Technology & Engineering
Fluid Pressure Force
Fluid pressure force refers to the force exerted by a fluid, such as a liquid or gas, on an object immersed in it. It is determined by the density and depth of the fluid and is perpendicular to the surface of the object. This force is a crucial consideration in various engineering applications, including hydraulic systems and fluid dynamics.
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9 Key excerpts on "Fluid Pressure Force"
- Ravi Doddannavar, Andries Barnard, Jayaraman Ganesh(Authors)
- 2005(Publication Date)
- Newnes(Publisher)
2 Pressure and flow 2.1 Objectives On reading this chapter, the student will be able to: • Explain and understand the various terms and definitions used in hydraulics • Understand the significance of Pascal’s law and its applications • Understand the importance of flow and pressure in hydraulics. 2.2 Pressure Pressure along with flow is one of the key parameters involved in the study of hydraulics. Pressure in a hydraulic system comes from resistance to flow. This can be best understood from Figure 2.1. Figure 2.1 Pressure buildup in a hydraulic system Consider the flow from a hydraulic pump as shown. Here the pump produces only flow and not pressure. However any restriction in the flow from the pump results in the formation of pressure. This restriction or resistance to flow normally results from the load induced in the actuator. The various conductors and components of the hydraulic system Pressure and flow 17 such as pipes and elbows also act as points of resistance and contribute to the generation of pressure in the system. Pressure ( P ) is defined as the force ( F ) acting normally per unit area ( A ) of the surface and is given by the equation: F P A = Pressure in the SI unit is measured in terms of N/m 2 also known as a Pascal. Pressure can also be expressed in terms of bar, where 5 2 1 bar = 10 N/m Pressure in the US unit is measured in terms of lb/in. 2 or psi, where 2 1 psi = 0.0703 kg/cm 2.2.1 Pressure in fluids Fluids are composed of molecules, which are in continuous random motion. These molecules move throughout the volume of the fluid colliding with each other and with the walls of the container as a result of which the molecules undergo a change in momentum. Now, let us consider a surface within the fluid which is impacted by a large number of molecules. This results in a transfer in momentum from the molecules to the surface.
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
C H A P T E R 1 4 Fluids 14-1 FLUIDS, DENSITY, AND PRESSURE Learning Objectives After reading this module, you should be able to . . . 14.01 Distinguish fluids from solids. 14.02 When mass is uniformly distributed, relate density to mass and volume. 14.03 Apply the relationship between hydrostatic pres- sure, force, and the surface area over which that force acts. ● The density of any material is defined as the material’s mass per unit volume: ρ = Δm ΔV . Usually, where a material sample is much larger than atomic dimensions, we can write this as ρ = m V . ● A fluid is a substance that can flow; it conforms to the boundaries of its container because it cannot with- stand shearing stress. It can, however, exert a force perpendicular to its surface. That force is described in terms of pressure p: p = ΔF ΔA , in which ∆F is the force acting on a surface element of area ∆A. If the force is uniform over a flat area, this can be written as p = F A . ● The force resulting from fluid pressure at a particular point in a fluid has the same magnitude in all directions. Key Ideas What Is Physics? The physics of fluids is the basis of hydraulic engineering, a branch of engineering that is applied in a great many fields. A nuclear engineer might study the fluid flow in the hydraulic system of an aging nuclear reactor, while a medical engineer might study the blood flow in the arteries of an aging patient. An environmental engineer might be concerned about the drainage from waste sites or the efficient irrigation of farmlands. A naval engineer might be concerned with the dangers faced by a deep-sea diver or with the possibility of a crew escaping from a downed submarine. An aeronautical engineer might design the hydraulic systems control- ling the wing flaps that allow a jet airplane to land. Hydraulic engineering is also applied in many Broadway and Las Vegas shows, where huge sets are quickly put up and brought down by hydraulic systems.
eBook - PDFPhysics of Continuous Matter
Exotic and Everyday Phenomena in the Macroscopic World
- B. Lautrup(Author)
- 2011(Publication Date)
- CRC Press(Publisher)
The component acting tangentially to the surface is called a shear force or a traction force . Fluids in motion, and solids at rest or in motion, are able to sustain shear forces, whereas fluids at rest cannot. Should shear forces arise in a fluid at rest, it will begin to flow until it again reaches mechanical equilibrium without shear forces. In this chapter we shall first investigate the basic properties of pressure, and afterward develop the mathematical formalism that permits us to analyze hydrostatic equilibrium in the sea and the atmosphere. Along the way we shall recapitulate some basic rules of thermody-namics. In the following chapters we shall continue to study the implications of hydrostatic equilibrium for balloons and ships, and the shapes of large fluid bodies subject only to gravity and small fluid bodies subject mainly to surface tension. 2.1 What is pressure? Pressure is defined as normal force per unit of area . The SI–unit for pressure is accordingly newton per square meter, but was in 1971 given the name pascal and the special symbol Pa D N m 2 . Earlier units for pressure were the bar ( 1 bar D 10 5 Pa) and the standard atmosphere ( 1 atm D 101; 325 Pa), which is close to the average air pressure at sea level. Modern television weather forecasters are now abandoning the older units and tend to quote air pressure in hectopascals rather than in millibars, even if they are exactly the same ( 1 hPa D 100 Pa D 10 3 bar D 1 millibar). 22 PHYSICS OF CONTINUOUS MATTER Case: The incompressible sea A p 0 p h 6 pA ? p 0 A r ? Mg 0 A column of sea water. The pres-sure difference between bottom and top must carry the weight of the water in the box. Notice that the sum of the forces vanishes. Before presenting a formal definition of the pressure field, we use simple arguments to cal-culate it in the sea. In the first approximation, water is incompressible and has everywhere the same mass density 0 .
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
406 Fluids 14.1 FLUIDS, DENSITY, AND PRESSURE Learning Objectives After reading this module, you should be able to . . . 14.1.1 Distinguish fluids from solids. 14.1.2 When mass is uniformly distributed, relate density to mass and volume. 14.1.3 Apply the relationship between hydrostatic pres- sure, force, and the surface area over which that force acts. Key Ideas What Is Physics? The physics of fluids is the basis of hydraulic engineering, a branch of engineering that is applied in a great many fields. A nuclear engineer might study the fluid flow in the hydraulic system of an aging nuclear reactor, while a medical engineer might study the blood flow in the arteries of an aging patient. An environmental engineer might be concerned about the drainage from waste sites or the efficient irrigation of farmlands. A naval engineer might be concerned with the dangers faced by a deep-sea diver or with the possibility of a crew escaping from a downed submarine. An aeronautical engineer might design the hydraulic systems control- ling the wing flaps that allow a jet airplane to land. Hydraulic engineering is also applied in many Broadway and Las Vegas shows, where huge sets are quickly put up and brought down by hydraulic systems. Before we can study any such application of the physics of fluids, we must first answer the question “What is a fluid?” What Is a Fluid? A fluid, in contrast to a solid, is a substance that can flow. Fluids conform to the boundaries of any container in which we put them. They do so because a fluid cannot sustain a force that is tangential to its surface.
- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
C H A P T E R 14 After reading this module, you should be able to . . . 14.1.1 Distinguish fluids from solids. 14.1.2 When mass is uniformly distributed, relate density to mass and volume. 14.1.3 Apply the relationship between hydrostatic pressure, force, and the surface area over which that force acts. 14.1 FLUIDS, DENSITY, AND PRESSURE KEY IDEAS 1. The density of any material is defined as the material’s mass per unit volume: ρ = Δm ____ ΔV . Usually, where a material sample is much larger than atomic dimensions, we can write this as ρ = m __ V . 2. A fluid is a substance that can flow; it conforms to the boundaries of its con- tainer because it cannot withstand shearing stress. It can, however, exert a force perpendicular to its surface. That force is described in terms of pressure p: p = ΔF _ ΔA , in which ∆F is the force acting on a surface element of area ∆A. If the force is uniform over a flat area, this can be written as p = F _ A . 3. The force resulting from fluid pressure at a particular point in a fluid has the same magnitude in all directions. LEARNING OBJECTIVES 383 What Is Physics? The physics of fluids is the basis of hydraulic engineering, a branch of engineering that is applied in a great many fields. A nuclear engineer might study the fluid flow in the hydraulic system of an aging nuclear reactor, while a medical engineer might study the blood flow in the arteries of an aging patient. An environmental engineer might be concerned about the drainage from waste sites or the efficient irrigation of farmlands. A naval engineer might be concerned with the dangers faced by a deep-sea diver or with the possibility of a crew escaping from a downed submarine. An aeronautical engineer might design the hydraulic systems con- trolling the wing flaps that allow a jet airplane to land. Hydraulic engineering is also applied in many Broadway and Las Vegas shows, where huge sets are quickly put up and brought down by hydraulic systems.
- Jonathan Wickert, Jonathan Wickert, Kemper Lewis(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Mechanical engineers apply the principles of fluids engineering to applica-tions such as aerodynamics, biomedical engineering, microfluidics, and sports engineering. The flow of fluids through pipes, hoses, and ducts is an example of this diversity. In addition to the distribution of water, gasoline, natural gas, and air through piping systems, the principles behind fluid flow in pipes can be applied in studies of the human circulatory and respiratory systems. The primary variables, symbols, and conventional units that are used in this chapter are summarized in Table 6.4, and the key equations are listed in Table 6.5. Table 6.4 Quantities, Symbols, and Units that Arise in Fluids Engineering Quantity Conventional Symbols Conventional Units Area A m 2 Coefficient of drag C D — Coefficient of lift C L — Density r kg/m 3 Force Buoyancy F B N Drag F D N Lift F L N Weight w N Length Characteristic length l m Pipe length L m Mach number Ma — Pressure p Pa Reynolds number Re — Shear stress t Pa Time interval D t s Velocity v , v avg , v max m/s Viscosity m kg/(m · s) Volume V , D V L, m 3 Volumetric flow rate q L/s, m 3 /s Copyright 201 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 264 Chapter 6 Fluids Engineering The buoyancy force develops when an object is immersed in a fluid, and it is related to the weight of the displaced fluid.
eBook - PDFAdvanced Transport Phenomena
Analysis, Modeling, and Computations
- P. A. Ramachandran(Author)
- 2014(Publication Date)
- Cambridge University Press(Publisher)
161 4.1 Forces on fluids and their representation of the fluid are needed. This is the focus of this section. The forces acting on a fluid can be represented as Forces acting on the system = Gravity + Pressure + Viscous forces The pressure and viscous forces act over the control surfaces; gravity acts over the control volume. Since gravity is a volume force, the representation is straightforward: Gravity forces acting on the system = V ρ g dV For a differential control volume ρ is assigned as the point value and hence Gravity force per unit volume = ρ g 4.1.1 Pressure forces We now examine the nature of pressure force in the following subsection. We pose the following question. What is pressure and why is it a scalar quantity? Before answering this we need to answer the following question. What is a fluid? A fluid by definition is a material that cannot resist a shear force (a force applied tangen-tially). It continues to flow under the action of a shear force. Hence in a static fluid only normal forces can exist; shear or tangential stresses cannot exist. The normal stress acting on a static fluid is defined as the fluid pressure. It acts equally in all directions, the famous Pascal principle, and hence it can be represented by a scalar field. It is also compressive in nature as indicated earlier in Chapters 1 and 2. The fact that pressure is a scalar and acts equally in all directions is demonstrated by balancing forces on a wedge-shaped control volume of the fluid shown in Fig. 4.1 . We take the control volume in 2D for easy visualization. (The extension to 3D is straightforward.) Let the pressure on the face AC be p . Then the pressure force on AC is pAC per unit width and in the inward normal direction shown in Fig. 4.1 . The component of this in the minus x -direction is pAC cos α . A C B p x p pAC cos α α Figure 4.1 An illustration of a wedge-or prism-shaped control volume to examine the nature of the pressure force.
eBook - PDFFluid Power Circuits and Controls
Fundamentals and Applications
- John S. Cundiff(Author)
- 2001(Publication Date)
- CRC Press(Publisher)
However, it is the practice within some engineering application areas to refer to pressure as head, specified in units of length. This length term refers to the pressure that results at the bottom of a column of water of equivalent height. For the most part, engineers in the fluid power industry convert head to pressure. The density of a fluid is often referred to in terms of specific gravity. Specific gravity, by definition, is the ratio of the specific weight of the fluid in question to that of water at standard conditions (standard pressure 760 mm Hg and 1 m 0.3 m FIGURE 2.1 Static pressure developed by a column of fluid. P ρ g h ⋅ ⋅ = 18 Fluid Power Circuits and Controls temperature of 4°C). We can now modify the static pressure equation and introduce specific gravity as (2.6) where = specific gravity = density of water Applying this equation to the original example and rearranging the terms, we can describe the of the fluid in the column. Solving for , we have (2.7) We know that is 1000 kg/m 3 , and the measured pressure is P = 8.83 kPa. The specific gravity of the fluid in question is Returning to the original fluid column example, there is one additional point to be made. The hydrostatic pressure acting on the bottom of the column acts normal to the surface of the bottom of the column. We can now integrate the hydrostatic pressure over the bottom of the fluid column to determine the total weight of fluid. or, in simplified form, (2.8) If the column has an internal diameter of 30.0 cm, Excluding the container, any support for this fluid column must be capable of withstanding a total force of 624 N (140 lb f ). In most hydraulic systems, static pressure resulting from fluid columns or a depth of fluid in a reservoir is of minor importance.
eBook - PDFFundamentals of Physics
Mechanics, Relativity, and Thermodynamics
- R. Shankar(Author)
- 2014(Publication Date)
- Yale University Press(Publisher)
chapter 20 Fluids 20.1 Introduction to fluid dynamics and statics This is a relatively simple topic. If you took any kind of high school physics, you would have seen fluids. Whenever I say fluid, you are free to imagine water or oil. 20.1.1 Density and pressure Let us begin with a basic property of the fluid, the density, denoted by ρ . The density of water is ρ w = 1, 000 kg / m 3 . The more subtle concept is the one of pressure . If you dive down to the bottom of a swimming pool, the pressure goes up. What is the formal definition of pressure? That’s what I want to explain. If we pick a point in the fluid and say the pressure there is such and such, we mean the following. Say you get into that fluid and you want to carve out a little space for yourself, maybe a glass cube, and you want to live inside that cube. The water is trying to push you in from all sides and compress this cube. You therefore have to push out on all the walls. If the force you exert on a wall is some F and the area of that wall is A , that ratio is the pressure. The pressure will not depend on which wall you choose, provided the cube you are in is infinitesimal. The pressure is an intensive measure of how hard the water is trying to push in. Even if you don’t insert the cube, that pressure is still there, but one way to measure the pressure 335 336 Fluids Figure 20.1 A gas in a cylinder with a massless piston of area A on top. The mass m exerts a force F = mg and a pressure P = mg A Pascals. is to try to go in there and push the fluid out and ask how hard it pushes back. The unit of pressure is N / m 2 and is called a Pascal . Here’s another example of pressure. You have a gas inside a cylinder as shown in Figure 20.1, with a massless piston at the top. The pressure of the gas and the pressure of the outside world are the same. But if you want to increase the pressure in the gas, you can put some extra weights on the piston.
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