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Systems and Models
Try thisThink of any system that is
cyclical and draw it as a model. For example, the seasons.
SystemAn assemblage of parts, working
together, forming a functioning whole.
May be small or largeMay be open, closed, or isolated
Take a minute and write down 3 examples of a system.
Examples of Systems
Ecological Other Types
PondBiomeAtmosphereOcean Island
SchoolPoliticalFamily
EcosystemA specific geographical area that takes
into account all biotic and abiotic factors that interact:
Ex: Biosphere = atmosphere (air) + lithosphere (rocks) + hydrosphere (water)+ ecosphere (life).
We look at howeach system interactsand not individual parts
Name a few factors that affect the interactions in this ecosystem
Open SystemsExchanges matter and energy
with its surroundings◦Any examples? ◦All ecosystems
Forests Marine Plains
◦You and your cells
ExampleForests Light enters the system
and plants fix energy during photosynthesis.
Topsoil may be removed by wind and rain
Mineral nutrients are leached out of soil and transported in groundwater to streams and rivers.
Water is lost through evaporation and transpiration.
To Do: using the model below, draw your own system for a cell phone.
Inputs
Flows
Storage
Flows
Outputs
Closed SystemExchanges energy but
not matter with the environment.
Extremely rare in nature
The Earth as a planet can be thought of as almost closed. Energy is exchanged in the form of visible light and infrared.
Very little matter gets in and out. Can you give examples?
Biosphere 2An attempt at a closed system. Never produced enough food to
sustain human participantsOften ran low on oxygen
Isolated SystemExchanges
neither matter nor energy with its environment
Do not exist naturally
It’s possible to think as the entire universe as and isolated system.
ReviewSystem Energy
ExchangedMatter Exchanged
Open
Closed
Isolated
Energy in Systems1st Law of Thermodynamics: Energy is
neither created nor destroyed. Energy can change from one form to another
(light to heat) but no new energy is created. Sometimes called conservation of energy.
In a food chain: Light is changed to chemical energythrough photosynthesis and transferred again as chemicalenergy to an herbivore and then carnivore.
1st Law ContinuedWhat about sunlight? What
happens to all of the light that reaches Earth?
30% reflected back into space50% converted to heat19% powers hydrologic cycle1% used for photosynthesisThat’s 100%
2nd Law of ThermodymicsWhen energy is transformed into
work, some energy is always lost as waste heat.
Energy = work + heat◦Can you give an example of this law
that you may experience often?◦Car engine: Does work but gets very
hot. Engineers would love to create an engine that doesn’t lose energy as heat. Think how fast you could go!
2nd Law Continued: Does the lion get as much energy from the plant as the herbivore?
Energy Efficiency
EquilibriumTendency of a system to return to an original
state following disturbance. ◦ A rubber band can be stretched but it will always
return to its original shape. Open systems tend to exist in a state of
equilibrium. Stable Equilibrium: System returns to same
equilibrium after disturbanceSteady-State Equilibrium: No change over the
long term but small changes over the short term.
Unstable Equilibrium: System returns to a NEW equilibrium after disturbance. (Climate?)
Ecosystem EquilibriumUnstable Equilibrium
Stable Equilibrium
Tipping PointThe minimum amount of change
within a system that will destabilize it, causing it to reach a new equilibrium or stable state.◦Can you think of any human impacts
on the environment that might lead to a tipping point?
Positive and Negative FeedbackMost systems are
affected by feedback- the processes, energy, or matter that change the system.
Positive Feedback: Encourages a change
Negative Feedback: Discourages further change
Positive Feedback Negative Feedback
Causes a system to change further.
Example: Climate Change
Causes as system to change in opposite direction it is moving or causes it to slow down.
Ex. Thermostat
To Do: On Page 82-83 of the Course
Companion, complete the Review.
Label each example as positive or negative feedback.
Draw diagrams of one example of positive feedback and one example of negative feedback. Include feedback loops in your diagram.
Models of systemsModels of a system predict changes
◦Physical Models: Wind tunnel, globe, solar system, aquarium
◦Software Models: Climate change, population dynamics, groundwater flow
◦Mathematical equations◦Data flow diagrams
Limitations: ◦may lack some complexities of real
world◦Rely on available data
In this class we will…Model climate and climate
changeModel human and species
population dynamicsModel groundwater flowModel different types of energiesModel landfills and pollution
clean up And others
Climate Model Inputs
Population Growth Model
Groundwater Flow Model
032
6496
128160
192224
256288
0.000
2.000
4.000
6.000
8.000
10.000
12.000
14.000
100
50
0
-50
-100
(ft)
Co
nce
ntr
atio
n (
mg
/L)
(ft)
To Do: 1.) Daisyworld Modeling:
http://ccl.northwestern.edu/netlogo/models/Daisyworld
2.) Climate Modeling: Using Netlogo, open the climate model and follow instructions.
Models of Systems Activity (Handout)