1. Feedback Loops
Friday, April 20th, 2018

2. Review: What are systems and how do they respond to change?
Open system: exchanges of matter and energy occur across boundaries
Closed system: No matter and energy exchanges across boundaries (occur way less)
Inputs: additions to a system
Outputs: losses from a system

3. System Analysis
Determine the inputs and outputs of a system and evaluate change
Steady state: when inputs = outputs so the system isn’t changing

4. Positive and Negative Feedback Loops
Positive: causes a system to change further in the same direction
Causes a system to change in the opposite direction; stabilizing
**** Positive is not necessarily “good,” negative is not necessarily “bad”

5. Positive Feedback Loop

6. Negative feedback loop
Negative feedback loop = output from a system moving in one direction acts as input
That moves the system in the other direction
Input and output neutralize one another
Stabilizes the system
Ex: predator – prey interactions
Most systems in nature

7. Positive feedback loop
Positive feedback loop = instead of stabilizing a system, it drives it further toward one extreme or another
Exponential growth in human population, erosion, melting sea ice
Rare in nature
But is common in natural systems altered by humans