A friend of mine and I are conducting an experiment to find the relationship between terminal velocity and radius of a sphere (i.e trying to confirm Stokes law). We are using spheres ranging from 1.5mm radius to 3mm, and dropping them in a large beaker (Of radius 7cm) filled with canola oil, using a tracker software to measure the terminal velocity. Terminal velocity is indeed reached for all balls, and we get consistent values of Vt for each repition of the experiment.
Our results, however, are inconclusive. We have been trying to figure out why for the last week or so to no avail. Our teacher has no idea either.
The problem: We assumed Stokes law would apply to this scenario (perhaps a mistake?), and that Terminal velocity would be proportional to r^2 yet our results show overwise. (And Terminal velocity plotted over Radius seems to be almost exactly linear) Here is our plot of V over R^2:
Sorry for the unfinished formatting; I quickly entered it in plot.ly because I thought google sheets wasn't scaling properly. Since the trendline couldn't fit within the uncertainty bars assumed there must be something else happening to cause the mismatch with what was expected.
Does anyone have any ideas as to why this is? We have double checked everything and are 100% sure we have made no measurement errors. Perhaps it is simply because we do not have enough data points? Wet tried calculating the terminal velocity from the Stokes formula, and it is consistently higher than what we measured in the experiment. We have absolutely no idea what could be causing this. All help is appreciated.