A lever is a simple machine that consists of a stick, a beam, or a plane and a balance point. Typically, when a force is applied at one point of the plane, it causes the load present at another point of the plane to move. The movement of the load takes place through the fulcrum. Hence, the fulcrum acts as a balance point in a simple lever machine.
Classes of Lever Simple Machine
The position of the three points, namely, force, load, and the fulcrum, is responsible to decide the class of the lever. The following are the three classes of a lever simple machine:
1. First Class
In this class of the lever, the fulcrum is located in the middle of the plane. The force is applied at one end of the plane, whereas the load is kept at the other end. For example, seesaw, scissors, plier, etc.
2. Second Class
In the second class of lever, the load is present at the middle of the plane. The fulcrum is located at one end, whereas the force is applied at the opposite end. For example, wheelbarrow, nutcracker, stapler, etc.
3. Third Class
In the third class of lever, the fulcrum is present at one end of the beam and the load is present at the opposite end. The force is applied to the middle of the plane. For example, a hockey stick, hammer, rake, etc.
Examples of Lever Simple Machine
1. Nut Cracker
A nutcracker is a prominent example of a second-class lever simple machine. Here, the fulcrum is located at one end of the machine, and the load or the nut, in this case, is placed in the middle. The force required to break the nut is applied to the end that is present opposite to the fulcrum.
Seesaws demonstrate the working of a first-class lever simple machine in the simplest possible way. Here, the fulcrum is located in the middle of an iron rod. The child sitting on one end of the beam acts as a load, while the child sitting on the opposite end applies the necessary force to move the load.
The pivot along which the complete structure of a pair of scissors moves is located in the middle. The load, i.e., the paper or cloth is placed between the blades of the scissors at one end, whereas the user exerts mechanical force to the opposite end. The applied force gets transferred to the load through the fulcrum or the pivot, thereby causing the deformation of the load. Hence, a pair of scissors act as a first-class lever simple machine.
In terms of working, a plier is very much similar to that of a pair of scissors. It is yet another example of a first-class lever machine where the force is applied at one end, the load is placed at the opposite end, and the balance point is present in the middle.
The balance point or the fulcrum of a stapler is present at one edge, whereas the force is applied to the opposite end. The load or the sheets of paper are placed in the middle. Hence, a stapler is a classic example of second-class lever simple machines.
A wheelbarrow consists of a metallic container that is attached with handles at one end and a wheel at the other end. Here, the wheel acts as a fulcrum or the balance point, the load is placed in the middle, and the push force is applied to the handles. Therefore, the arrangement forms a second-class lever simple machine.
7. Human body
Various joints in the human body function on the basic principle of a lever simple machine. These body parts include the elbow joint, Achilles tendon, the joint between hummers and radius-ulna, the joint between the skull and the atlas vertebrae, etc.
When a broom is used for sweeping dirt, it acts as a third-class lever simple machine. This is because the load is present at the one end of the broom, i.e., on the brush side, the effort or the force is applied in the middle, and the pivot is located at the top.
Hammer is yet another example of a third-class lever machine. The force is applied at the centre, the load or the reaction of the force is observed at the end, and the pivot is formed on the opposite end.
10. Balance Scale
A balance scale makes use of a pivot in the middle of a beam. On either side of the scale, containers are attached that are used to contain the standard and the unknown weights. This means that the fulcrum is present in the middle, whereas the load and effort are present on either side of the beam. Hence, a balance scale is one of the best examples of a first-class lever simple machine.