The ancient Egyptians who built
the pyramids may have been able to move massive stone blocks across the
desert by wetting the sand in front of a contraption built to pull the
heavy objects, according to a new study.
Physicists at
the University of Amsterdam investigated the forces needed to pull
weighty objects on a giant sled over desert sand, and discovered that
dampening the sand in front of the primitive device reduces friction on
the sled, making it easier to operate. The findings help answer one of
the most enduring historical mysteries: how the Egyptians were able to
accomplish the seemingly impossible task of constructing the famous pyramids.
To
make their discovery, the researchers picked up on clues from the
ancient Egyptians themselves. A wall painting discovered in the ancient tomb
of Djehutihotep, which dates back to about 1900 B.C., depicts 172 men
hauling an immense statue using ropes attached to a sledge. In the
drawing, a person can be seen standing on the front of the sledge,
pouring water over the sand, said study lead author Daniel Bonn, a
physics professor at the University of Amsterdam. [Photos: Amazing Discoveries at Egypt's Giza Pyramids]
"Egyptologists thought it was a purely ceremonial act," Bonn told Live Science. "The question was: Why did they do it?"
Bonn and his colleagues constructed miniature sleds and experimented with pulling heavy objects through trays of sand.
When
the researchers dragged the sleds over dry sand, they noticed clumps
would build up in front of the contraptions, requiring more force to
pull them across.
Adding water to the sand,
however, increased its stiffness, and the sleds were able to glide more
easily across the surface. This is because droplets of water create
bridges between the grains of sand, which helps them stick together, the
scientists said. It is also the same reason why using wet sand to build a sandcastle is easier than using dry sand, Bonn said.
But, there is a delicate balance, the researchers found.
"If
you use dry sand, it won't work as well, but if the sand is too wet, it
won't work either," Bonn said. "There's an optimum stiffness."
The
amount of water necessary depends on the type of sand, he added, but
typically the optimal amount falls between 2 percent and 5 percent of
the volume of sand.
"It turns out that wetting Egyptian deserts
and can reduce the friction by quite a bit, which implies you need only
half of the people to pull a sledge on wet sand, compared to dry sand,"
Bonn said.
The study,
published April 29 in the journal Physical Review Letters, may explain
how the ancient Egyptians constructed the pyramids, but the research
also has modern-day applications, the scientists said. The findings
could help researchers understand the behavior of other granular
materials, such as asphalt, concrete or coal, which could lead to more
efficient ways to transport these resources.
Follow Me On WWW.TWITTER.COM/CRISAIGBE
