While I agree that cohesion could explain the phenomena where is the center of gravity for the full and empty container? Most of the shampoo bottles I have seem to have thicker bottoms than sides or tops. This seems to be a case where very careful measurement is needed. Or perhaps more sampling. Do the experiment with 50 shampoo bottles of the same manufacture (and perhaps even bought at the same time to get a common production run).
While I agree that cohesion could explain the phenomena where is the center of gravity for the full and empty container? Most of the shampoo bottles I have seem to have thicker bottoms than sides or tops. This seems to be a case where very careful measurement is needed. Or perhaps more sampling. Do the experiment with 50 shampoo bottles of the same manufacture (and perhaps even bought at the same time to get a common production run).