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phys.org - "Workers dragged Forbidden City stones along roads of artificial ice"

Researchers at the University of Science and Technology in Beijing have revealed that, in the 15th and 16th Centuries, the Chinese used artifical roads of ice to help transport the stones used to build China's Forbidden City.  This demonstrates an advanced understanding of friction and lubrication for the time.

"The workers placed the stone on a sledge, which they then dragged along an artificial ice path, created by pouring well water onto the ground and then allowing the water to freeze. They dug wells every half kilometer. By pouring water over ice that had already frozen, they created a liquid surface that decreased the friction between the sledge and the ice. The workers had time to move the sledge across the liquid film before it froze." - Marcia Mallory, phys.org

Read the full story here:

http://phys.org/news/2013-11-workers-forbidden-city-stones-roads.html