The mystery surrounding the movement of massive stone blocks in ancient Egypt has been solved by scientists finally, based on the study of some artifacts from the ancient days.
It remained a mystery that the pyramids of Egypt, built with stones weighing 25 to 80 tons, posing a challenge to the modern world about the way they were transported hundreds of miles to reach the place.
The famous pyramids of Egypt were constructed using millions of large, granite and limestone blocks, and an estimated 2.3 million.
Researchers from the University of Amsterdam unravelled the mystery last week suggesting a surprisingly simple way. The study, published in the journal Physical Review Letters, says the ancient Egyptians used wet sand to mobilize the blocks, a simple trick that reduced friction with the sand during the long hauls across the desert.
The study unveiled a new technology used by the Egyptians, who had built the pyramids. It has also proved wrong the old-belief that they used wooden sledges to move stones.
Or, constantly clearing the sand to move the blocks would also be tedious. Researchers from Amsterdam finally looked at other methods and zeroed in on one old painting in the ancient tomb of Djehutihotep to explain their finding.
The painting shows the process of wetting the sand in front of a sledge. The drawing shows 172 Egyptian workers transporting a 23-foot-tall statue fitted to a sledge and one worker at the front of the sledge was clearly seen pouring water onto the sand in the front, paving the way for smooth movement of the heavy sledge.
“Egyptologists had been interpreting the water as part of a purification ritual, and had never sought a scientific explanation,” said Daniel Bonn, lead researcher of the study. “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.”
Once the blocks were on site, the ancient Egyptians are thought to have used ramps to put the blocks into place. But this too requires research and a perfect explanation. Here is the painting:
(Wall painting from the tomb of Djehutihotep. A large statue is being transported by sledge. A person standing on the front of the sledge wets the sand. Source: Al-Ahram Weekly, 5-11 August 2004, issue 702).
Researchers conducted experiments, which have demonstrated that the correct amount of dampness in the sand halves the pulling force required. The physicists then placed a laboratory version of the Egyptian sledge in a tray of sand. They determined both the required pulling force and the stiffness of the sand as a function of the quantity of water in the sand. To determine the stiffness they used a rheometer, which shows how much force is needed to deform a certain volume of sand.
Experiments revealed that the required pulling force decreased proportional to the stiffness of the sand. Capillary bridges arise when water is added to the sand. These are small water droplets that bind the sand grains 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 Egyptians were probably aware of this handy trick. A wall painting in the tomb of Djehutihotep clearly shows a person standing on the front of the pulled sledge and pouring water over the sand just in front of it.
Besides revealing something about the Egyptians, the results are also interesting for modern-day applications. We still do not fully understand the behaviour 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 optimise the transport and processing of granular material, which at present accounts for about ten percent of the worldwide energy consumption.
The research was supervised by group leader professor Daniel Bonn and is part of the FOM programme ‘Fundamental aspects of friction’.