Researchers from the FOM Foundation and the University of Amsterdam believe they have discovered the method by which ancient Egyptians transported statutes and large stones used to build their pyramids: wet sand. The scientists were able to reduce the friction of sand by pouring the correct amount of water on it, enabling them to more easily transport an object along its surface.
The formation of capillary water bridges increases the shear modulus of the sand, which facilitates the sliding. Too much water, on the other hand, makes the capillary bridges coalesce, resulting in a decrease of the modulus; in this case, we observe that the friction coefficient increases again.
The theory is seemingly supported by the discovery of a wall painting discovered in the tomb of 12th Dynasty ruler Djehutihotep, which shows a figure pouring water out in front of a statue transported by sled.
image via Phys.org