UCSB ENVS 106 - Lecture 09 Thinking in Systems Chapter 2_POST (24 pages)

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Lecture 09 Thinking in Systems Chapter 2_POST



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Chapter 2 A Brief Visit to the Systems Zoo Single Flow Single Stock Heat Inflow only Thermostat feedback leads to increasing heat inflow to the house When the setting is achieved heat inflow ceases A more powerful heater can increase the rate of heat inflow Note that the balancing feedback keeps the heater at 65 A more powerful heater does not serve much more of a function than simply heating up to 65 faster Single Flow Single Stock Heat Outflow only Outside feedback causes heat outflow from the house The larger the temperature difference the faster the outflow When the room cools down to the outside temp heat outflow ceases Better insulation can slow the rate of heat outflow Both Flows Single Stock Inflow and Outflow The strength of the heat inflow can override the heat outflow but it stabilizes at an average below the thermostat setting most people know you often need to set the heater a bit above the desired temperature Technically there s a subtle up anddown going on but it s easier to simplify the model and get rid of these minor balanced oscillations Dynamic Equilibriu m Achieved One Stock Systems System Model of a home heating system Pulling a single stock in two directions two flows Flow Dominance If one flow dominates another flow dynamic equilibrium is not achieved Why does the room temperature dip to nearly 53 F around hour 14 A The pressure of cold outside temperatures pulls the temperature down increasing heat outflow B The heat outflow is high due to poor insulation C The heat inflow is not high enough The reinforcing feedback of the birthrate dominates the balancing feedback of the death rate Balancing feedback of death rate dominates the low reinforcing feedback of the birthrate No Dominance The reinforcing feedback of birthrate and balancing feedback of death rate achieve dynamic equilibrium In the case of global population models fertility and mortality values change as countries are expected to develop and as specific diseases and other conditions affect a given geographical region These are what we call driving factors Three questions for testing the value of models such as population models 1 Are the driving factors likely to unfold this way 2 If they did would the system react this way 3 What is driving the driving factors A question of system boundaries Are driving factors themselves part of the system If so how might they feed back into the system Environment Economics Social Factors Population and Capital A population is nothing like an industrial economy except that both can reproduce themselves out of themselves and thus grow exponentially And both age and die A coffee cup cooling is like a warmed room cooling and like a radioactive substance decaying and like a population or industrial economy aging and dying Each declines as the result of a balancing feedback loop Response Delays Information delivered by the feedback loop can only affect future behavior There will always be delays in responding



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