Definition:Definition: A system is a group of different A system is a group of different components that interact with each othercomponents that interact with each other

Distinguish: Distinguish: A system and A system and its external environment.its external environment.

A system is ….Its external environment is …

1.1. Isolated systemIsolated system no mass and no mass and energy exchangeenergy exchange

2.2. Closed systemClosed system no mass but no mass but energy exchangeenergy exchange

3.3. Open systemOpen system with mass and with mass and energy exchangeenergy exchange

There is no actual isolated system in There is no actual isolated system in the world.the world.

The universe can be considered as an The universe can be considered as an isolated systemisolated system

MassMass constant constantEnergyEnergy constant constantToward Toward maximum disorder maximum disorder die die

AtmosphereAtmosphere

OceanOcean

CryosphereCryosphere

BiosphereBiosphere

Earth SystemEarth System

External factor

SolarSolar

radiationradiation

Long-waveradiation

City

Identify the components

Determine the nature of the interactions between components

Systems Notation

= system component

= positive coupling

= negative coupling

Positive Coupling

AtmosphericCO2

Greenhouseeffect

• An increase in atmospheric CO2 causes a corresponding increase in the greenhouse effect, and thus in Earth’s surface temperature• Conversely, a decrease in atmospheric CO2

causes a decrease in the greenhouse effect

Negative Coupling

Earth’s albedo(reflectivity)

Earth’ssurface

temperature

• An increase in Earth’s albedo causes a corresponding decrease in the Earth’s surface temperature by reflecting more sunlight back to space• Or, a decrease in albedo causes an increase in surface temperature

Coupling: Component 1 Component 2

Positive same direction of changeincrease increasedecrease decrease

Negative opposite direction of changeincrease O decreasedecrease O increase

The interesting thing to do is to putcouplings together in feedback loops…

A Harmonious Family

childrens’noise

parents’ anger

positive coupling

negative coupling

NOT A Harmonious Family

childrens’noise

parents’ anger

positive coupling

positive coupling

The Harmonious/Non-Harmonious Family

Two possible states following perturbation:

1) Complete silence

2) Infinite noise

Positive feedback loop keeps a system unstable.

Negative feedback loop keeps a system stable.

A number of negative coupling

odd a negative feedback loop

even a positive feedback loop

Lisa’sbodytemperature

Lisa’sblankettemperature

Negative Feedback Loops:Electric Blankets

Mike’sblankettemperature

Mike’sbodytemperature

Lisa’s bodytemperature

Lisa’s blankettemperature

Mike’s blankettemperature

Mike’s bodytemperature

A Positive Feedback Loop:Mixed-up Electric Blankets

Any perturbation will cause both people to adjust their blanket controls, but with undesired consequences.

Ultimately, one person will freeze (become infinitely cold) and the other person to swelter (become infinitely hot).

Equilibrium State:

Conditions under which the system will remain indefinitely

--If left unperturbed

Stable?Stable?StableStable??