The weight of a projectile doesn't affect its air resistance. The drag force D acting on an object with a reference area travelling with a velocity V is given by

where is the density of the medium (1.225 kg/m3 for air) and is a dimensionless quantity known as the drag coefficient, which is a value that describes how much drag acts on the body. Various drag coefficients of objects are listed here: https://en.wikipedia.org/wiki/Drag_coefficient. However, as noted in the Wiki article, the drag coefficient itself is not constant, and is a function of a dimensionless quantity known as the Reynold's number (which itself is a function of a few other flow variables, velocity being one of them). These drag coefficient values are determined experimentally using wind tunnel testing, so that could be a possible topic: The effect of the Reynold's number on the drag coefficient of a sphere (or some other object). Note that physics is quantitative in nature, so having equations and such to throw around is always good. Also, fluid dynamics is still a very active and complex area of research and is heavily based on experiments using wind tunnel testing, so you'll be able to find an abundant amount of information on this. Most of it will likely be too complicated for even your teachers, but you should be able to find resources that contain graphical results of experiments which should be relatively straightforward to use.

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