We explain what a lever is, the forces it uses and the variables to consider. Also, the lever types and examples.
A lever is capable of modifying or generating a force and transmitting displacement.
What is a lever?
A lever is a simple machine, that is, a device capable of modifying or generating a force and transmit displacement. It is composed of a rigid bar of some moderately resistant material, which rotates freely on a support point called fulcrum.
A lever can be used to maximize the mechanical force applied to an object, increase its speed or the distance it travels, through the application of a proportionally less amount of force.
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). It is the force voluntarily applied at the end of the lever, in order to generate a reaction. It can be executed manually or by means of a weight, or even electric or steam engines.
- Endurance (R). It is 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 that which the lever exerts on it.
- Support force. It is the force exerted by the fulcrum on the lever, equal to and opposite to the previous two, since the bar is held without moving over the fulcrum.
In turn, there are two other variables to consider in the case:
- Power arm (Bp). It is the distance between the fulcrum and the point of application of power.
- Resistance arm (Br). It is the distance between the fulcrum and the load or body to be mobilized.
All of the above is related through the following formula:
P xBp = R x Br, the power per arm is equal to the endurance for yours.
The lever It was invented in the prehistory, and there are records already in Mesopotamian antiquity of its use for irrigation shafts. The first written mention of a lever comes from Pappus of Alexandria in hisMathematical collection , where the so famous quote of the Greek Archimedes appears: "Give me a lever and I will move the world."
In first degree levers, the fulcrum is between power and resistance.
There are three types of lever, depending on the relative position of the point of resistance, that of power and the fulcrum. Each one has different characteristics and will have a relatively different effect.
- First degree lever. The fulcrum is between power and resistance, achieving that the applied power can be much less than the resistance to overcome, that is, it maximizes power. However, the transmitted speed and the distance traveled by the body are sacrificed.
- Second degree 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 nor distance traveled (but saving Energy is extremely useful).
- Third degree lever. The power exerted is between the fulcrum, at one extreme, and the resistance, at the other. The applied force is greater than the resulting one, but it is possible to increase the transmitted speed or the distance traveled by the body.
Some everyday examples of toggle can be:
- First grade. The seesaw, the scissors, the pliers, the pliers, the catapults.
- Second grade. The wheelbarrow, the nutcracker, a rowing boat, a nursing gurney, a lifting machine.
- Third grade. A fishing rod, a staple remover, an eyebrow tweezers or the temporomandibular joint of the human body.