But how did the Egyptians overcome the intense friction, sliding such heavy objects -- some stones weighed more than 9,000 pounds -- across the sandy desert? A new study by researchers at the University of Amsterdam offers a surprisingly simply solution to the friction query: they used water.
In their science paper, published this week in the journal Physical Review Letters, the researchers demonstrate how application of water stiffens sand, allowing heavy objects to slide across with less force.
Sand stiffens in the presence of water due to what scientists call "capillary bridges," whereby -- at the molecular level -- sand and water bind together.
“In the presence of the correct quantity of water, wet desert sand is about twice as stiff as dry 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,” the scientists explained.
The theory isn't completely out of the blue; an ancient painting on a tomb wall at Djehutihotep depicts a man pouring water onto the sand in front of a stone.
“Besides revealing something about the ancient Egyptians, the results are also interesting for modern-day applications," the study's authors wrote. "We still do not fully understand the behavior of granular material like sand. Granular materials are, however, very common. Other examples are asphalt, concrete and coal.”
“The research results could therefore be useful for examining how to optimize the transport and processing of granular material, which at present accounts for about ten percent of the worldwide energy consumption.”