New Physics for You, pages 7 and 360 How Science works: Variables New Physics for You, pages 7 and 360

Learning Objectives You should learn : About the different types of variables, How to identify them when doing your practical work.

Variables are things that vary and change

Variables In any experiment there are 3 variables: an independent (or input) variable a dependent (or outcome) variable some constant (or control) variables Let’s look at each type….

Independent (Manipulated) variable This is the thing that you decide to change. There should only be one at a time. Example 1 Investigating how a weight affects the length of an elastic band. You decide the weight to apply, so: Weight is the independent variable.

Independent (manipulated) variable This is the thing that you decide to change. Example 2 Investigating if a fertilizer will make beans grow better than just normal soil. You decide to give the plants fertilizer, So the fertilizer is the independent variable.

Dependent (Responding) variable This is the variable that changes as a result. It is the variable that you measure. Example 1 Investigating how a weight affects the length of an elastic band. You measure the resulting length of the elastic band, so: Length is the dependent variable.

Dependent (responding) variable This is the variable that changes as a result. It is the variable that you measure. Example 2 Investigating if a fertilizer will make beans grow better than just normal soil. You measure the growth of the bean plant, so: Plant growth is the dependent variable.

Constant (control) variables These are all the variables that must not change, to make sure it is a fair test. Example 1 Investigating how a weight affects the length of an elastic band. You must use the same elastic band all the time, and the same scale etc, so it is a fair test.

Constant (Control) variables These are all the variables that must not change, to make sure it is a fair test. Example 2 Investigating if a fertilizer will make beans grow better than just normal soil. You must use the same kind of beans, with the same amount of water, in the same amount of sunlight, at the same kind of soil, so it is a fair test.

same elastic band, same scale, etc, so it is a fair test. In Summary Example 1 The independent variable is ? weight The dependent variable is ? length of the elastic The control variables are ? same elastic band, same scale, etc, so it is a fair test.

In Summary the fertilizer the growth of the plant Example 2 The independent variable is ? the fertilizer The dependent variable is ? the growth of the plant The constant variables are ? the same kind of beans, with the same amount of water, in the same amount of sunlight, at the same kind of soil, so it is a fair test.

Test Group The group in the experiment that receives the independent variable Their results tell you if the independent variable makes a difference

Control Group The group in the experiment that doesn’t receive the independent variable Their results tell you what would happen normally. It gives you something to compare your test data to.

Placebo Effect When people in the control group get better because they think they are being treated.