CE361 - Lecture 02 - 1/17/2009 Water Resources Engineering...

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1/17/2009 1 Water Resources Engineering -Lecture±2 1 Notes by T. Wagener & P. Reed Penn State University Principles of Flow in Hydrosystems 2
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1/17/2009 2 Water Properties – Mass or Weight Mass density or density ρ (rho), is the mass per unit volume [kg/m 3 or Ns 2 /m 4 ]. (Mass density of water at 4°C is 1000kg/m 3 ). Density is often assumed constant, so that water is assumed incompressible in hydrology and hydraulics. Incompressibility does not always mean constant density because salt in water changes the density of water without changing its volume. Specific weight γ (gamma) is the gravitational force (weight) per unit volume of water. (Specific weight of water at 4°C is 9810 N/m 3 or 62.4 lb/ft 3 ). The relationship between density and specific weight is: 3 This is an important characteristic for example when we are dealing with water with different levels of salt content or different temperatures [e.g. Estuaries, density currents, …]. g γ ρ= Why is it Important? Example: Ocean Thermohaline Circulation 4 Evaporation makes water more saline and denser Freezing makes water more saline and denser Cold water is denser than warm water
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1/17/2009 3 Water Properties - Pressure Pressure , p , is the force F acting over an area A Fd F Δ Pressure at a point is equal in all directions. The pressure at depth y (assuming no pressure on the water surface) is 0 lim A P dA dA Δ→ = = 5 P y γ = Water Properties - Pressure 6
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1/17/2009 4 Water Properties - Pressure What is the horizontal pressure (in N per m 2 ) acting at the bottom of Hoover Dam?
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This note was uploaded on 05/05/2009 for the course CE 361 taught by Professor Wagener during the Spring '09 term at Pennsylvania State University, University Park.

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CE361 - Lecture 02 - 1/17/2009 Water Resources Engineering...

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