Third Class Lever
What is a Third Class Lever?
In a third class lever, the force is between
the fulcrum and the load on the lever arm. Since the load is further from the
fulcrum than the applied force, the magnitude of the load is less than that of
the applied force. In a third class lever, the distance the load moves is
greater than the distance the force moves. Therefore a third class lever always
magnifies the distance moved and reduces the magnitude of the load. Examples of
third-class levers include fishing rods, an arm, a hammer, etc.
In this class of levers, the force arm lies between the fulcrum and the
load arm. Because of this arrangement, a relatively large force is required to
move the load. This is offset by the fact that it is possible to produce
movement of the load over a long distance with a relatively small movement of
the force arm. Think of a fishing rod! Because of this relationship, we often
use this class of lever when we wish to produce large movements of a small
load, or to transfer relatively low speed of the force arm to high speed of the
load arm. When a hockey stick or a baseball bat is swung, a third class lever
is in effect. The elbow acts as a fulcrum in both cases and the hands provide
the force (hence the lower arm becomes part of the lever). The load (i.e. the
puck or the ball) is moved at the end of the stick or bat. In a third class
lever there is usually a loss in force needed to accomplish the work, but a
gain in speed or distance. Examples of third class levers are: a fishing pole,
a pair of tweezers, an arm lifting a weight, a pair of callipers, a person
using a broom, a hockey stick, a tennis racket, a spade, or a shovel.
Mechanical advantage
- v A third-class lever allows a small load to be lifted by larger effort.
Characteristics
- v Because the effort is always closer to the fulcrum, the load is always less than the effort, but the load always moves through a longer distance than the effort.
