Meeting 11 Universal Accounting Equation - Ijaz.pptx

# Meeting 11 Universal Accounting Equation - Ijaz.pptx -...

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Texas A&M University ENGR 112 – Spring 2018 Foundations of Engineering II Meeting 11 Universal Accounting Equation (UAE)

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Accounting When we hear the term accounting , most of us immediately think of money However, almost every engineering problem requires systematic tabulation of identifiable quantities (e.g., materials, time, money). This is also accounting The money part is just one example
System A system is a subset of the universe defined by an engineer for the solution of a problem. It is the part of the universe the engineer will model and monitor in order to evaluate some engineering process. Universe Surroundings System

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Choosing a System You are the engineer You have the privilege of choosing the system definition Choice based on the problem to be solved However, there are usually some choices that are better than others That’s when your engineering judgment will be called into play Holtzapple, Reece Foundations of Engineering
Rules for Systems You cannot change system definition during calculations This doesn’t mean the system quantities can’t change! System boundaries can be any shape but must be a closed surface System boundaries can be rigid to define a volume of space (a control volume ) or flexible to define an object

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Examples: Gas in a closed vessel (Tanks are nice control volumes; chemical engineers love them. So does Hank Hill.)
Examples: A beam with applied loads resting on rigid supports (statics is accounting!)

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Examples: The earth’s atmosphere (well-defined lower boundary, hard-to-define upper boundary, interesting geometry)
Examples: A transistor circuit subjected to a variable currents or voltages (Drawings of system are very important. Hard to tell what’s going on without them.)

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Examples: Hydraulic lift for a vehicle (How would you draw the system boundaries?)
Open and Closed Systems Closed systems : mass does not cross the boundaries of a closed system. Open systems : mass may or may not cross boundaries in an open system.

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Isolated and Non-Isolated Systems These are more restrictive than open and closed Isolated systems : neither mass nor energy nor momentum nor anything crosses the boundaries of a isolated system. (Nothing may cross.) Non-isolated systems : one or more of these may cross boundaries in an open system. (Something may cross.)
Homogeneous vs. Heterogeneous Systems

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