The lever is a simple machine consisting of a bar supported at some
stationary point along its length and used to overcome resistance at
a second point by application of force at a third point. The
stationary point of a lever is known as its fulcrum.
The Lever Principle has been found by experiment where two equal forces
were acting in opposite directions, i.e., clockwise and counterclockwise, and
applied to a uniform lever at equal distances from the fulcrum counteract each
other and established a state of equilibrium, or balance, in the lever.
Experiment has also shown that two unequal forces when acting in
opposite directions will bring about an equilibrium when the product
of the magnitude of one force and its effort arm, or lever arm (the
distance of its point of application from the fulcrum), is equal to
the product of the magnitude of the other force and its effort arm.
In physics the product of a force by its effort arm is called moment
of the force. The general conclusion known as the principle of moments
states that equilibrium is established when the sum of the moments of
the forces acting in a clockwise direction is equal to the sum of the
moments of the forces acting in a counterclockwise direction. It is
possible, as a result, to overcome a very large force at a short
distance from the fulcrum with a very small force at a great distance
from the fulcrum. Archimedes is supposed to have boasted, having the
lever in mind, that given a place to stand he could move the Earth.