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Unformatted text preview: Chapter 11 Fluid Statics 11-1 Chapter 11 FLUID STATICS Fluid Statics: Hydrostatic Forces on Plane and Curved Surfaces 11-1C The resultant hydrostatic force acting on a submerged surface is the resultant of the pressure forces acting on the surface. The point of application of this resultant force is called the center of pressure. 11-2C Yes, because the magnitude of the resultant force acting on a plane surface of a completely submerged body in a homogeneous fluid is equal to the product of the pressure P C at the centroid of the surface and the area A of the surface. The pressure at the centroid of the surface is C C gh P P r + = where C h is the vertical distance of the centroid from the free surface of the liquid. 11-3C There will be no change on the hydrostatic force acting on the top surface of this submerged horizontal flat plate as a result of this rotation since the magnitude of the resultant force acting on a plane surface of a completely submerged body in a homogeneous fluid is equal to the product of the pressure P C at the centroid of the surface and the area A of the surface. 11-4C Dams are built much thicker at the bottom because the pressure force increases with depth, and the bottom part of dams are subjected to largest forces. 11-5C The horizontal component of the hydrostatic force acting on a curved surface is equal (in both magnitude and the line of action) to the hydrostatic force acting on the vertical projection of the curved surface. 11-6C The vertical component of the hydrostatic force acting on a curved surface is equal to the hydrostatic force acting on the horizontal projection of the curved surface, plus (minus, if acting in the opposite direction) the weight of the fluid block. 11-7C The resultant hydrostatic force acting on a circular surface always passes through the center of the circle since the pressure forces are normal to the surface, and all lines normal to the surface of a circle pass through the center of the circle. Thus the pressure forces form a concurrent force system at the center, which can be reduced to a single equivalent force at that point. If the magnitudes of the horizontal and vertical components of the resultant hydrostatic force are known, the tangent of the angle the resultant hydrostatic force makes with the horizontal is H V F F / tan = a . Chapter 11 Fluid Statics 11-2 11-8 A car is submerged in water. The hydrostatic force on the door and its line of action are to be determined for the cases of the car containing atmospheric air and the car is filled with water. Assumptions 1 The bottom surface of the lake is horizontal. 2 The door can be approximated as a vertical rectangular plate. 3 The pressure in the car remains at atmospheric value since there is no water leaking in, and thus no compression of the air inside. Therefore, we can ignore the atmospheric pressure in calculations since it acts on both sides of the door....
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