Systems and Feedback Loops

1
Systems and Feedback Loops
2
Questions for Today

• What is a system and its parts?
• What are the different types of system response?
• What is a time delay?
• What is synergy and how is it harmful and
  beneficial?

3
Parts of a System

• A system is a set of components that function and
  interact in some regular way.
• Parts of a system
• Inputs
• Flows or thoroughputs
• Outputs
• Environmental scienctists use computer modeling
  to analyze systems.

4
Throughputs
Outputs
Energy Inputs
Energy resources
Heat
Matter resources
Waste and pollution
Economy
Goods and services
Information
Fig. 2-10, p. 44
5
Feedback Loops

• Systems respond to change through the use of
  feedback loops
• Two types of feedback loops
• Positive process that increases change
• Negative - process that decreases change
• Homeostasis

6
Positive Feedback Loops

• A feedback loop occurs when an output of matter,
  energy, or information, is fed back into the
  system as an input and leads to changes in that
  system.
• A positive feedback loops causes a system to
  change further in the same direction.
• Examples of Harmful Feedback loops
• Deforestation
• Melting of Polar Ice Caps
• Examples of Beneficial Feedback Loops
• Blood Clotting
• Ecological Succession

7
Decreasing vegetation...
...which causes more vegetation to die.
...leads to erosion and nutrient loss...
Fig. 2-11, p. 45
8
Negative Feedback Loops

• Negative, or corrective, feedback loops causes a
  system to change in the opposite direction from
  which it is moving.
• Examples
• Thermostat
• Recycling

9
House warms
Temperature reaches desired setting and furnace
goes off
Furnace on
House cools
Temperature drops below desired setting and
furnace goes on
Fig. 2-12, p. 45
10
Time Delays

• Time Delays are a gap in time between the input
  of a feedback stimulus and the response to it.
• The results of deforestation or pollutants
  usually have a time delay before the system
  reaches a threshold, or tipping point, where the
  damage is irreversible.

11
Synergy

• Synergy is when two or more process interact so
  that the combined effects are greater than the
  sum of their separate effects.
• Harmful Example
• Smoking and Asbestos leading to Lung Cancer
• Air Pollutant Cocktails
• Beneficial Example
• Writing your Congressmen (Cheesy, Huh?)