We explain what a lever is, the forces it uses and the variables to consider. Also, lever types and examples.
What is a lever?
A lever is a simple machine, that is, a device capable of modifying or generating a force and transmitting displacement. It is composed of a rigid bar made 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, increasing its speed or the distance it travels, through the application of a proportionally smaller amount of force.
Depending on the proximity or distance of the fulcrum from 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 to 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 motors.
- Resistance (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 exerted on it by the lever.
- Support force It is the force that the fulcrum exerts on the lever, equal and opposite to the previous two, since the bar is supported without moving on 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 the 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 x bp = R x Brthe power through your arm is equal to the resistance through yours.
The lever was invented in prehistory and there are records already in Mesopotamian antiquity of its use for irrigation swans. The first written mention of a lever comes from Pappus of Alexandria in his Mathematical Collection (340), where the famous quote from the Greek Archimedes appears: “Give me a lever and I will move the world.”
See also: Pulley
Lever types
There are three types of lever, depending on the relative position of the point of resistance, the power point and the fulcrum. Each one has different characteristics and will have a relatively different effect.
- First grade lever The fulcrum is between power and resistance, ensuring that the applied power can be much less than the resistance to overcome, that is, it maximizes the power. However, the speed transmitted 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 or distance traveled (but the energy savings are extremely useful).
- Third degree lever The power exerted is between the support point, at one end, and the resistance, at the other. The applied force is greater than the resulting one, but the transmitted speed or the distance traveled by the body is increased.
Examples of lever
Some everyday examples of leverage can be:
- First grade The rocker, the scissors, the tongs, the pliers, the catapults.
- Second grade The wheelbarrow, the nutcracker, a rowboat, a nursing stretcher, a lifting exercise machine.
- Third grade A fishing rod, a staple remover, an eyebrow tweezer or the temporomandibular joint of the human body.