Extensions

Students could compare results with two populations, say some doing "sharp" rocks - where perhaps the sharpness in the hand may lead to the perception the rock is "heavier" and others doing "smooth" rocks.

Comparisons might be done with heavier masses, e.g., use 1 kilogram as the standard mass.

Refinements could be done on other variables, e.g., class - soph, jr, sr., etc., major, "dorm," home state, etc.