1. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 1 Lecture 21 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 21 Fluid Dynamics

2. Introduction Section 0 Lecture 1 Slide 2 Lecture 21 Slide 2 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet *Homework Handout

3. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 3 Lecture 21 Slide 3 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Dennison’s Laws of Fluids When push comes to shove, fluids are just like other stuff. Pascal’s Principle: Pressure extends uniformly in all directions in a fluid. Boyle’s Law: Work on a fluid equals PΔV Bernoulli’s Principle: Conservation of energy for fluids

4. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 4 Lecture 21 Slide 4 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 21 Fluid Dynamics Fluids in Motion

5. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 5 Lecture 21 Slide 5 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Fluids in Motion The flow of a fluid is affected by many factors, including the viscosity of the fluid, a measure of the frictional effects within the fluid. –The larger the viscosity, the larger the frictional forces between different layers of the fluid. –Molasses has a larger viscosity than water. Size also has an effect; for example, a stream’s current is faster where the stream is narrow. –Rate of flow, for example of water through a stream or pipe, is volume divided by time. –Gallons per minute; liters per second; cubic meters per second.

6. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 6 Lecture 21 Slide 6 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Flow Rate The volume of a portion of water of length L flowing past some point in a pipe is the product of the length times the cross-sectional area A, or LA. The rate at which water moves through the pipe is this volume divided by time: LA / t. Since L / t = v, the rate of flow = vA.

7. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 7 Lecture 21 Slide 7 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 If the flow is continuous, the rate of flow must be the same at any point along the pipe. If the cross-sectional area A decreases, the speed v must increase to maintain the same rate of flow. Flow Rate

8. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 8 Lecture 21 Slide 8 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The speed will also usually be greatest near the middle of the stream or pipe (edge effects). The fluid can be imagined as flowing in layers (streamlines in laminar flow). Because of frictional or viscous forces, a thin layer that does not move is usually next to the walls of the pipe or trough (boundary layer). The fluid speed increases as the distance from the wall increases. Each layer moves more slowly than the one above continuity and flow. Flow Rate a Different Points in the Cross Section

9. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 9 Lecture 21 Slide 9 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 For a fluid with low viscosity, the transition to the maximum speed occurs over a short distance from the wall. For a fluid with high viscosity, the transition takes place over a larger distance, and the speed may vary throughout the pipe or trough. Flow Rate and Viscosity

10. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 10 Lecture 21 Slide 10 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 How can a ball be suspended in mid-air? A ball is suspended in an upward-moving column of air produced by a hair dryer. The air pressure is smallest in the center of the column, where the air is moving the fastest.

11. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 11 Lecture 21 Slide 11 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 21 Fluid Dynamics Fluids in Motion Turbulent Flow

12. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 12 Lecture 21 Slide 12 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Laminar flow is smooth flow, with no eddies or other disturbances. –The streamlines are roughly parallel. –The speeds of different layers may vary, but one layer moves smoothly past another. Turbulent flow does have eddies and whorls; the streamlines are no longer parallel. Laminar vs Turbulent Flow

13. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 13 Lecture 21 Slide 13 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Turbulent flow increases the fluid’s resistance to flowing through a pipe. Higher speeds are more likely to exhibit turbulent flow. Higher viscosities are less likely to exhibit turbulent flow. Examples: –Narrowing of a stream –Water from a spigot –Smoke rising from a cigarette or candle. Laminar vs Turbulent Flow L T

14. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 14 Lecture 21 Slide 14 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Huge example: the famous red spot of Jupiter –Whorls and eddies can be seen in the atmospheric gases. –The giant red spot is thought to be a giant and very stable atmospheric eddy. Laminar vs Turbulent Flow

15. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 15 Lecture 21 Slide 15 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Red Spot –Hundreds of Years Old Storm

16. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 16 Lecture 21 Slide 16 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009

17. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 17 Lecture 21 Slide 17 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 21 Fluid Dynamicss Bernoulli’s Principle: Conservation of Energy for Fluids

18. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 18 Lecture 21 Slide 18 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Bernoulli’s Principle How does a large passenger jet manage to get off the ground? What forces keep it in the air? How is a ball suspended in mid-air by a leaf blower? What happens if we do work on a fluid? Bernoulli’s principle applies conservation of energy to the flow of fluids: The sum of the pressure plus the kinetic energy per unit volume of a flowing fluid must remain constant.

19. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 19 Lecture 21 Slide 19 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 How does pressure vary in pipes and hoses? Will the pressure be greatest in the narrow section or the wide section? The speed will be greater in the narrow section. To keep the sum P + 1/2 dv 2 constant, the pressure must be larger where the fluid speed is smaller (h is fixed). If the speed increases, the pressure decreases. (This goes against our intuition.) This can be shown using vertical open pipes as pressure gauges. The height of the column of water is proportional to the pressure. Pressure Changes with Area

20. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 20 Lecture 21 Slide 20 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Pitot Tube

21. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 21 Lecture 21 Slide 21 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 19 Fluids Bernoulli’s Principle: Physics of Flight

22. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 22 Lecture 21 Slide 22 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Pressure decreases with increasing speed. Blowing across the top of a limp piece of paper causes the paper to rise, demonstrating Bernoulli’s principle.

23. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 23 Lecture 21 Slide 23 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 How does an airplane wing work? The shape and tilt of the wing cause the air to move faster across the top than across the bottom. This causes a lower pressure on the top of the wing. The pressure difference produces a net upward force, or lift, acting on the wing. When the lift balances the airplane’s weight, the airplane will fly.

24. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 24 Lecture 21 Slide 24 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Airplane Lift

25. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 25 Lecture 21 Slide 25 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Aerodynamics of Baseball

26. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 26 Lecture 21 Slide 26 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Why does a curveball curve? The whirlpool of air created by the spin of the ball causes the air to move more rapidly on one side than the other. The difference in pressure produces a force toward the lower-pressure, higher- airspeed side. Aerodynamics of Baseball

27. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 27 Lecture 21 Slide 27 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Aerodynamics of Baseball

28. Fluid Dynamics Introduction Section 0 Lecture 1 Slide 28 Lecture 21 Slide 28 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology Next Lab/Demo: Rotational Motion Fluids Thursday 1:30-2:45 ESLC 46 Ch 8 and 9 Next Class: Friday 10:30-11:20 BUS 318 room Review Ch 9 Read Ch 10