“…However, as already long discussed in the literature, this interpretation is not as straightforward as it seems 8,9,11,12,14,15 . Confusion between the two independent questions formulated in the introduction has led some to refute the decrease of effective friction with volume because of the questionable meaning of the Heim's ratio 15 . Its limitations as a measure of the effective friction have long been recognized in the literature, based on the fact that its definition does not involve the displacement of the centre of gravity 16 , the spreading of mass or the role of the topography 8,9,12,14,15 .…”