Atmospheric pressure is 1 atm = 760 mm Hg = 14.7 lb/in2 = 760 mm Hg = 101325 Pa = 1.013 bars = 101.3 millibars.

•  Refer to Example 13.2. © 2016 Pearson Education, Inc.

The Pressure in a Fluid – Figure 13.6

•  The pressure in any fluid at the same elevation will be the same regardless of the shape or size of the container.

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Pascal's Law – Figure 13.7

•  In a closed system, pressures transmitted to a fluid are identical to all parts of the container.

•  Variations in the pressure are due only to the depth of the fluid.

•  This principal is vital to mechanical devices like lifts and brakes.

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Determining Absolute or Gauge Pressure –Example 13.4 •  The gauge pressure in exerted by the system.

•  Absolute pressure includes the local atmospheric pressure.

•  Refer to Example 13.4.

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Archimedes's Principle – Figure 13.15

•  An object submersed in a fluid experiences buoyant force equal to the mass of any fluid it displaces.

•  An object can experience buoyant force greater than its mass and float. Even if it sinks, it would weigh measurably less.

•  Refer to Example 13.7.

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Surface Tension – Figures 13.21 and 13.23

•  Also, refer to Example 13.8.

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Bernoulli's Equation – Figure 13.29

•  A comprehensive work for ideal fluids, Bernoulli accounted for:

•  fluid densities

•  height differences

•  different pipe diameters

•  exterior pressures at the inlet and outlet

•  Refer to Problem Solving Strategy 13.1 and Example 13.9.

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Bernoulli's Equation Applied II – Figures 13.33 •  The venturi tube allows pressure measurement

"in line."

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Bernoulli's Equation Applied I – Figures 13.33 •  Blood flow characteristics are changed

dramatically by plaque.

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Bernoulli's Equation Applied III – Figures 13.35 •  Sports abounds with good examples but the very

best direct application of Bernoulli's equation is pitching in baseball.

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