Classes of levers
Levers are divided into three classes, according to the way the load and force arms are arranged around the fulcrum.
First Class Lever
When the fulcrum lies between the force arm and the lever arm, the lever is described as a first class lever. In fact many of us are familiar with this type of lever. It is the classic teeter-totter example.
When the fulcrum is midway between the force and the load, there is no change in force, speed or distance.
Other first class levers include: a car jack, a pair of pliers, a pair of scissors, a water pump, a balance or pair of weigh scales, a crowbar, a claw of a hammer taking out a nail, or a lever with a rock as its fulcrum trying to lift another rock.
Second Class Lever
In the second class lever, the load arm lies between the fulcrum and the force arm. A good example of this type of lever is the wheelbarrow. The axle of the wheel serves as the fulcrum, the handles are the force arm, and the load is carried between the two in the bucket part of the wheel barrow.
In the second class lever, the fulcrum is usually closer to the load, which reduces the force needed to accomplish the work.
Some other examples of the second class lever are: a pair of nutcrackers, and a bottle opener.
Third Class Lever
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 employ 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.
Example of third class levers are: a fishing pole, a pair of tweezers, an arm lifting a weight, a pair of calipers, a person using a broom, a hockey stick, a tennis racket, a spade, or