Levers: Raising the Moai on Easter Island

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.

The most common lever systems have four components: a lever arm, or length of relatively stiff material; a fulcrum on which a lever balances or pivots; the load, which is the weight or resistance that needs to be moved; and effort, or the force applied to the lever. In a class one lever (there are three classes of levers in all), the fulcrum is positioned between the load and the point where the effort is applied. One end of the lever arm goes under the object to be moved. When downward force is applied to the other end of the arm, the arm pivots on the fulcrum. This pivoting action raises the end of the arm under the object to lift it.

A lever's mechanical advantage -- that is, the degree to which it amplifies force -- is determined by the ratio of its lever arms. The more you increase the distance over which you exert force, the more you can decrease that force and still get the job done. The closer the fulcrum or pivot point is to the weight, the less force you have to use and the easier it is to lift the weight. If a lever arm is positioned across a fulcrum so that the side from which you'll exert force is 10 times longer than the load side, you can use it to lift a 1,000-pound object by applying a force of only 100 pounds. To do so, however, you'll have to push your lever arm 10 times farther than the load moves.

Compare the weights of Egyptian obelisks and Rapa Nui moai to other objects in this NOVA classroom activity.

• Using a sketch, explain how the force applied by a lever is affected by its distance from the fulcrum.
• In what ways is using a screwdriver to remove the lid of a paint can similar to using a lever to turn the moai on its sled? Can you think of other everyday examples in which levers or lever actions are used to make jobs easier?
• Why should the task get easier once the moai passes the 45-degree angle?
• Why was friction important as the moai was raised?
• Before modern machines, humans built and moved many large things using simple mechanical principles. Do you think that those works (Easter Island, the Great Pyramids, Stonehenge) are more significant than the current large-scale projects that people build (skyscrapers, sporting venues)? Explain why or why not.