homework1_solns - Homework 1 solutions Fluid Mechanics CE...

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Homework 1 solutions Fluid Mechanics CE 3502 Fall, 2008 (1) What is the ratio of the kinematic viscosity of air to that of sea water at 3.3% salinity at standard pressure and a temperature of 10°C? What is the ratio of the dynamic viscosity of air to that of sea water for the same conditions? Find: (a) Ratio of dynamic viscosity of air to that of water. (b) Ratio of kinematic viscosity of air to that of water. Air and sea water (3.3% salinity) are at 10°C, under standard pressure. Solution: From Table A.3, μ air, 10°C, std.press. = 1.76 x 10 5 N*s/m 2 ; ν air, 10°C, std.press. = 1.41 x 10 5 m 2 /s; From Table A.4, μ sea water, 10°C, 3.3% salinity. = 1.4 x 10 3 N*s/m 2 ; ν sea water, 10°C, 3.3% salinity. = 1.4 x 10 6 m 2 /s; μ air, 10°C, std.press. / μ sea water, 10°C, 3.3% salinity. = (1.76 x 10 -5 N*s/m 2 ) / (1.4 x 10 -3 N*s/m 2 ) = 1.26 x 10 -2 ν air, 10°C, std.press. / ν sea water, 10°C, 3.3% salinity. = (1.41 x 10 -5 m 2 /s ) / (1.4 x 10 -6 m 2 /s ) = 10.1 It makes sense that the dynamic viscosity of air is less than that of water – it is much easier to shear air than water. Do you find it odd that the kinematic viscosity of air is greater than that of water? We have not yet talked about where kinematic viscosity is most useful; only dynamic viscosity. Later in the semester the situations where kinematic viscosity is more relevant than dynamic viscosity will become apparent. (2) A water bug of mass m = 0.389 x 10 -3 kg is suspended on the surface of a pond by surface tension (water does not wet the legs). The bug has six legs, and each leg is in contact with the water over the same length. What is the minimum length in which each leg is in contact with the water? Given:
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homework1_solns - Homework 1 solutions Fluid Mechanics CE...

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