Have you ever wondered how the Egyptians were able to build such massive and impressive structures? Constructing the pyramids involved pulling massive stones and statues which weighed over 2.5 tons, an extraordinary feat considering they did not have any of the modern mechanical devices we have today. Thanks to an international team led by Daniel Bonn from the University of Amsterdam, we now know how they did it.
Faced with the challenge of moving materials of massive weight through the desert, the Egyptians had to innovate. All there is in the desert is sand, sand and more sand, so they had to work with what they had. It turns out that adding a small amount of water to sand significantly reduces sliding friction, since water binds grains of sand together. This trick allowed Egyptians to cut the amount of workers needed in half, greatly enhancing the building processes. The optimal level of water to make this work falls between two and five percent of the volume of sand. Check below for a comparison, where sand accumulates in front of the sled when it’s pulled over dry sand (left), but not with wet sand (right).
The answer to this question has been quite literally staring us in the face for a long time, as a wall painting from the tomb of Djehutihotep depicts a worker pouring water on the sand in front of a sled carrying a colossal statue. For many years Egyptologists interpreted the water as part of a purification ritual, and not for any practical purposes.
[h/t IFL Science]