Seesaws, tweezers and the bones in your ear all obey one rule
A lever is nothing more than a rigid bar turning on a pivot, yet it lets a small push lift a heavy load. The trade is distance: the end you press travels further than the end doing the lifting. Archimedes captured the idea in his boast that, given a place to stand, he could move the world.
The rule behind every lever is simple. If there is no friction at the pivot and the bar does not bend, the power going in equals the power coming out. The force a lever delivers, compared with the force you apply, then depends only on how far each force acts from the pivot, or fulcrum. Push twice as far from the fulcrum as the load sits and you exert half the effort, at the cost of moving twice the distance. This is the law of the lever, and the ratio is its mechanical advantage.
Engineers sort levers into three classes by what sits in the middle. In the first class the fulcrum is between your effort and the load, as in a seesaw or a crowbar, and the advantage can be more or less than one. In the second, the load is in the middle, as in a wheelbarrow or a nutcracker, so the lever always multiplies force. In the third, your effort is in the middle, as in tweezers or a fishing rod, which sacrifices force to gain speed and reach. Chaining levers so each one pushes the next makes a compound lever, and the tiny malleus, incus and stapes in the middle ear work this way, passing sound from the eardrum to the cochlea.
Levers are among the oldest human tools. The historian Autumn Stanley suggests the digging stick was the first, which would make prehistoric women its inventors. Ancient Egyptians used lever-based balance scales around 5000 BC, and Mesopotamians invented the shadouf, a pivoting pole for lifting water, around 3000 BC. The earliest surviving writings on the subject date from the third century BC and are traditionally credited to Archimedes.
Even the word carries the idea of ease. It reached English around 1300 from the Old French verb for raising, which comes from the Latin levis, meaning light, and ultimately from an ancient root for light, easy or nimble.
Source: Lever
