10-20-Fluids - Chapter 15 Fluids Pressure in a gas F F F A...

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1 Pressure in a gas The molecules of a gas exert a force on every part of the inner wall of the container. The pressure is the magnitude F of the force acting perpendicular to the surface of an object immersed in the liquid, divided by the area A on which the force acts P F A If a small cube is inserted within the container, the cube experiences forces acting perpendicular to each of its six faces. F F F F F F A Unit: 1 Newton/m 2 = 1 Pascal Chapter 15 Fluids Atmospheric pressure Pressure in water Atmospheric pressure at sea level is 1.013 10 5 Newton/m 2 = 1 atmosphere. This is sufficient to crumple a can if the inside air is pumped out. 1 Newton/m 2 = 1 Pascal Pressure in water increases by about 1 atmosphere for every 10m below the surface.
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Pressure depends on depth and density Because the outlined volume of fluid is in equilibrium, the net force acting on it must vanish: P 2 P 1 gh Pressure increases with depth and depends only on depth. P 1 P 2 P 2 A P 1 A mg 0 Ah m V m F 1 = F 2 = 0 1 2 mg F F The mass density is the mass of a given volume of fluid divided by the volume: Then we have hA m The pressure at any point in a fluid depends on the vertical distance h of the point beneath the surface. P A’ = P B’ P A = P B Pa m s m m kg Pa gh P 5 2 3 3 5 1 10 55 . 1 ) 50 . 5 )( / 8 . 9 )( / 10 0 . 1 ( 10 01 . 1 P A = P B matter where the point is located horizontally in the fluid. P 1
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10-20-Fluids - Chapter 15 Fluids Pressure in a gas F F F A...

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