Hi Forum. So I'm doing a physics experiment where I drop marbles in different viscous liquids and I am suppose to discuss the relationship of the marble's velocity. But I am changing the marble's diameter and mass at the same time since I don't have any marbles which have the same mass but different radius and vis versa. So now i can't come up with a reasonable researchable question. Will this work? The relationship of the velocity when the density of the marble is changed. Or, since i am just scaling the marbles up, i can assume that the mass is negligible or something? Now the second bit of my problem. Since both variable contribute to the change in velocity, I don't understand entirely why my results are this. My experiment - I am keeping the volume of the liquid constant but changing the viscosity of the liquids. The marbles mass and volume are increasing successively, i.e. those ordinary small sized marble and then a bigger mass and bigger volume. It is dropped in the liquid and timed how long it takes to reach the bottom. My data shows that the bigger marbles takes longer to fall through the liquid. It seems reasonable since there is less room to flow past the marble and that the velocity of the liquid near the sides are slower which would in turn slow down the velocity of the flowing liquid? (dunno whether i am right 'bout the second reason) But the increasing weight more drag is required to slow down the marble. So how can I explain why its all happening the way its happening when I'm changing two variables at the same time. As I can't model one variable and its result. Also I tried to keep the mass constant and changing the volume using blue tack. But they have different drag coefficient and it would also be a different variable. Also using stokes law μ=(2r^2 g(ρ_(sphere)-ρ_fluid ))/9v, how do i calculate the velocity as it fall since it always decelerate? I think your suppose to use the terminal velocity? Thank you for reading!!