Inspired by a 4000-year-old painting, physicists have figured out how ancient Egyptians may have dragged heavy statues across the desert. The image (above), found in an ancient tomb at Dayr al-Barsha, about 320 kilometers south of Cairo, depicts 172 workers dragging a colossal statue of Djehutihotep, a provincial ruler, on a wooden sled, while one worker pours what could be water in front of the procession. Although previous experiments suggested that adding water to sand would increase rather than decrease friction, a team of scientists wondered whether just the right amount of water could help bond grains of sand together, making the sand more rigid and reducing friction. To find out, the researchers measured the force it took to drag a sandpaper-bottomed sled carrying a 2-kilogram weight across a slightly damp bed of sand. Increasing the sand’s water content to 5% cut friction by as much as half, depending on the kind of sand the team tested. Beyond 5%, however, the water-sand mix lost its stiffness again. The results, reported in Physical Review Letters, could help manufacturers transport materials such as drink mixes or powders used in pharmaceuticals more efficiently, shaving a bit off the industry’s enormous carbon footprint. Another bit of ancient Egyptian wisdom revealed, thanks to modern science.
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