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Unformatted text preview: Chapter 11 Fluids 11.1 Mass Density DEFINITION OF MASS DENSITY The mass density of a substance is the mass of a substance divided by its volume: V m = ρ SI Unit of Mass Density: kg/m 3 11.1 Mass Density 11.1 Mass Density Example 1 Blood as a Fraction of Body Weight The body of a man whose weight is 690 N contains about 5.2x103 m 3 of blood. (a) Find the blood’s weight and (b) express it as a percentage of the body weight. ( 29 ( 29 kg 5 . 5 m kg 1060 m 10 2 . 5 3 3 3 = × = = ρ V m 11.1 Mass Density ( 29 ( 29 N 54 s m 80 . 9 kg 5 . 5 2 = = = mg W (a) (b) % 8 . 7 % 100 N 690 N 54 Percentage = × = 11.2 Pressure A F P = SI Unit of Pressure: 1 N/m 2 = 1Pa Pascal 11.2 Pressure Example 2 The Force on a Swimmer Suppose the pressure acting on the back of a swimmer’s hand is 1.2x10 5 Pa. The surface area of the back of the hand is 8.4x103 m 2 . (a)Determine the magnitude of the force that acts on it. (b) Discuss the direction of the force. 11.2 Pressure A F P = ( 29 ( 29 N 10 . 1 m 10 4 . 8 m N 10 2 . 1 3 2 3 2 5 × = × × = = PA F Since the water pushes perpendicularly against the back of the hand, the force is directed downward in the drawing. 11.2 Pressure Atmospheric Pressure at Sea Level: 1.013x10 5 Pa = 1 atmosphere 11.3 Pressure and Depth in a Static Fluid 1 2 = = ∑ mg A P A P F y mg A P A P + = 1 2 ρ V m = 11.3 Pressure and Depth in a Static Fluid Vg A P A P ρ + = 1 2 Ah V = Ahg A P A P ρ + = 1 2 hg P P ρ + = 1 2 11.3 Pressure and Depth in a Static Fluid Conceptual Example 3 The Hoover Dam Lake Mead is the largest wholly artificial reservoir in the United States. The water in the reservoir backs up behind the dam for a considerable distance (120 miles). Suppose that all the water in Lake Mead were removed except a relatively narrow vertical column. Would the Hoover Same still be needed to contain the water, or could a much less massive structure do the job? 11.3 Pressure and Depth in a Static Fluid Example 4 The Swimming Hole Points A and B are located a distance of 5.50 m beneath the surface of the water. Find the pressure at each of these two locations. 11.3 Pressure and Depth in a Static Fluid ( 29 ( 29 ( 29 ( 29 Pa 10 55 . 1 m 50 . 5 s m 80 . 9 m kg 10 00 . 1 Pa 10 01 . 1 5 2 3 3 pressure c atmospheri 5 2 × = × + × = P gh P P ρ + = 1 2 11.4 11....
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 Spring '07
 Russell
 Physics, Fluid Dynamics, Mass, mass density

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