Feedbacks_F10_Lect7

Feedbacks_F10_Lect7 - Feedbacks Fall 2010, Lecture 7 1...

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Feedbacks Fall 2010, Lecture 7 1
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Feedback Mechanism Any process that acts to oppose or amplify changes to a system that is in a steady state Feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input The response is often proportional o That is, as the system deviates more from the steady state position, the faster the process works to counteract it. 2
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3 Homeostasis Property of an open system, especially living organisms, to regulate its internal environment so as to maintain a stable condition, by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms Term was coined in 1932 by Walter Cannon from the Greek roots homo- (same, like) and sta- (to stand or stay)
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4 Negative Feedback A type of feedback, during which a system responds so as to reverse the direction of change Since this process tends to keep things constant, it is stabilizing and attempts to maintain homeostasis
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5 Negative Feedback Example - A ball Rolling Inside a Curved Bowl Initially, the ball oscillated from side-to-side, rising far up the sides of the bowl With time, the amplitude of the motion decreases until the ball comes to rest at the bottom of the bowl Once stationary, the ball has reached a position of stability
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6 Positive Feedback – Microphone Screech Small sounds picked up by the microphone are amplified by the nearby speaker, where the microphone once again picks up the amplified sound and rebroadcasts it through the speakers This looping continues until the initially tiny sound is re- amplified repeatedly to a piercing squeal
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Audio Feedback An example of microphone-speaker feedback 7
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8 Nuclear Chain Reaction
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9 Cybernetic Systems From the Greek kubernetes , meaning a steersman Cybernetics means the branch of study concerned with self-regulating systems using communication and control in either mechanical devices or living biological organisms
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10 Cynernetics at Work -Walking Babies need to learn to control their balance
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11 Cybernetic System Components Sensor Amplifier Controller
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12 Instrument vs. Man Cybernetic control by electrical system   Cybernetic control by human brain
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Feedback Terminology State variable – the quantity that is being fed- back Feedback loop – the loop of causality Input perturbation – any disturbance to the system 13
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Climate Feedback Loops Ice Albedo Stefan-Boltzmann Water Vapor Hydrologic Cycle 14
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Ice Albedo Feedback Ice with snow cover has a high albedo of about 0.9, meaning that 90% of incident radiation is reflected into space – there is little heating of the ground Bare ice absorbs about 50% of the incident radiation Open ocean absorbs 94% As ice melts, more and more heat is retained, creating a positive feedback 15
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Ice Melting with Albedo Change Animation illustrates the effect of albedo change 16
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How climatologists have fun…. . 17
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Feedbacks_F10_Lect7 - Feedbacks Fall 2010, Lecture 7 1...

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