Why are variables important in a science investigation?

I got this from bcps.org.

The procedure used in an experiment must be written in a clear, sequential manner

in order to allow someone else to follow the same steps to replicate the experiment.

Numbering the steps followed in the procedure is helpful to someone who is reading

the procedure. In determining the procedure that will be used in the investigation

the factors that will affect the outcome of the experiment, called variables, must

be identified and controlled. There are three types of variables that must be

considered:

• Independent variable (manipulated variable) - the factor that will be

intentionally changed during the experimental procedure in order to find out what

effect it has on something else. An example of an independent variable is using

different lengths of string to construct a pendulum in order to observe the effect

the length of the string has on the swing of the pendulum.

• Dependent variable (responding variable) - the factor that is observed and

measured to see if it is affected by the change made in the independent variable.

An example of a dependent variable is the number of swings the pendulum makes

when the length of its string is changed.

• Variables that are controlled - the factors in the experiment that must be kept

exactly the same to make sure that they are not having any effect on the dependent

variable. Variables that would need to be controlled in the pendulum experiment would

be the mass of the pendulum, the type of string, and the release height of the pendulum.

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Great copying job!

Now we know what they are.

But why are they important ? ! ?

The question still needs an answer.