mea chap 2

System

A set of connected things forming a complex whole

Models

A simplified representation of something

Characters of a system

Boundaries, Inputs & outputs, Cycles, Dynamic Interactions

Types of Systems

Isolated, Closed, Open

Isolated System

Does not exchange matter or energy with surroundings

Closed System

Exchanges energy but not matter with surroundings

Open System

Exchanges both matter and energy with surroundings

Cycle

A set of recurring events, returning to start regularly

Reservoirs

A place where the matter accumulates

Fluxes

Rate of transfer of matter from one reservoir to another

Residence time

the amount of time an average “piece” of matter (molecule or atom) resides in the reservoir

Residence time formula

Amount of matter in reservoir/Removal Rate or Supply Rate (only works if Removal=Supply. Steady State)

Sinks

Reservoirs with long residence times

Dynamic Interactions

Changes in one component of a system can affect other parts of the system

Couplings

Links between system components

Positive couplings

same direction of change in linked components

Negative couplings

Opposition direction of change in linked components

Feedback

when a change in one part of a system produces an effect that can further alter the first part of the system

Positive feedback

amplifies the initial change (snowballing)

Negative feedback

opposes the initial change (back to start)