Feedback - Simple English Wikipedia, the free encyclopedia

# Feedback

### From Simple English Wikipedia, the free encyclopedia

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Feedback is if the effect of a process (or things that come out of it) have a connection back to its cause (or things that go in to it).

For example: talk about this page. The process is communication, the thing that goes in is this page and the person who does the writing, and the thing that goes out (effect) is the comments.

## [edit] Feedback loops

In many situations output affects subsequent input and hence forms what is called a "feedback loop".

## [edit] Positive and negative loops

In some cases the output reinforces the input; this is typically called self-reinforcing or positive or runaway or amplifying.

In other cases the output cancels some of the input; this is typically called a negative feedback loop.

## [edit] Audio feedback

Consider a sound system with input from a microphone and output to a loudspeaker. If the sound coming from the loudspeaker is picked up by the microphone, a loop is created that, within a fraction of a second, creates a very loud noise.

This is an example of a positive feedback loop: the output reinforces the input.

## [edit] Flush toilet ballcock

Consider a water tank with an outlet and a float operated inlet valve. When water flows out it causes the float to sink, opening the inlet valve. When water flows in it causes the float to rise, closing the inlet valve.

This is an example of a negative feedback loop: the output (float rising) acts to reduce the input.

## [edit] The runaway global warming hypothesis

Consider how warmth melts a glacier. As the glacier melts, some portion of the area that had a heat reflecting snow/ice covering is now absorbent water or land, which in turn means the glacier melts faster than before.

There are actually many such feedback loops affecting the melting of glaciers, and other aspects of global temperature, some positive and some negative (some speeding up the warming, some slowing it down) but it's possible to sum all of these, at least in principle, and some scientists believe the net result of current global processes is a positive -- i.e. runaway -- feedback loop.

## [edit] Cybernetics

American mathematician Norbert Wiener popularized feedback loops in 1948 in his book "Cybernetics". Cybernetics is the study of feedback loops and their role in communication and control.

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