Variables are factors that might have some influence on an experiment

As an example, think of a simple experiment in which you are trying to determine the time it takes to toast a slice of bread. How long this takes will depend on many variables.

A few variables are:

• they type of bread (is it light and fluffy or heavy and dense?)
• The thickness of the slice (is thick, thin or in-between?)
• how dry the bread is (is it old, dry and stale or new, fresh and moist?)
• The make of the toaster (is it sunbeam, Breville or another brand?)
• The age of the toaster (is it new or old?)
• how clean the toaster is (is it clean or covered in crumbs?)

Independent variable

Once you have identified all the variables involved in an experiment, you then need to pick one to test. The variable you choose is known as the independent variable. It is the one you are going to change.

For the toast experiment, you might choose the thickness of the slice as your independent variable. You would change the thickness of the slice and test its effect on the cooking time.

Dependent variable

What you are trying to test and about to measure is known as the **dependent variable.**This is because it depends on the independent variable. Change the size of the independent variable and the size of the dependent variable is likely to change too. The dependent variable in the toast experiment is the time it takes to toast the slice-it depends on the thickness of the slice.

Controlled variables

Any experiment that you run needs to be a fair test. This means that only one variable should be changed at any time. All the other variables need to be controlled and held constant. For this reason, these variables are referred to as controlled variables. If they were changed too, then you would never know which variable caused changes in the experiment.

In the toast experiment, the controlled variables would be:

• the type of bread (choose one type of bread and use it throughout the experiment)
• how dry the bread is (all the bread you test would need to be the same dryness and age)
• the make, age and cleanliness of the toaster (stick with one toaster and don’t change it).

Ethical guidelines

• be safe

• be careful

• be honest

• be respectful

• take care of the environment

• take care of animals