Chapter 14 Fluid Mechanics PowerPoint Lectures for University Physics, Twelfth Edition Hugh D. Young and Roger A. Freedman Lectures by James Pazun
Goals for Chapter 14 To study density and pressure To consider pressures in a fluid at rest To shout Eureka with Archimedes and overview buoyancy To turn our attention to fluids in motion and calculate the effects of changing openings, height, density, pressure, and velocity
Introduction Submerging bath toys and watching them pop back up to the surface is an experience with Archimedes Principle. Fish move through water with little effort and their motion is smooth. Consider the shark at right it must keep moving for its gills to operate properly.
Density does not depend on the size of the object Density is a measure of how much mass occupies a given volume. Refer to Example 14.1 and Table 14.1 (on the next slide) to assist you. Density values are sometimes divided by the density of water to be tabulated as the unit less quantity, specific gravity.
Densities of common substances Table 14.1
The pressure in a fluid Pressure in a fluid is force per unit area. The Pascal is the given SI unit for pressure. Refer to Figures 14.3 and 14.4. Consider Example 14.2. Values to remember for atmospheric pressure appear near the bottom of page 458.
Pressure, depth, and Pascal s Law Pressure is everywhere equal in a uniform fluid of equal depth. Consider Figure 14.7 and a practical application in Figure 14.8.
Finding absolute and gauge pressure Pressure from the fluid and pressure from the air above it are determined separately and may or may not be combined. Refer to Example 14.3 and Figure 14.9.
There are many clever ways to measure pressure Refer to Figure 14.10. Follow Example 14.4.
Measuring the density of a liquid Have you ever seen the barometers made from glass spheres filled with various densities of liquid? This is their driving science. Refer to Figure 14.13.
Buoyancy and Archimedes Principle The buoyant force is equal to the weight of the displaced fluid. Refer to Figure 14.12.
Buoyancy and Archimedes Principle II Consider Example 14.5. Refer to Figure 14.14 as you read Example 14.5.
Surface tension How is it that water striders can walk on water (although they are more dense than the water)? Refer to Figure 14.15 for the water strider and then Figures 14.16 and 14.17 to see what s occurring from a molecular perspective.
Fluid flow I The flow lines at left in Figure 14.20 are laminar. The flow at the top of Figure 14.21 is turbulent.
Fluid flow II The incompressibility of fluids allows calculations to be made even as pipes change. Refer to Figure 14.22 as you consider Example 14.6.
Bernoulli s equation Bernoulli s equation allows the user to consider all variables that might be changing in an ideal fluid. Refer to Figure 14.23. Consider Problem-Solving Strategy 14.1.
Water pressure in a home (Bernoulli s Principle II) Consider Example 14.7.
Speed of efflux (Bernoulli s Equation III) Refer to Example 14.8.
The Venturi meter (Bernoulli s Equation IV) Consider Example 14.9.
Lift on an airplane wing The first time I saw lift from a flowing fluid, a man was holding a Ping-Pong ball in a funnel while blowing out. A wonderful demonstration to go with the lift is by blowing across the top of a sheet of paper. Refer to Conceptual Example 14.10.
Viscosity and turbulence Figures 14.28, 14.29 When we cease to treat fluids as ideal, molecules can attract or repel one another they can interact with container walls and the result is turbulence.
A curve ball (Bernoulli s equation applied to sports) Bernoulli s equation allows us to explain why a curve ball would curve, and why a slider turns downward. Consider Figure 14.31.