Its been awhile since I even thought about conducting a scientific experiment, and I do remember that you need a dependent variable.. the observation or effect such as the apple fell from the tree, and then the independent variable, such as gravity. But in order to test the hypothesis, you need to alter the independent variable. (a cause) (and there can only be 2 independent variables). How could you effectively alter gravity? or would you alter its effects by testing its effects through a known resistance or medium and then make changes to that... or would you simulate its force to create similar effects and then change the force .