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The Relationship between Variables.

The way that the
variables change

is called
the relationship between the
variables.

The relationship can be linear,

directly proportional, inversely proportional or non-linear.

Linear just means that the two
variables give a straight line
graph.

For example, the distance -
time graphs of a stationary object

and an object moving with constant
velocity are both linear.

Directly
proportional means that the rate of increase in one

variable is the same as the rate of increase in
the other variable.

If you double one thing, the other
thing doubles. For example,

the braking
distance of a car
is directly
proportional to its mass.

The resistance
of a wire is directly proportional to
its length.

Inversely
proportional means that the rate of increase

in one variable is the same as the rate of decrease

in
the other variable. If you double one thing, the other

thing halves. For example,
the resistance
of a wire is

inversely proportional to
the cross-sectional area of the wire.

Non-linear means that
the rate of increase in one variable

is not the same as the rate of
increase in the other variable.

For example, the braking
distance of a car

has a non-linear relationship to its velocity.

Enzyme
activity has a non-linear
relationship to temperature.

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