Variables are things that you can vary, or that can vary outside of your control. Specifically:
Dependent Variable: this is the thing that will change depending on other things. For example the extension or length of the spring. These both depend on how much mass is added, for example.
Independent Variable: this is the thing that you will be changing, to see its effect on the dependent variable. e.g. the mass added.
Control Variables: these are the independent variables that you identified in P6a that may affect the dependent variable - but you choose NOT to alter them as you are NOT investigating them! Instead you MUST make sure they don't change - if at all possible.
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