Among the most used simple machines is the lever, since it allows to transmit force and displacement in an easier way and without making too much physical effort. This is why it is worth knowing in depth the types of levers and their uses in everyday life.
To easily understand what a lever is, you have to think of it as a rigid bar that moves on a fulcrum called the fulcrum, with the aim of amplifying the mechanical force applied to an object. It also serves to increase the distance traveled, thus facilitating different activities at the domestic and industrial level.
We say that we are facing a lever when the mechanism in question has 3 forces: The first is the support force or fulcrum that we have mentioned above, the second is the resistance or load and third is the power or effort that we have to apply to balance the load.
Archimedes defined the law of the lever in this way; the power (P) multiplied by its distance from the fulcrum (dP) is equal to the resistance (R) times its distance from the fulcrum (dR). The formula would be as follows: P x dP = R x dR. This means that if there is a greater distance between the fulcrum and the fulcrum when applying power, then we will have more advantage against resistance. This principle has been used for thousands of years to move heavy objects from one place to another, but there are several versions depending on the position of the power, the resistance and the fulcrum on each machine. For this reason, it is good to mention some examples of levers according to their type.
First class lever
The first degree lever is the easiest to understand, since it has the fulcrum in the center, between power and resistance, as if it were a balance, which means that to keep the load in balance, there would be You have to apply the same weight to the stem as there is to the resistance.
Among the first-class levers that we use the most in daily life are scissors. In this case, the power would be in the clamping rings, where we insert the fingers to exert pressure, the fulcrum would be the screw that is right in the center, while the resistance would be in the blades.
Second class lever
The second degree levers have the peculiarity that their fulcrum is at one end of the machine, while the power is at the other end, leaving the resistance or load in the center. One of the characteristics of these levers is that they require less effort to balance the resistance.
The wheelbarrows that are used in the garden and in construction are a clear example of a second degree lever, since the fulcrum is on the wheel and the power is exerted on the handles, leaving the resistance in the load carrier, that is to say , in the center of the tool. In this case, there is very little physical effort that must be made to keep the load in balance, but the higher the weight, the speed of transfer decreases.
3rd class lever
The third-degree lever has the resistance at one end and the fulcrum at the other end, therefore, the power is applied in the center of the system. This is the case with the fishing rod; the resistance is exerted by the fish that we have caught, the point of support is in the handle that we hold with one of the hands, while the power is applied towards the center of the rod with the other hand, in order to remove the fish. of the water.
The tweezers are also third-class levers, since the fulcrum is at the vertex where the two pieces meet, the resistance is at the tips with which we hold the object and the power must be applied in the center of the tweezers. This type of lever is very present in everyday life, in objects as common as a broom or a hockey stick.
History of the lever
The lever has been part of human daily life since prehistoric times. According to data collected by historians, in the year 3,000 BC. C. the levers were used in Mesopotamia to build cigoñales, machines used to extract water from rivers and reservoirs in order to supply a family or community.
One of the greatest Greek mathematicians, Papo of Alexandria, mentions the lever in a manuscript of the year 340. In this collection of 8 volumes the phrase attributed to the Greek engineer and physicist Archimedes is recorded, where he says, “give me a point of I will support and I will move the world ”, alluding to the great power that a lever could have if a sufficiently robust fulcrum were used.
The Greek historian Plutarch wrote in his book Parallel Lives that in a letter written by Archimedes to Hiero, the physicist explains to the king that he could move the planet and the monarch was so amazed that he asked for a demonstration. In this way, they carried out an experiment in which a ship of Hieron’s army, which had full holds and was in a dock, was loaded with numerous passengers and Archimedes, seated at a certain distance, managed to lift the ship out of the water without greater effort, using only a lever system.
As we can see, the lever is not only a machine that allows increasing mechanical strength, but it also has a very interesting history, and even today we use it in its different variants to perform tasks of different levels of complexity.