The question about how an ancient civilization, without any help of the modern technology which we have today, moved the 2.5-ton stones that made up their famous pyramids, has long plagued Egyptologists, as well as mechanical engineers alike. But now, one team from the Amsterdam University believes that they have figured it out, although the solution was right in their face for a long time.
It actually all comes down to friction. The ancient Egyptians would transport their rocky cargo all over the desert sands, from a quarry to monument site with large sleds. Pretty basic sleds, basically just large slabs with some upturned edges. Now, if you try to pull a big slab which has upturned edges carrying a 2.5-ton load, it will dig into the sand ahead of it, building up a sand berm which has to be regularly cleared before it can become a huge obstacle.
However, wet sand does not do this. In sand, with only the right amount of dampness, as well as capillary bridges, essential microdroplets of water which bind grains of sand to one another through capillary action, from across the grains, which actually doubles the relative stiffness of the material. This will prevent the sand from berming in front of the sled, and it will also cut the force which is required to drag the sled in half.
As the press release of UvA explained:
The physicists created a laboratory version of the Egyptian sled in a tray of sand. After that, they determined both the required pulling force and the stiffness of the sand as a function of the quantity of water which was in the sand. In order to determine the stiffness, they utilized a rheometer, which actually shows how much force was needed in order to deform a certain volume of sand.
The experiments which were made also revealed that the required pulling force decreased the proportional to the stiffness of the sand. A sled will slide far more easily over firm desert sand simply as the sand does not come in front of the sled as it actually does in the case of dry sand.
These experiments were done in order to confirm what the Egyptians clearly already knew, and what we probably already have. The artwork within the tomb of Djehutihotep, which has been discovered in the Victorian Era, actually depicts a scene of slaves who are pulling a colossal statue of the Middle Kingdom ruler and in it, there is a guy at the front of the sled that is shown to pour the liquid into the sand.
Featured Image Credit: Daniel Bonn