# ps5 - Zoology 440 Biomechanics 1999 Problem Set 5. Some...

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Zoology 440 Biomechanics 1999 Problem Set 5. Some useful data: water density = 1000 kg/m 3 viscosity of water = 0.0011 kg/ (m s) 1. Human aortas have a diameter of about 1 cm and the average speed of blood moving in these tubes is 20 cm/s. The average diameter of a human capillary is about 7 μ m in which there is an average blood flow velocity of about 0.07 cm/s. Use these data along with conservation of mass to calculate the number of capillaries contributing to blood flow in the system. 2. Because of the no-slip condition in a tube, there is a radial gradient in velocity. For simple flow in a straight tube, this gradient at the wall is du/dr = Δ P R / (2 μ L) where L is the length of the tube and R is the radius of the tube. A. Explain how there can be a gradient in velocity at the wall if the no-slip condition applies. B. Use Newton’s law of viscosity ( τ = μ du/dr) to compute the shear force (shear stress times the inside surface area) on a 10 cm long aorta under a pressure difference of 10

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## This note was uploaded on 06/03/2008 for the course BIOL 427 taught by Professor Daniels during the Spring '08 term at University of Washington.

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ps5 - Zoology 440 Biomechanics 1999 Problem Set 5. Some...

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