Fluid ch01

# Fluid ch01 - Problem 1.1 1.1 Tar `Silly Putty Modeling clay...

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Problem 1.1 [ 3 ] 1.1 A number of common substances are Tar Sand ‘‘Silly Putty’’ Jello Modeling clay Toothpaste Wax Shaving cream Some of these materials exhibit characteristics of both solid and fluid behavior under different conditions. Explain and give examples. Given: Common Substances Tar Sand “Silly Putty” Jello Modeling clay Toothpaste Wax Shaving cream Some of these substances exhibit characteristics of solids and fluids under different conditions. Find: Explain and give examples. Solution: Tar, Wax, and Jello behave as solids at room temperature or below at ordinary pressures. At high pressures or over long periods, they exhibit fluid characteristics. At higher temperatures, all three liquefy and become viscous fluids. Modeling clay and silly putty show fluid behavior when sheared slowly. However, they fracture under suddenly applied stress, which is a characteristic of solids. Toothpaste behaves as a solid when at rest in the tube. When the tube is squeezed hard, toothpaste “flows” out the spout, showing fluid behavior. Shaving cream behaves similarly. Sand acts solid when in repose (a sand “pile”). However, it “flows” from a spout or down a steep incline.

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Problem 1.2 [ 2 ] 1.2 Give a word statement of each of the five basic conservation laws stated in Section 1-4, as they apply to a system. Given: Five basic conservation laws stated in Section 1-4. Write: A word statement of each, as they apply to a system. Solution: Assume that laws are to be written for a system . a. Conservation of mass — The mass of a system is constant by definition. b. Newton's second law of motion — The net force acting on a system is directly proportional to the product of the system mass times its acceleration. c. First law of thermodynamics — The change in stored energy of a system equals the net energy added to the system as heat and work. d. Second law of thermodynamics — The entropy of any isolated system cannot decrease during any process between equilibrium states. e. Principle of angular momentum — The net torque acting on a system is equal to the rate of change of angular momentum of the system.
Problem 1.3 [ 3 ] 1.3 Discuss the physics of skipping a stone across the water surface of a lake. Compare these mechanisms with a stone as it bounces after being thrown along a roadway. Open-Ended Problem Statement: Consider the physics of “skipping” a stone across the water surface of a lake. Compare these mechanisms with a stone as it bounces after being thrown along a roadway. Discussion: Observation and experience suggest two behaviors when a stone is thrown along a water surface: 1. If the angle between the path of the stone and the water surface is steep the stone may penetrate the water surface. Some momentum of the stone will be converted to momentum of the water in the resulting splash.

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## This note was uploaded on 09/08/2010 for the course AME 331 taught by Professor Zohar during the Spring '08 term at Arizona.

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Fluid ch01 - Problem 1.1 1.1 Tar `Silly Putty Modeling clay...

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