1/17/20092Water Properties – Mass or WeightMass density or densityρ(rho), is the mass per unit volume [kg/m3or Ns2/m4]. (Mass density of water at 4°C is 1000kg/m3).Density is often assumed constant, so that water is assumed iiblih dld h dliIibilitdtincompressible 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 weightγ(gamma) is the gravitational force (weight) per unit volume of water. (Specific weight of water at 4°C is 9810 N/m3or 62.4 lb/ft3).The relationship between densityand specific weightis: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, …].gγρ=Why is it Important? Example: Ocean Thermohaline CirculationEvaporation makes water more saline and denserFreezing makes water more saline and denserCold water is denser than warm water
1/17/20093Water Properties - PressurePressure, p, is the force F acting over an area AFdFΔPressure at a point is equal in all directions.The pressure at depth y (assuming no pressure on the water surface) is0limAPdAdAΔ →==P5yγ=Water Properties - Pressure
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