Raising an Obelisk: An Engineering Puzzle

Archaeological evidence suggests that ancient peoples were able to move enormous objects, some in excess of several tons, without the mechanical advantage provided by modern inventions such as the crane. Think of the colossal carved statues, or moai, on Easter Island; the massive obelisks in Egypt; and the stone monoliths at Stonehenge. Without mechanical equipment, how were these feats achieved? With simple machines, namely levers, which are designed to make work easier for humans by moving or manipulating objects using less physical effort.

In this video segment adapted from NOVA, two different teams using two different approaches tackle the challenge of erecting an obelisk in a given amount of time using only materials and techniques available to the ancient Egyptians. From the start, both teams knew that the height and weight of the granite object was such that it could not be lifted or pushed up into place relying solely on the physical strength of workers. So they used levers. Among the most basic and time-tested of all machines to make use of mechanical advantage, levers were used to prop up the obelisk to a position from which it could then be set upright. But levers were only part of the ancient Egyptians' -- and the teams' -- designs; gravity, friction, and tension were also expected to do some of the work.

Though only one approach proved successful, both teams had worked through the engineering design process in hopes of improving their chances of raising up the obelisk. They identified the challenge, researched which materials they thought the Egyptians might have used to address it, and made drawings and plans. One team even tested its ideas using a scale model. Both teams followed the engineering design process so that when it came time to implement their designs, they could feel confident that they'd arrived at the plan they thought would work best.

Discover how levers work by raising a brick with shish kebab skewers in this NOVA classroom activity.

• What is the role of the deep groove on the side of the obelisk's pedestal?
• What did the first team think was its mistake?
• How do you think using a model was helpful to the first team of engineers?
• Why did the second team use sand? What force of nature played a role?
• Do you think a model could have been helpful to the engineers using the second method? How?
• Was the theory behind either of the ways to raise an obelisk incorrect?