I believe that the project in question is
https://www.sciencebuddies.org/science- ... p016.shtml
The "Project" is written as a "demonstration of principles" that can be transformed into a Science Fair project. To utilize the scientific method to investigate something in order to make it a good Science Fair Project, you need to pick something specific that you want to test and then word it as your hypothesis.
Please read the "Getting Started" links on
https://www.sciencebuddies.org/science- ... ndex.shtml for "The Scientific Method"
https://www.sciencebuddies.org/science- ... thod.shtml and the links under "Constructing a Hypothesis".
The section on "Variables"
https://www.sciencebuddies.org/science- ... bles.shtml and "Variables for Beginners"
https://www.sciencebuddies.org/science- ... test.shtml describe what variables are in general.
In order to determine which "variables" are independent, dependent, and control, you need a "hypothesis"
https://www.sciencebuddies.org/science- ... esis.shtml. Your carefully worded hypothesis in a form similar to "if <this> then <that>" will provide the clues to what you are intentionally changing (THE variable associated with "<this>" is the independent variable - what you chose to intentionally change) and what you are measuring to determine "<that>" (dependent variable or variables). Everything else that you need to control in order to have a fair test are the controlled variables (control variables).
The difference between a "demonstration" and a great Science Fair Project is following the scientific method to investigate something which starts out as a statement of what you believe will happen and then coming up with an experiment to prove/disprove that involves a fair test.