The Science Of How Cranes Work: The Lever, Part I

Have you ever wondered how certain technological items? Well, this article, plus the next three parts, serve to explain the science behind construction cranes. First, we will explain how a lever increases the crane's ability to lift really heavy loads. The next articles will investigate the role of the lever, the hydraulic cylinder, and the concept of mechanical advantage in the science behind construction cranes.

To a greater or lesser extent, all cranes employ the lever to lift really heavy loads. Balance cranes and all mounted cranes optimize lifting capacity through the lever. These cranes have a mechanical arm that acts as such a lever. Although the arm is usually accompanied by a complex system of pulleys, ropes, and chains, the lever is classified as a simple machine.

Scholars insist that the ancients practically applied the lever in the building of large temples, monuments, and fortifications. In fact, many conjecture that the Egyptians utilized the lever in the building of the Great Pyramids. However, most attribute the geometrical and mathematical theory behind the lever to the ancient Greeks, most particular Archimedes in the third century B.C.E. He famously quipped, "Give me a place to stand, and I shall move the Earth with a lever."

Since then, architects and engineers throughout history have optimized the lever for particular lifting purposes. A lever is defined as a rigid "bar" that rests on a pivot point, or fulcrum, where you apply an "effort" force to create a resulting "work" force that lifts some object.

Physicists categorize levers into three classes. First class describes levers where the fulcrum rests between the effort and lifting forces, as one sees in a seesaw or crowbar. Second class defines levers in which the load forces sits between the fulcrum and the applied force, such as a wheelbarrow. And finally, third class indicates levers in which one applies the effort force between the fulcrum and the load. For example, a set of tweezers is an example of third-class levers.

These classes define all possible levers, but why does this matter? Well, different classes of levers can lift loads of varying weights for numerous purposes. Most importantly, these levers manipulate the mathematical concept of Torque. In Physics, torque equals the effort force times the distance over which the force is applied. For example, applying 40 pounds of effort over five feet is much harder than applying a mere two pounds of effort over 100 feet. Both applications require the same amount of Torque to lift some object, but the second requires much less "effort" force for humans to apply. It literally requires less effort. This is why, for example, pulling a nail out of a board by hand is much harder than using a crowbar.

Be sure to catch our next article on pulleys in construction cranes.

Serving in the crane industry for decades, Barnhart Crane and Rigging Companying provides the best in Crane Service andMachinery Moving.