Topic 1
Systems and Models
What is a System?
• A system consists of:
– Storages
– Flows (inputs and outputs) (of energy or matter)
– Processes (trans...
storage
Energy or
matter in
(INPUT)
Energy or
matter out
(OUTPUT)
TRANSFORMATION
(Feedback mechanism to control input –
an...
Try to Produce a System Diagram
Ecosystems
• Most of the systems we will look at are
ecosystems (self contained communities of living
things and their sur...
Open, Closed and Isolated Ecosytems
• Open – matter and energy exchanged to
suroundings
• Closed – only energy exchanged t...
Biomes and Biospheres
• Biome – An open ecosystem in a
geographically defined area with similar
climatic conditions throug...
A Climograph
Meanannualtemperature(oC)
Rainfall (mm/year)
-15
-10
-5
-0
5
10
15
20
25
1000 2000 3000 4000 5000 6000
desert...
The Laws of Thermodynamics
• First Law – Energy can neither be created nor
destroyed, but can only be transformed
• Second...
Equilibrium
• A system needs to be in equilibrium
• If not, entropy will increase so much the
system will destroy itself b...
Static Equilibrium
time
State of the system
Note: this is not realistic – it could only
occur in an isolated system
Steady State Equilibrium
time
State of the system
Stable Equilibrium
time
State of the system
disturbance
Weebles
wobble but
they don’t fall
down!
Unstable Equilibrium
time
State of the system
disturbance
He’s going
down!
Feedback Mechanisms
• This is a way that the INPUT is affected by the
OUTPUT
• In a stable equilibrium, feedback returns t...
Negative Feedback
• Your (stable) equilibrium body temperature is
37oC
• Sensors in the skin detect your skin
temperature ...
Positive Feedback
• Your (stable) equilibrium body temperature is
37oC
• Sensors in the skin detect your skin
temperature ...
Case Studies
predator-prey equilibria
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Topic 1 – systems and models

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Topic 1 – systems and models

  1. 1. Topic 1 Systems and Models
  2. 2. What is a System? • A system consists of: – Storages – Flows (inputs and outputs) (of energy or matter) – Processes (transfer or transformation) – Feedback mechanisms (to maintain stability)
  3. 3. storage Energy or matter in (INPUT) Energy or matter out (OUTPUT) TRANSFORMATION (Feedback mechanism to control input – and maintain EQUILIBRIUM)
  4. 4. Try to Produce a System Diagram
  5. 5. Ecosystems • Most of the systems we will look at are ecosystems (self contained communities of living things and their surrounding environment) • Very large ecosystems which span a fairly stable climate are biomes • Many biologists say the whole planet is a single ecosystem (eg Gaia theory). Some of them call it a CLOSED ecosytem
  6. 6. Open, Closed and Isolated Ecosytems • Open – matter and energy exchanged to suroundings • Closed – only energy exchanged to surroundings • Isolated – neither matter nor energy is exchanged to surroundings • Is the Earth really a closed ecosystem? • Do isolated ecosystems really exist? • Can closed ecosystems be created artificially? (eg Biosphere 2 Project)
  7. 7. Biomes and Biospheres • Biome – An open ecosystem in a geographically defined area with similar climatic conditions throughout – eg, desert, grassland (savannah), tropical rainforest • Biosphere – A closed ecosytem – generally made up of a range of biomes (i.e. the entire Earth)
  8. 8. A Climograph Meanannualtemperature(oC) Rainfall (mm/year) -15 -10 -5 -0 5 10 15 20 25 1000 2000 3000 4000 5000 6000 desert grassland Tropical rainforest
  9. 9. The Laws of Thermodynamics • First Law – Energy can neither be created nor destroyed, but can only be transformed • Second Law – Energy is always changed from a concentrated (useful) form, to a dispersed (less useful) form – we say that ENTROPY (disorder) always increases (this means an isolated system cannot exist – there must be an input of energy to keep entropy low)
  10. 10. Equilibrium • A system needs to be in equilibrium • If not, entropy will increase so much the system will destroy itself by becoming too disordered • There a 4 kinds of equilibrium: – Static – Steady State – Stable – unstable
  11. 11. Static Equilibrium time State of the system Note: this is not realistic – it could only occur in an isolated system
  12. 12. Steady State Equilibrium time State of the system
  13. 13. Stable Equilibrium time State of the system disturbance Weebles wobble but they don’t fall down!
  14. 14. Unstable Equilibrium time State of the system disturbance He’s going down!
  15. 15. Feedback Mechanisms • This is a way that the INPUT is affected by the OUTPUT • In a stable equilibrium, feedback returns the equilibrium to its original state • In an unstable equilibrium, feedback returns the equilibrium to a different state • Feedback can be – POSITIVE – input changes to bring the system to a new equilibrium – NEGATIVE – input changes in order to bring the system back to its original equilibrium
  16. 16. Negative Feedback • Your (stable) equilibrium body temperature is 37oC • Sensors in the skin detect your skin temperature is rising (you are in Cancún) • Show what happens in a system diagram
  17. 17. Positive Feedback • Your (stable) equilibrium body temperature is 37oC • Sensors in the skin detect your skin temperature is decreasing (you are locked in a freezer) • Your body is unable to maintain its stable equibilibrium and therefore you enter a state of hypothermia • Show what happens in a system diagram
  18. 18. Case Studies predator-prey equilibria
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