The physicists placed a laboratory version of the Egyptian sledge in a tray of sand. They determined both the required pulling force and the stiffness of the sand as a function of the quantity of water in the sand. To determine the stiffness they used a rheometer, which shows how much force is needed to deform a certain volume of sand. Experiments revealed that the required pulling force decreased proportional to the stiffness of the sand...A sledge glides far more easily over firm desert sand simply because the sand does not pile up in front of the sledge as it does in the case of dry sand.
These experiments served to confirm what the Egyptians clearly already knew, and what we probably already should have. Artwork within the tomb of Djehutihotep, which was discovered in the Victorian Era, depicts a scene of slaves hauling a colossal statue of the Middle Kingdom ruler and in it, a guy at the front of the sled is shown pouring liquid into the sand. You can see it in the image above, just to the right of the statue's foot...more