“Adding more evidence to the conclusion that Egyptians used water is a wall painting in the tomb of Djehutihotep. A splash of orange and gray, it appears to show a person standing at the front of a massive sledge, pouring water onto the sand just in front of the progressing sled. What this man was doing has been a matter of great debate and discussion.
“This was the question,” Bonn wrote in an e-mail to The Post. “In fact, Egyptologists had been interpreting the water as part of a purification ritual, and had never sought a scientific explanation. And friction is a terribly complicated problem; even if you realize that wet sand is harder – as in a sandcastle, you cannot build on dry sand — the consequences of that for friction are hard to predict.”
He said the experiment not only solved “the Egyptian mystery, but also shows, interestingly, that the stiffness of sand is directly related to the friction force.””