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 Know the Universal Accounting Equation and how to use to solve problems.
 Explain what a system is and give examples.
 Describe intensive and extensive quantities.
 Know the rules concerning the study of a system.
 Distinguish between state quantities and path quantities.

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 Yes, Accounting is a very important component of Engineering.
 Each Engineering discipline has its own accounting specialties (see
Table 17.1).
 Proper accounting is essential to organized thought.
 Therefore, we must define the system, that part of the Universe we wish
to study.

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 The surroundings are everything in the Universe except the System.

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 Everything that exists is called the Universe.
 A system is one component of the Universe. It can be a factory, a
school, a laboratory, the solar system, or a molecule. It is what you
choose to investigate.
 There are certain rules an engineer must follow in the study of a
system.

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 1. Once a System is specified, it
cannot be changed midway through a calculation.
 2. The System boundary can be any
shape, but it must be a closed surface.
 3. The system boundary can be
rigid, thus defining a volume of space; or it can be flexible, thus
defining an object.

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 Spacetime coordinates are needed to define the system.
 The spatial coordinates describe where the system exists and the time
coordinates describe when the system exists. Since systems usually
change over time, the system can be described using time t_{1}
and later at a time t_{2}.

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 Review the 5 possible systems for analyzing a hydraulic lift in Figure
17.3 in your text.
 An engineer might want answers to these questions:
 What pressure is required to lift the automobile?
 How much work does the pump do when lifting?
 What volume of hydraulic fluid must be pumped to lift the automobile a
given height?

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 Extensive quantities change as the system changes, but intensive
quantities do not.
 Extensive quantities (e.g., mass, moles, volume) can be counted but
intensive quantities cannot (e.g., color, temperature, pressure).
 The following rules apply to intensive and extensive quantities.

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 4. The ratio of two extensive quantities is intensive. For example, D =
m/v.
 5. An equation with an extensive quantity on the left side must also
have an extensive quantity on the right side. Example: PV=nRT. V and n
are extensive quantities.

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 6. The extensive form of an equation can be transformed into an
intensive form by dividing both sides by an extensive variable. For
example, the ideal gas law can be transformed by dividing each side of
the equation by n which gives PV^{*} = RT ( the intensive
form). Where V^{* }= V/n
is the specific volume. (See Table 17.2 in your text for examples of
specific quantities).

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 Are formed by dividing an extensive quantity by mass or moles.
 An extensive quantity results when the specific quantity is multiplied
by mass or moles.

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 State quantities are independent of path and path quantities are
dependent on path.
 Suppose you wish to travel from Virginia to California. You could choose a
northern route or a southern route or a more direct route.
 See the map on the next slide.

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 The distance traveled depends upon the path taken, with path A requiring
the shortest distance.
 The state we occupy, however, does not depend on the path taken, so it
is a state quantity.
 The following rules pertain to state and path quantities.

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 7. Extensive state quantities are contained within the system boundary,
whereas extensive path quantities pass through the system boundary and
have the ability to change the state of system.
 Example: Consider a beaker
 1/3 full of water

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 The water volume in the system (extensive state quantity) is changed by
adding or draining water volume (extensive path quantities).
 8. Algebraic combinations of state quantities are also state quantities.
Example; Specific enthalpy H, which is defined as the sum of specific
internal energy U and PV. H = U +
PV
 Because U, P, and V are all state quantities, then H must also be a
state quantity.

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 9. Algebraic combinations of state quantities and welldefined path
quantities are state quantities. Consider a beaker with a volume of
water at initial height h_{1}.

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 The initial height h_{1} and cross sectional area A are both state quantities. They are algebraically combined with
the path quantity V_{no drainage } to give the state quantity h_{2}.
Notice that the path quantity V_{no drainage } must be well defined by specifying that
there is no drainage. This careful description is necessary for the
equation in the last slide to be valid.

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 1. Spacetime coordinates can be
used to define system boundaries.
 2. State quantities define the
system contents.
 3. Path quantities define things
that affect the system by passing through the system boundary.
 See Table 16.3 for a summary of the classification scheme and some
examples.

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 Process 1 > 2 is an isothermal expansion in which the the gas is
placed in thermal contact with a heat reservoir. The gas absorbs heat
from the reservoir and does work in raising the piston.
 In the Process 2 > 3, the gas expands adibatically, the temperature
drops and the gas does work in raising the temperature.

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 In the process 3 > 4, the gas is placed in thermal contact with a
heat reservoir and is compressed
isothermally. During this time, the gas expels heat to the reservoir,
and work is done on gas.
 In the final stage, 4 > 1, the gas is compressed adiabatically the
temperature of the gas increases and work is done on the gas.
 Path quantities( i.e., heat and work) were able to effect a change in
state properties.

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 The following classifications schemes are used to classify systems:
 Closed and Open
 Isolated and Nonisolated
 Homogeneous and Heterogeneous
 Steady State and Unsteady State

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 An open system is one in which mass DOES cross the boundary and a closed
system is one in which mass DOES NOT cross the boundary.
 An example of a closed system is a light bulb; an open system example is
an automobile engine.

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 If mass enters a system so do properties associated with mass (specific
volume, specific enthalpy, specific internal energy) at some m_{in}.
 When mass flows out of the system the properties mentioned above flow
out at m_{out}.
 In other words, a balance is maintained.
 See Table 17.4 for property analysis.

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 An isolated system has nothing crossing the boundary; no mass, no
charge, no linear momentum, no angular momentum, and no energy. The
universe is the only truly isolated system. Why?
 Many systems that engineers study closely approximate isolated systems.
 A nonisolated system has at least one of quantities mentioned above
crossing the boundary.

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 A homogeneous system has the same properties throughout, whereas a
heterogeneous system has different properties throughout.

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 A steadystate system does not change with respect to time, but an
unsteadysystem does. Consider a swimming pool:

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 This equation is an axiom, that forms the foundation of rational thought
in most engineering disciplines. It requires that the engineer do the
following:
 Identify the system to be investigated.
 Determine what will be counted.
 Define a time interval during which the counting will be carried out.

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 Final Amount – Initial Amount = Input –Output + Generation – Consumption
 The left side of the equation accounts for all state quantities and the
right side accounts for all path quantities.
 Exact definitions for each component of the are necessary.

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 Final Amount Specifies the amount of the counted quantity in the system
at the end of the time period.
 Initial Amount Specifies the amount of the counted quantity in the
system at the beginning of the time period.
 Input Specifies the amount of the counted quantity passing through the
system boundary into the system during the time interval.

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 Output Specifies the amount of the counted quantity passing through the
system boundary out of the system during the time interval.
 Generation Specifies the amount of the counted quantity produced during
the time interval within the system boundary.
 Consumption Specifies the amount of the counted quantity destroyed
during the time interval within the system boundary.

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 Accumulation = Net Input + Net Generation
 The left side of the equation describes the change in state caused by
the path quantities on the right side of the equation.
 Problem: A chicken coup starts the year with 34,000 chickens. During the
year, 16,000 chicks are purchased, 20,000 chickens are sold, 12,000 eggs
hatch, and 20 chickens are eaten by foxes. How many chickens are present
at the end of the year? (See Figure 17.12)

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 Final Amount – Initial Amount = Input –Output + Generation – Consumption
 34,000 + 16,000 –20,000 + 12,000 –20 = 41,980 chickens

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 A system is at steady state when there is no accumulation. Therefore,
the universal accounting equation becomes:
 0 = (input – output) + (generation – consumption) or
 0 = Net input + Net generation

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 Many engineering quantities (such as mass, charge, momentum, energy) are
conserved.
 For these quantities, the universal accounting equation reduces to:
 Final Amount – Initial Amount = (Input – Output) or Accumulation = Net
Input.
 For a system at steady state and with conserved quantities, the equation
reduces to 0 = Net Input.

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