1. Lesson /5/18
SWBAT identify and model the elements of a feedback system Do Now: Which greenhouse gas is the most abundant? Which greenhouse gas is released due to the combustion of fossil fuels? Which greenhouse gas is released due to livestock?

2. Systems Systems receive inputs and produce outputs.
Systems: A network of relationships among parts that interact with one another.
Exchange energy, matter or information.
Systems receive inputs and produce outputs.

3. System

4. Feedback Loops
When an event is both an input (cause) and output (effect).
Results in a cycle
Can be either negative or positive.

5. Negative Feedback Loops
A change (increase or decrease) in one variable leads to an opposite change in the second variable in order to maintain balance
Common in nature
Ex: thermostat

6. Negative Feedback Loops
Promotes stability

7. Examples: Negative Feedback Loops
Blood sugar and glucose
Thermostat

8. Positive Feedback Loops
A change (increase or decrease) in one variable promotes the same kind of change in another variable
Amplifies intensity
Generally rare, but common in environments changed by humans.
Ex: poison ivy

9. Positive Feedback Loops
Unstable

10. Example: Positive Feedback Loop
Poison Ivy
Itches skin, you scratch, it itches more, so you scratch more…

11. Positive vs. Negative feedback loops

12. Example: Positive or negative?

13. Example: Positive or negative?

14. Positive or Negative Feedback Loop?

15. Modeling feedback loops
Step 1: Underline what changes in the paragraph
Step 2: Fill in the boxes with what changes

16. Video

17. Exit Ticket
1. Which feedback loop is more stable: positive or negative? 2. Which one is more commonly found in nature? Why?

18. Homework
Research an example of positive and negative feedback loops. List your source.