Science fair problem. (Variables)

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Hello all,

I am at the start of a science fair project and have struck a problem. I was planning to test which Ph level would absorb a protein tablet the fastest. I am all good so far. I am in the planning stages of my project and I need to state what the independent and dependant variables are i will use. Problem encountered. What is the difference between a dependant and independent variable? What are some possible dependent and independent variables I could use in this experiment?
Thanx for your help,

Will :o