How the ancient Egyptians managed to move multi-ton stones to build the pyramids without modern technology has long baffled scientists, but now researchers think they've learned the secret.
According to the American Physical Society, a team from the University of Amsterdam showed that adding water -- but not too much -- to sand would reduce friction enough to make sliding an object on it easier.
The physicists conducted an experiment that showed how "capillary water bridges" formed with the addition of water, aiding in sliding. Too much water, however, would actually increase sliding friction.
"Our results, therefore, show that the friction coefficient is directly related to the shear modulus; this has important repercussions for the transport of granular materials. In addition, the polydispersity of the sand is shown to also have a large effect on the friction coefficient," the authors wrote of the technical details in the abstract for the study published in Physical Review Letters.
Physicists conducted an experiment that showed dry sand would build up in front of a load-bearing sled, while sand that was too wet would only increase friction. Sand that was just wet enough would make pulling the sled significantly easier. (Image source: University of Amsterdam/Fundamental Research on Matter)
Put more simply, the American Physical Society explained that dry sand would build up in front of a sled with a heavy load, while too much water decreased the sand's stiffness, making it difficult for anything to move on top.
The application of the right amount of water to the sand under the load-bearing sled cut the amount of force needed to move it in half.