the most basic of all machines
A lever consists of a rod or
plank that is free at both ends, and some steady
object on which the plank can rest. The braced,
or fixed, part is called the fulcrum.
The distance from the load to the fulcrum is the load
arm. The distance between the fulcrum and
the lifting force is the effort arm.
In its simplest form, the
crowbar, the lever is a device that magnifies the
effect of a small effort to move a large weight.
But inverting the effort and the fulcrum changes
the relationship; gripping a fishing pole and
flipping a trout out of the water requires much
more effort than the fish weighs, but the extra
effort buys the longer distance the fish travels.
How and Why a Lever
Levers work according to a
simple formula known as the Law of
Equilibrium. This law is illustrated by the
diagram below: the effort multiplied by its
distance from the fulcrum (effort arm) equals the
weight multiplied by its distance from the
fulcrum (load arm). Thus, two pounds of effort
exerted at a distance of four feet from the
fulcrum will raise eight pounds located one foot
from the fulcrum.
Classes of Levers
Levers have the fulcrum
placed between the load and the effort,
as in a seesaw, crowbar, and balance
scale. If the two arms of the lever are
of equal length, the effort must be equal
to the load. To lift 10 pounds, an effort
of 10 pounds must be used. If the effort
arm is longer than the load arm, as in
the crowbar, the effort travels farther
than the load and is less than the load.
A pair of scissors is a double lever
of the first class.
Levers have the load
between the effort and the fulcrum. The
best example of a second-class lever is
the wheelbarrow. The wheel is the
fulcrum, the handles take the effort, and
the load is placed between them. The
effort always travels a greater distance
and is less than the load. A nutcracker
is a double lever of this class.
Levers have the effort
placed between the load and the fulcrum.
The effort always travels a shorter
distance and must be greater than the
load. The forearm is a third-class lever.
The hand holding the weight is lifted by
the biceps muscle of the upper arm which
is attached to the forearm near the
elbow. The elbow joint is the fulcrum.
Levers combine two or more
levers, usually to decrease the effort.
By applying the principle of the compound
lever, a person could use the weight of
one hand to balance a load weighing a
Robert O'Brien Machines
New York: Time Incorporated, 1964
The World Book Encyclopedia
Chicago: World Book-Childcraft International,
Questions or comments about