Chapter 3 pressure and fluid statics proprietary material. If a point in the fluid is thought of as an infinitesimally small cube, then it follows from the. This is proprietary material solely for authorized instructor use. Hydrostatic pressure distribution in a static fluid and its effects on solid surfaces and on floating and submerged bodies. The hydrostatic pressure can be determined from a control volume analysis of an infinitesimally small cube of fluid. Also, since the pressure at a point is directly proportional to the force. Fluid statics when the fluid velocity is zero, called the hydrostatic condition. In fluid mechanics the term static pressure has several uses. For the general case, the stress on a fluid element or at a point is a tensor. The concept of pressure and the way it is transmitted by fluids was formulated by the french. Fluid statics pressure depends on the depth in the solution not on the lateral coordinate fluid equilibrium transmission of fluid pressure, e. We start this chapter with a detailed discussion of pressure, including absoluteand gage pressures, the pressure at a point, the variation of pressure with depthin a.
Fluid statics is that branch of mechanics of fluids that deals primarily with fluids at. Pressure and fluid statics this chapter deals with forces applied by fluids at rest or in rigidbody motion. This can be demonstrated by considering a small wedgeshaped fluid element of unit length into the page in equilibrium, as shown in fig. In the limit as the fluid wedge shrinks to a point. Most pressuremeasuring devices are calibrated to read zero in the atmosphere, and therefore indicate gage pressure, p gagep absp atm.
The pressure does not vary in a horizontal direction. Discussion in the limit of an infinitesimal cube, we have a fluid particle, with pressure p defined at a point. Pressure and fluid statics pressure at a point pressure at any point in a fluid is the same in all directions. Analysis pascals law states that the pressure applied to a confined fluid increases the pressure throughout by the same amount. Pressure has a magnitude, but not a specific direction, and thus it is a scalar quantity. Introduction to dimensions and units physical properties of fluids specific gravity, viscosity, surface tension, vapor pressure and their influences on fluid motion pressure at a point, pascals law, hydrostatic law. The pressure gradient is a surface force that acts on the sides of the element. The pressure at point 4 is essentially the same as that at point 5 since the speci. Pressure and fluid statics absolute, gage, and vacuum pressures. For a static fluid, pressure varies only with elevation within the fluid. The pressure at the left face of the differential element is 2 2 dy y p p dy y p. Force magnitude and location due to hydrostatic pressure for horizontal and vertical plane walls.
Hence, all free bodies in fluid statics have only normal pressure forces acting on them. Actual pressure at a give point is called the absolute pressure. This is a consequence of the pressure in a fluid remaining constant in the. Gracey, william 1958, measurement of static pressure on aircraft pdf, langley research center. That is, it has magnitude but not a specific direction, and thus it is a scalar quantity. From 1, the pressure at the wall of any vessel is perpendicular to the wall 3. Fluid static definitions, pressure at a point, variation of pressure in. This can be shown by consideration of equilibrium of forces on a fluid element newtons law momentum principle applied to a static fluid f ma 0 for a static fluid i. Fluid statics or hydrostatics is the branch of fluid mechanics that studies fluids at rest and the. Pressure below atmospheric pressure are called vacuum pressure, p vacp atmp abs. Pressure at any point in a fluid is the same in all directions and is transmitted through static fluids without loss pascals principle 2. If a point in the fluid is thought of as an infinitesimally small cube, then it.
Pressure and fluid statics pressure for a static fluid, the only stress is the normal stress since by definition a fluid subjected to a shear stress must deform and undergo motion. The fluid property responsible for those forces is pressure, which is a normal force exerted by a fluid per unit area. Pressure forces pressure gradient assume the pressure vary arbitrarily in a fluid, ppx,y,z,t. Pressure due to depth is p g h, and is the same at any horizontal level of connected fluid. Chapter 2 fluid statics 27 observe that the heights must be in meters. Pressure is defined as the ratio of normal force to area at a point. However, pressure at any point in a fluid is the same in all directions. In the limit when the wedge shrinks to a point, fluid statics. Fluid mechanics pdf notes fm pdf notes smartzworld. For the general case, the stress on a fluid element or at a point is a tensor for a static fluid, ij 0 i j shear stresses 0 ii p xx yy zz i j. A pressure can be identified for every point in a body of fluid, regardless of whether the fluid is in motion.