In the field of physics there are many important terms that must be taken into account and analyzed. One of them is inertia , a property that bodies have and comes from the Latin word “ inertĭa ” which means incapacity, inaction or inability. This term is used to refer to the ability of bodies to avoid the change in states of rest or motion unless a force acts on them.




I = Σ m i * r i ²


What is inertia?

Inertia is known as the resistance capacity that bodies have to change their state of rest or movement , either to modify speed or direction . It is a term also used to refer to modifications of the physical state of a body.

  • Meaning
  • Inertia characteristics
  • History
  • Types
  • Moment of inertia
  • How it is calculated
  • Interpretations
  • Applications
  • Importance
  • Examples


The word inertia refers to the ability of a certain body to be able to maintain its state of rest or relative movement . It is a resistance that a body exerts to the changes that occur in terms of direction or speed. This resistance exerted by the object before the change of direction or movement is also known as the inertial force.

Inertia characteristics

Among the main characteristics of inertia, the following are mentioned:

  • It is a fundamental property of matter.
  • It is seen as the tendency of bodies to maintain their state of rest .
  • It can only occur when a certain body is subjected to the action of a force .
  • It gives the bodies the ability to maintain the state of relative rest as long as no type of force is exerted that can vary the state.
  • It is seen as a type of resistance .
  • It is an important part of Newton’s First Law also known as the Law of Inertia.


The history of inertia begins in ancient times and was an aspiration that all scientists and philosophers of the time had. The first study to be done regarding the movement was done by Aristotle and it was later improved and remodeled by the Arabs in the 11th century. The first scholastics made several criticisms of the theory and the thinkers of the Renaissance established the foundations for Kepler, Galileo, Descartes and Huygens to delve into the subject later.

In this story, Aristotle was the founder of physics as a science and studied the movement and change of bodies as a basic part of nature. His studies rejected the void and also referred to the resistance of the movement , however, it also had its cons and the theory was improved over the years.


There are several types of inertia, among which we mention the following:

  • Thermal inertia : this type of inertia refers to the ability of a certain body to be able to make changes in its temperature when it comes into contact with other objects or when it is subjected to heat.
  • Mechanical inertia : it is the difficulty that occurs at the moment of modifying the movements and the state of stillness . This type of inertia will always depend on the amount of mass that the body has and the inertia tensor. In this type of inertia there is also a subdivision:
  • Static inertia : it occurs in those objects or bodies that are in a state of relative rest.
  • Translational inertia : it is closely related to the amount of mass that bodies have.
  • Rotational inertia : it is found in those bodies that have a type of rotational movement.

Moment of inertia

The moment of inertia is a term used in the field of physics . The word moment refers to the amount of movement that a body presents, it is the magnitude that results from the multiplication of the speed by the mass that a body has. Inertia, on the other hand, is a property that objects have to be able to maintain their state either of motion or of rest until a certain force acts on it.

In this way we can say that the moment of inertia is the sum of the products that result from multiplying the mass of the objects by the square of the distance it has towards the axis of rotation. It is closely linked to the way in which the mass of a body is distributed with respect to a certain axis of rotation .

How it is calculated

The formula used to calculate the moment of inertia is the following:

I = Σ m i * r i ²


  • I : is the moment of inertia itself
  • M : refers to the mass of the particles
  • R : is the minimum distance that exists between the axis and the particle
  • Symbol Σ: known as summation and is a notation used to denote the sum of several terms that are expressly delimited.


Several scientists and researchers see inertia as a manifestation of mass and some see it as a characteristic of mass . This term has been stable for many years, as currently few researchers have managed to contribute new ideas to the term of inertia.


There are several fields in which the law of inertia applies. It is common to observe it in the field of aerodynamics , in the area of biomechanics and in the calculation of deflections to be able to determine by means of it the degree of resistance to bending that certain materials have. It is also an important part of the area of kinematics, mainly that which is related to the angular movement of objects and can also be used to determine in an adequate way the resistance of the different materials used in construction and in structural design. .


Inertia is a very important property especially in the field of statics and dynamics . It is considered on many occasions as a parameter of vital importance to be able to calculate the stress in the different structures. It is also a fundamental part of the law of inertia , one of the first laws that were postulated by Isaac Newton .


Some examples of inertia are as follows:

  • The seat belts are in a car. While the vehicle is kept at a constant speed, the passengers will also maintain a constant speed, however, when the car stops abruptly, the passengers will be pushed forward causing the seat belt to interrupt the inertial movement and prevent it from collide with the passenger against the windshield .
  • When an object that is heavy and that was at rest is pushed , a great force is needed to be able to overcome the inertial force of the object, after this force is broken, the object can be displaced more easily.
  • Constructions using adobe which is a material that has a large amount of thermal inertia so it becomes a heat resistant material making the house stay cooler.

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