Chapter 14 | Fluid Mechanics 685 14 | FLUID MECHANICS 850hpa Heights (in Dyn. meters) Forecast valid 19Z03Jul2014 48N 42N 36N 30N- 24N 18N- .O! 90W 80W 70W 60W 1420 1460 1500 1540 1580 1620 Figure 14.1 This pressure map (left) and satellite photo (right) were used to model the path and impact of Hurricane Arthur as it traveled up the East Coast of the United States in July 2014. Computer models use force and energy equations to predict developing weather patterns. Scientists numerically integrate these time-dependent equations, along with the energy budgets of long- and short-wave solar energy, to model changes in the atmosphere. The pressure map on the left was created using the Weather Research and Forecasting Model designed at the National Center for Atmospheric Research. The colors represent the height of the 850-mbar pressure surface. (credit left: modification of work by The National Center for Atmospheric Research; credit right: modification of work by NRL Monterey Marine Meteorology Division, The National Oceanic and Atmospheric Administration) Chapter Outline 14.1 Fluids, Density, and Pressure 14.2 Measuring Pressure 14.3 Pascal's Principle and Hydraulics 14.4 Archimedes' Principle and Buoyancy 14.5 Fluid Dynamics 14.6 Bernoulli's Equation 14.7 Viscosity and Turbulence Introduction Picture yourself walking along a beach on the eastern shore of the United States. The air smells of sea salt and the sun warms your body. Suddenly, an alert appears on your cell phone. A tropical depression has formed into a hurricane. Atmospheric pressure has fallen to nearly 15% below average. As a result, forecasters expect torrential rainfall, winds in excess of 100 mph, and millions of dollars in damage. As you prepare to evacuate, you wonder: How can such a small drop in pressure lead to such a severe change in the weather? Pressure is a physical phenomenon that is responsible for much more than just the weather. Changes in pressure cause ears
686 Chapter 14 | Fluid Mechanics to "pop" during takeoff in an airplane. Changes in pressure can also cause scuba divers to suffer a sometimes fatal disorder known as the "bends," which occurs when nitrogen dissolved in the water of the body at extreme depths returns to a gaseous state in the body as the diver surfaces. Pressure lies at the heart of the phenomena called buoyancy, which causes hot air balloons to rise and ships to float. Before we can fully understand the role that pressure plays in these phenomena, we need to discuss the states of matter and the concept of density. 14.1 | Fluids, Density, and Pressure Learning Objectives By the end of this section, you will be able to: · State the different phases of matter . Describe the characteristics of the phases of matter at the molecular or atomic level · Distinguish between compressible and incompressible materials . Define density and its related SI units . Compare and contrast the densities of various substances . Define pressure and its related SI units · Explain the relationship between pressure and force · Calculate force