We explain what a lever is, the forces it uses and the variables to consider. In addition, lever types and examples.
What is a lever?
By lever we refer to a simple machine, that is, to a device capable of modifying or generating a force and transmitting displacement , composed of a rigid bar of some moderately resistant material, which rotates freely on a fulcrum called fulcrum.
A lever can be used to maximize the mechanical force applied to an object, increase its speed or the distance it travels, by applying a proportionately smaller amount of force.
Thus, depending on the proximity or distance of the fulcrum with respect to the body to be moved, more or less applied force will be required and a greater or lesser effect will be achieved.
Three forces act simultaneously on a lever:
- Power (P) : The force applied voluntarily at the end of the lever, with the desire to generate a reaction. It can be run manually or by a weight , or even electric or steam engines.
- Resistance (R) : The force to be overcome by the power, that is, the weight exerted on the lever by the body we wish to move and which will be equivalent, by the Law of action and reaction, to which the lever exerts on it.
- Support force: The force exerted by the fulcrum on the lever, opposite to the previous two, since the bar is held without moving on the support point.
In turn, there are two other variables to consider in the case:
- Power arm ( B p ) : This is called the distance between the fulcrum and the power application point.
- Resistance arm (Br) : Logically, it is the distance between the fulcrum and the load or the body to be mobilized.
All of the above is related through the following formula:
P x Bp = R x Br , the power on his arm is equal to the resistance on his.
The lever was invented in human prehistory , and there are records already in Mesopotamian antiquity of its use for irrigation crankshafts. The first written mention of a lever comes from Pappus of Alexandria in his Mathematical Collection (340), where the famous quotation of the Greek Archimedes appears: “Give me a lever and I will move into the world.”
There are three types of lever, depending on the relative position of the resistance point, the power point and the fulcrum. Each has different characteristics and will have a relatively different effect.
- First degree lever . The fulcrum is between the power and the resistance, achieving that the applied power can be much less than the resistance to be overcome, that is, maximizes the power. However, the transmitted speed and the distance traveled by the body would be sacrificed.
- Second grade lever . The resistance is between the power and the fulcrum, so the power will always be less than the resistance, even if it does not achieve greater displacement or distance traveled. But such energy saving is extremely useful.
- Third grade lever . The power exerted lies between the point of support, on one end, and the resistance, on the other. The force applied, thus, is greater than the resultant (decreases), but it is possible to extend the transmitted speed or the distance traveled by the body.
Some everyday examples of lever can be:
- First grade : the rocker, the scissors, the pliers, the pliers, the catapults with which castles were besieged in the Middle Ages.
- Second grade : the wheelbarrow, the nutcracker, a rowing boat, a nursing table, an exercise machine by lifting.
- Third grade : a fishing rod, a staple remover, an eyebrow clamp or the temporomandibular joint of the human body.