# What is a System?

Mechanics

Oct 27, 2013 (4 years and 6 months ago)

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What is a System?

A
system

is a set of interacting or interdependent
components forming an
integrated whole.

S
ystems
share common characteristics, including
:

A system has
structure
, it contains parts
that
are
directly or indirectly related to each
other

A system has
behavior
, it contains processes that
transform inputs into
outputs

A system has
interconnectivity
: the parts and
processes are
connected.

SYSTEMS

Examples of systems
:

Ecosystems, weather systems, food
production systems, sewage treatment
systems, photosynthesis, education systems,
information distribution systems, your
body………

All systems have
:

Inputs

energy or materials or both

Outputs

energy, materials or both

may be useful

ex.
a crop

may be a problem

ex.
pollution

When a system is in
equilibrium:

inputs = outputs

Ex.
The
temperature of our planet will
remain constant, provided
that

energy
inputs = energy outputs.

If we reduce the outputs of energy by
increasing levels of greenhouse gases which
trap heat energy, the temperature rises (global
warming).

There are
3 main types of systems
:

System type

Energy

Materials

Examples

open

Inputs and outputs

Inputs and outputs

Most common type
of system
-

includes
most ecosystems,
food production
systems and many
others

closed

Inputs and outputs

NO inputs or
outputs, cycle
within system

The Earth is
almost

a closed system;
aquarium with
sealed lid;
biosphere domes

isolated

No inputs or
outputs

No inputs or
outputs

An abstract concept
-
difficult to find real
life examples

possibly the
universe is an
example

Systems and the Laws of
Thermodynamics

The
First Law of Thermodynamics

tells us
:

“Energy is never created or destroyed, only
changed from one form to another”

Think of a food chain……

Systems and the Laws of
Thermodynamics

The
Second Law of Thermodynamics
tells us
that
a
ll
energy changes release some energy
as heat, and eventually all the energy in the
universe will have turned to low grade heat
energy.

A very happy thought…

Again think of a food chain……

Feedback mechanisms in
systems

feedback

occurs when the output of a system
influences the inputs and hence affects the
state of the system

positive feedback

changes a system to
a new
state
. In most natural systems it is considered
but it is
not

always so! The term
“vicious cycle” usually refers to positive
feedback.

Positive Feedback examples

-
Ex
.
A common example occurs during conferences
when a microphone gets too much sound from a
speaker. The speaker sound is amplified, resulting
in even more speaker sound to the microphone.
The sound level quickly increases in volume,
eventually overdriving the amplifier, resulting in
that awful squeal we all hate
.

-
Ex
. teacher encourages student with positive feedback
comments on his/her work; student associates learning
higher standard of work (a new state!). Student gains
confidence from achievement, passes exams and leaves for
university.

Feedback mechanisms in systems

negative feedback
returns a system to its

original state
. In many natural systems
homeostasis
acts as a form of negative
feedback

.
In most natural systems
,
negative
feedback is considered
a good thing
, because
it restores
state.

Negative Feedback Examples

-

Ex
.
As the number of rabbits increases in a natural
area, there is more food for predators, resulting in
an increase in the number of predators. This
increase causes a decrease in the number of
rabbits, resulting in fewer predators. The result is
that the ratio of rabbits to predators is nearly
constant.