Introduction
A lever is a rigid rod capable of turning around a fixed axis called a fulcrum. It functions on the principle of moments. A lever has three parts: the load arm, the effort arm, and the fulcrum. The distance of the load from the fulcrum gives the length of the load arm, whereas the distance of the point of application of effort from the fulcrum gives the length of the effort arm. Based on the position of the fulcrum, levers can be categorized into three types: Class I, Class II, and Class III. Some common examples of levers we come across daily are see-saws, sugar tongs, scissors, nail clippers, etc.
Class I Lever
In the Class I lever, the fulcrum lies in the centre while the load and effort lie on either side. The load arm of the class I lever may be equal to, less than, or longer than the effort arm. Thus its mechanical advantage can be equal to, more than, or less than 1.
Some examples of class I lever include a see-saw, pair of scissors, beam balance, claw hammer, pliers, crowbar, spade turning soil, etc.
Class II Lever
In the class II lever, the load lies in between the point of effort and the fulcrum. Since the load arm of this class of lever is always smaller than the effort arm, their mechanical advantage is always greater than 1. These levers are hence forced multipliers.
Some examples of class II levers include bottle openers, wheelbarrows, nutcrackers, lemon crushers, oars for rowing boats, etc.
Class III Lever
In the Class III lever, the effort lies between the fulcrum and the load. Since the load arm of this class of levers is always longer than the effort arm, the mechanical advantage of the class III lever is always less than 1. These levers are speed multipliers.
Some examples of class III levers include sugar tongs, tweezers, hammers, knives, foot treadles, spade lifting coal, etc.
Compound Levers
A combination of multiple classes of levers gives a compound lever. In such levers, the force applied on one type transfers the force to another lever and yields the result. Examples include nail clippers, a combination of class II and class I lever.
Some Examples of Levers Found in the Human Body
Head-Neck Joint Region: Class I Lever
The atlanto occipital joints are synovial joints connecting the spine to the skull. It serves as a class one lever when we nod our heads back and forth. The fulcrum lies in the centre where the occipital bone attaches to the atlas vertebra. The front of the skull acts as the load, and the effort is at the back end applied to the contraction of the neck muscles.
Leg-Feet Joint Region: Class II Lever
When one tries to lift his body on his toes, the entire musculoskeletal system of the leg-feet region behaves as a class II lever. Here the toes at one end act as the fulcrum, the muscles on the other end act as the effort, and the body lies in the middle that is lifted as load.
Forearm: Class III Lever
When we try to lift a load in our hand, the forearm behaves as a class III lever. The load lies at one end, the fulcrum is at the elbow, and the effort is in between applied by the arm muscles.
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The ratio between the length of the effort arm of the lever to the length of its load arm is called its mechanical advantage. Scissors used by tailors have long load arms (the sharp ends) and short effort arms (the handle). Hence, the ratio of the length effort arm to the load arm will be less than 1. Thus, it is a speed multiplier. A wheelbarrow acts as a class II lever because, in this system, the fulcrum lies at one end of the wheels attached to the front of the cart. The load between the cart and the effort is on the handles on the other end. Simple machines reduce our efforts by overcoming a large amount of force or by increasing the speed by applying force at a convenient point and in the desired direction. Levers work on the principle of moments. That says that the clockwise moment of load about the fulcrum equals the anticlockwise moment of effort about the fulcrum. Load refers to the force to be overcome by the machine, and effort means the force applied on the machine to help it overcome the load. Types of Levers FAQs
What do we mean by the mechanical advantage of a lever?
Scissors used by tailors are force multipliers or speed multipliers?
Why is Wheelbarrow a class II lever?
What are simple machines?
What is the principle of levers?
What do we mean by load and effort?
