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How Science Works

Variables - Independent - Dependent.

The variable which is chosen for an investigation by the
person doing the experiments is called the independent variable.
The thing being affected is called the dependent variable.

For example, the rate of the reaction between hydrochloric acid
and calcium carbonate can be measured by
looking at the rate of production of carbon dioxide gas.

If we look at how the temperature of the hydrochloric acid
affects the rate of carbon dioxide production,
then temperature is the independent variable and the
rate of carbon dioxide production is the dependent variable.

If we look at how the concentration of the hydrochloric acid
affects the rate of carbon dioxide production,
then concentration is the independent variable and the
rate of carbon dioxide production is the dependent variable.

It is important to choose values of the variables which
are appropriate for the experiment. The first experiment
will be a trial run which will tell you the quantities that
you need (for example the amount of hydrochloric acid
and calcium carbonate) and the appropriate conditions
(for example the temperature range or concentration range).

A plot (graph) of the results will often show a more
interesting region where a pattern is changing quickly.
It will be necessary to repeat the experiment with
measurements closer together to show
more detail in a region where a pattern is changing quickly.

The independent variable is plotted on the X axis of a graph.

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