The question of just how an ancient civilization—without the help of modern technology—moved the 2.5 ton stones that made up their famed pyramids has long plagued Egyptologists and mechanical engineers alike. But now, a team from the University of Amsterdam believes they’ve figured it out, even though the solution was staring them in the face all along.
It all comes down to friction. See, the ancient Egyptians would transport their rocky cargo across the desert sands, from quarry to monument site with large sleds. Pretty basic sleds, basically just large slabs with upturned edges. Now, when you try to pull a large slab with upturned edges carrying a 2.5 ton load, it tends to dig into the sand ahead of it, building up a sand berm that must then be regularly cleared before it can become an even bigger obstacle.
Wet sand, however, doesn’t do this. In sand with just the right amount of dampness, capillary bridges—essentially microdroplets of water that bind grains of sand to one another through capillary action—form across the grains, which doubles the material’s relative stiffness. This prevents the sand from berming in front of the sled and cuts the force required to drag the sled in half. In half.
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