Levers are simple machines capable of multiplying the force that is applied to a body or object when resting on a fixed point. There are three types of levers, which differ according to the points of force application:
The working principle of levers was described in the 3rd century BC by the philosopher Archimedes .
types of lever
Levers are rigid objects that can be used to move or hold bodies that are difficult to handle or even very heavy . According to their size and the points where the forces are applied, the levers are capable of promoting a great mechanical advantage, that is, multiplying the intensity of the force produced.
The mechanical advantage of levers directly depends on the distance between the point of application of the powerful force and the point of support. The greater this distance, commonly called an “arm”, the less effort required.
The physical quantity related to the effect produced by the levers is the moment of a force, also called torque . The moment of a force is a vector quantity that can be calculated using a mathematical operation known as cross product or cross product. To learn more about operations with vectors, visit our specific article: Vectors .
In all types of levers, there are at least three forces at work : the powerful force, the resisting force, and the normal force , which are, respectively, the force that tries to move the body, the weight of the body, and the force exerted on the body. support point.
There are three distinct types of lever:
- Interfixed levers : the fulcrum is between the points where the powerful force is applied and the point where the weight of the object to be moved is.
- Inter-resistant levers: the weight force is applied between the fulcrum and the powerful force.
- Interpotent lever: the point of application of the powerful force is located between the point of support and the point where the weight of the body to be moved acts.
xamples of levers
Levers come in different configurations and are used for different tasks, so it’s important to know some real-life examples of lever types.
- Interfixed levers : pliers, scissors and seesaws.
- Inter-resistant levers : nutcracker, bottle opener, wheelbarrow.
- Interpotent levers: tweezers, nail clippers.
- P – powerful force
- A – support point
- R – resisting force
Solved exercises on levers
Question 1 — (CFT-MG) The following illustration shows the displacement of the rowers in a lake, with the oars being considered levers.
A student, when analyzing this situation, on the shore of the lake, stated that
I. the lever is of the interfix type.
II. the fixed point of the lever is in the water.
III. the arm of the resisting force is smaller than that of the potent force.
IV. the force of the water on the boat is less than that exerted by the rowers.
Only the statements are correct
a) I and II.
b) I and IV.
c) II and III.
d) III and IV.
Let’s analyze the alternatives:
a) FALSE. The fulcrum is in the water.
c) FALSE. The “arm” of the powerful force is the distance between the point where the powerful force is applied on the paddle to the fulcrum, which, in this case, is in the water.
Based on the analysis of the alternatives, the correct answer is the letter C .
Question 2 — (Acafe) Basically, a lever is a bar that can rotate around a point of support, called a pole. Even in our body there are many levers, as there are many articulating parts.
In the following figure we see the example of three different types of levers: on the foot (1), on the arm/forearm (2) and on the head (3).
The correct alternative that shows in the sequence (1), (2) and (3) the classification according to the position of the support point in relation to the applied forces is:
a) interfix; interpotent and inter-resistant.
b) inter-resistant; interfixed and interpotent.
c) interpotent; interfixed and interresistant.
d) inter-resistant; interpotent and interfix.
As we know, inter-resistant levers are those in which the resistant force is applied between the fulcrum and the point of application of the powerful force, which can be seen in the first image. In the second image, where you can see the arm, you can see that the powerful force is applied between the points of support and the resistant force, so the only correct alternative is the letter D .