The word inertia derives from the Latin "inertĭa" means "incapacity, inability, inaction, laziness, laziness", it is composed of the components of the prefix "in" which is "privative, negative" and "ars" is of "art, ability, disposition ”, in the dictionary of the real Spanish academy defines the word inertia as the “ property of bodies not to modify their state of rest or movements if it is not by the action of a force ”.
Inertia in physics is the membership that the corresponding bodies have in their state of rest or displacement, during the force is equal to zero or the resistance that matter opposes to modify its state of rest or displacement.
The inertia in Newton's first law is what says that a body at rest or in displacement, can be "uniform or rectilinear" that can belong to a state of rest or that it conserves its displacement quantitatively, if the forces acting from the exterior are equal to zero.
The forces of inertia is the vitality that the bodies opposing the displacement and the consequences of their mass that is determined at the moment of inertia of a material point with the link of an axis, the product of the mass of this point by the square of its distance from the axis. But it is a method, linked to an axis, the moment of inertia is the method that is similar to the sum of the opportunities of inertia of all the material points that comprise it.
