Why a Little Water Made Sand Firmer
A loaded sled does not just slide over desert sand: its runners push grains forward and sideways, building a mound that the sled must continually climb. Much of the effort goes into shoving this loose sand out of the way, not merely overcoming friction beneath the runners.
A small amount of water changes how the grains hold together. Thin films of moisture create tiny adhesive forces between neighboring grains, helping them form a firmer surface that can support the sled instead of flowing aside. The runners then make a shallower track, and less sand piles up in front of them.
The Difference Between Damp and Wet
The useful condition is damp, not soaked. With too little water, the grains remain loose; with too much, water can fill the spaces between them and the sand may lose the helpful stiffness. The goal is to strengthen the surface without turning it into mud.
That makes the method a practical engineering tradeoff: workers had to add enough water to firm the route, but not so much that the sled bogged down. The water worked mainly by changing the sand, not by acting as a lubricant beneath the stone. A small pour ahead of the runners could therefore spare a team the repeated work of hauling a heavy load through a ridge of its own making.
