Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley PowerPoint ® Lectures for University Physics, Twelfth Edition – Hugh D. Young and Roger A. Freedman Lectures by James Pazun Chapter 14 Fluid Mechanics
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Goals for Chapter 14 Pressure, depth, and Pascal’s Law Buoyancy and Archimedes Principle Surface tension Bernoulli’s equation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Densities of common substances—Table 14.1
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The pressure in a fluid Pressure in a fluid is force per unit area. The Pascal is the given SI unit for pressure. Estimate the force act on a paper due to air pressure of 1 atm? Estimate the thickness of atmosphere. Compare your result with data.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Pressure, depth, and Pascal’s Law Pressure is everywhere equal in a uniform fluid of equal depth. What happen if the pressure is not everywhere equal?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Buoyancy and Archimedes Principle The buoyant force is equal to the weight of the displaced fluid. Why?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Surface tension How is it that water striders can walk on water (although they are more dense than the water)?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Capillarity Vertical Force Capillary pressure Capillary rise
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Q: How high could the water been transport in a plant through capillary rise? Typical diameter is about 20 micrometer The calculated height is about 74 cm What happen to plant higher than 74 cm?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Pressure in spherical bubble Energy required for area increasing Work done by pressure
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Fluid flow I The flow lines at left are laminar. The flow at the right is turbulent.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Fluid flow II The incompressibility of fluids allows calculations to be made even as pipes change. The continuity equation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A stream of water emerging from a faucet, the initial cross-section area is known to be 1 cm 2. When the level of water stream drop 5 cm, the stream cross-section is found to reduce to 0.4 cm 2. What is the flow rate from the tap? A.20B. 35C. 50 D. 60E. 70 cm 3 /s
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Bernoulli’s equation Bernoulli’s equation allows the user to consider all variables that might be changing in an ideal fluid.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The Venturi meter (Bernoulli’s Equation IV) Consider Example 14.9.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A 5 meter height, 2 meter radius water tank is filled up with water. If at the bottom of the tank is been drilled with a 1 cm diameter small hole, please estimate the speed of water exiting the tank. A.1 m/sB. 3 m/sC. 7 m/s D. 10 m/sE. 14 m/s
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Danger of Tailing By closely following another car, one can reduce the air drag for saving energy. However, the disrupted air flow will eliminate the negative lift effect on the rear car. This is danger in the case of car racing. If the tailing car does not notify this effect, it might slip out during a turn. H.W. Estimate the negative lifting force on a car with a speed of 100 Km/hr.