Types of levers

Physics defines the lever as a “linear transmission” system consisting of a rigid bar that is supported by a specific point (known as a support point) and subjected to a force (known as F or Power) serves to overcome a certain resistance (R).


Since ancient times the lever has existed in civilization, although its use and theorization is attributed to Archimedes, the great Spartan mathematician, who is identified as the author of the phrase “give me a foothold and I will move the world”, referring to the Lever. In today’s times, this mechanism or system is part of our lives, being the basis of everyday tools.

However, before we go on to define the existing lever types, as well as the everyday examples where we can find them, it is necessary to identify the parts or elements that make up that system. In this sense, in a lever system, there will always be the following elements:

Strength (F): Also called Power, it refers to the amount of force that the impeller must print at a particular point on the lever in order to overcome an opposing resistance or other force. This force can be applied manually by a human, or through machines or motors. That is, Power is the amount of force used by us to the lever, to help us move the object we want to move.

Power Arm (BP): Consists of the distance between the point where the Power (F) is applied and the support point of the lever.

Support point (O): the place where the lever is rotated and where the Power is printed, which is transmitted to the Resistance, allowing its expiration.

Resistance (R): this is the force we intend to overcome by using the lever and applying our power.

Resistance Arm (BR): Is the distance between the resistance and the support point.

With these elements and their location within the lever system clear, we can then go on to describe the existing lever types, which are classified according to the place they occupy F, R and O within the system. In this sense we can identify three different types of levers, which are as follows:

First Grade Lever: it is the basic lever, in which the Support Point (O) is located between the Power (F) and the Resistance (R). Its effectiveness will depend on whether the support point is closer to the Resistance than the Force, i.e. the Resistance Arm (BR) is less than that of the Power Arm (BP). With this type of lever you can overcome great resistances. In everyday life we can find examples of first-degree levers in tools such as the pliers, goat’s foot or hook, as well as in the Roman scale.

Second-degree lever: In this system, resistance (R) is located between Power (F) and Support Point (O), making the Resistance Arm (BR) always much lower than the Power Arm (BP), thus allowing the resistance to be overcome with the least amount of power possible. An example of second-degree levers is the forklift, where the Power would be exercised by the wheelbarrow, the Resistance (R) would be located where the load is carried, while the support point (O) would be located on the wheel of the forklift , thus causing the Resistance Arm (BR) to be much shorter than the Power Arm (BP). Likewise, the nutcracker represents another example of a second-degree lever.

Third-degree lever: In this case the Power (F) is applied in a place located between resistance (R) and Support Point (O), resulting in the Resistance Arm (BR) always being greater than the Power Arm (BP) so the effort applied siem pre will outperform the resistance to defeat. This type of lever is used in precision tasks, where a priori The Power (F) is greater than the Resistance (R). An example of a third-degree lever is eyebrow-raising tweezers or fishing rod.

It is important to note that according to the dictation of the Law of the Lever, it is in balance when the product of the Power (F) by the Power Arm (BR) is equal to the product of the Resistance (R) by the Power Arm (BR). That is, the lever is in equilibrium when it responds to the following formula:

F.BP – R.BR

From what can be concluded that the greater the distance between the Power (F) and the Support Point (O) i.e. the greater the Power Arm (BP) the smaller the Power (F) to apply in order to overcome a specific resistance (R). The higher The Power Arm (BF) the lower Force (F).

Image source: concurso.cnice.mec.es

Types of levers
Source: Education  
August 22, 2019


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