Physicists from the FOM Foundation and the University of Amsterdam have discovered that the ancient Egyptians used a clever trick to make it easier to transport heavy pyramid stones by sledge. If a heavy sledge is pulled over dry sand, a pile of sand accumulates in front of it. If a heavy sledge is pulled over wet sand, this does not happen.
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. If they use the right amount of water, the number of workers needed to pull the sledge can be halved!
We think Egyptians knew of this physics trick. A wall painting in the tomb of Djehutihotep (above) clearly shows a person standing on the front of the pulled sledge and pouring water over the sand just in front of it
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