In Egypt's tomb of Djehutihotep, a wall painting depicts someone pouring water into the sand in front of one of the sledges that hauled the blocks used in the construction of the pyramids. According to new research, they had a good reason for doing so – by wetting the sand, as little as half as much pulling force would have been required to move those sledges.

The research was conducted by a team from the Foundation for Fundamental Research on Matter, and the University of Amsterdam. They built miniature versions of the laden sledges, which they pulled through trays filled with both dry and moistened sand.

When an optimum amount of water was added to dry sand, capillary action bonded the individual grains together, causing the material to become approximately twice as stiff as it had been. This stiffness kept the sand from piling up in front of the sledge, making it much easier to pull. Too much water, however, saturated the sand and caused it to lose that stiffness.

It's similar to the building of sand castles, in which damp sand holds together better than dry or sodden sand.

The painting from the tomb of Djehutihotep

While there currently aren't many people attempting to build giant pyramids, the researchers believe that their findings could nonetheless have some practical applications. In particular, the knowledge could be used "to optimize the transport and processing of granular material" such as asphalt, concrete or coal.

A paper on the research was recently published in the journal Physical Review Letters.

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