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)