Our Changing Planet Ch 2
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is an entity composed of diverse but interelated parts that function as a complex whole.
- are the individual parts of the system.
- examples: resevoir of matter, energy, or an attribute of a system(such as body temp. or pressure), or subsystem (such as cardiovascular)
- of a system is the set of important attributes that characterize the system at a particular time.
- ex: body temp., level of nutrition, and blood pressure are among the attributes that determine the state of a human body.
- clear from examples of the human body it is clear that the components of the human body "system" do not exist in isolation; they are linked, allowing for flow of information to go from one component to the next.
- these links are couplings
- ex: in the elctric blanket example, an increase in blanket temperature causes an increase in body temp; this is called positive coupling
- a change (increase or decrease) in one component leads to a change of the same direction in the linked component.
- ex: in contrast an increase in body temp. above conmfort level would lead you to decrease the amount of heat by turning down the controller.
- a change in one component leads to a change of the opposite direction in the linked component. (ie if increases then other component decreases, and reverse)
- feedback is a self-perpetuation mechanism of change and response to that change.
- ex: consider Deb who is boss of Ed. If Deb complains that Ed is dressing innapropriately at work, Ed may respond by dressing more consevatively, or 2 other outcomes dressing more innapropritely or the same. Either reaction (now an action) will undoubtedly cuase a subsequent reaction--praise or criticism--from Deb.
negative feedback loop
- negative feedback loops tend to diminish the effects of disturbances.
- ex: an increase in body temp., caused you to turn down controller on blanket, the blanket radiates less heat, and your body temperature then decreases.
positive feedback loops
- amplify the effects of disturbances
- ex: President Jimmy Carter and his Wife; "Whenever I said it was too warm, Rosalynn said it was too cold, and vice versa." There remotes were switched, so when one became cold they would turn up the heat but since it was directed from there partner, then there partner would be getting to hot so would make it colder then again controlling not theirs but their partners
difference bt Negative and Positive Feedback Loops?
- count number of negative couplings.
- Negative feedback loops have an odd number of negative couplings; multiplication apply hear. 2 (+) numbers multiplied = (+) but also two (-) numbers multiplied is (+) only time negative is a (+) x a (-).
- ex: if your body temperature is just right and comfortable range you do nothing to the blanket controller.
- it will not change unless the system is disturbed
- because this state is created by a negative feedback loop, the equilibrium state is said to be stable
- ex: modest disturbances from this state will be followed by system responses that tend to return the system to its equilibrium state
the slightest disturbance from a comforable state led to system adjustments that carried the system further and further from that state
- or temporary disturbance of a system
- ex: injection of sulfur dioxide into the atmosphere during the 1991 volcanic eruption of Mt. Pinatubo in the philippines
a more persistent disturbance of a sysstem
- the reflectivity of a surface
- ususally expressed as a decimal fraction of the total incoming incident
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