The Newton’s laws are three principles proposed by the English mathematician and physicist Isaac Newton (1643–1727). These postulates allow us to provide an answer to most of the problems that arise in the classical mechanics With respect to movement of the bodies.
The Newton’s first law is known as principle of inertia and points out that bodies do not change their state of motion or rest if a strength, or if the resultant of the applied forces is null.
In other words, according to the principle of inertia a body is kept in uniform line movement or in repose unless influenced by a force. Equilibrium appears when the resultant of the forces that affect it is zero.
From the principle of inertia it follows that bodies oppose the modification of their state of movement or rest. Inertia, in fact, is such opposition. It should be remembered, on the other hand, that a force is the agent that can generate a variation in the state of the object.
Ultimately, they need external forces for a body to abandon its uniform rectilinear motion or its rest. Therefore, without a push, a friction, friction, etc., the element in question will always maintain its constant speed, even when it is zero.
The principle of inertia reveals that, if we have a body at rest (without movement), it will never move unless a force is applied to it. A box, to cite one case, will only move if someone pushes it. A body that moves in a surface Without friction, on the other hand, it will keep its speed constant for infinite time, until it is forced to brake by frictional forces or some other mechanism.
While all of this works in the theory, it is practically impossible to reproduce it in reality, and much more to see examples spontaneously. This is because in nature we do not find perfectly smooth surfaces, without alterations that cause friction, nor means in which there is no wind or any other element that causes forces opposed to the movement of a body.
It is possible to elaborate a more formal definition of the principle of inertia, making use of the derivatives. Although it is a difficult concept to understand without an application, we can define it as the rate of change of a function that is expressed according to the variation of its value when its independent variable is modified, that is, the one on which another depends.
In the field of physics, we say that in order to know how a function given we can observe its derivative. In more precise terms, when affirming that the speed of a moving body remains constant in time because there are no external forces that affect it, then it is also true that the derivative of said speed in relation to time is zero, that is, it does not vary over time.
The concept of the principle of inertia can be related to the linear momentum. This is also known as momentum, momentum or momentum, and it is a vector that we can use to describe the movement of a body within the field of mechanics.
For the motion of a body has the linear momentum as one of its main characteristics, and through this concept a relationship is established between the mass of the body with its respective speed. If the mass of an isolated body remains constant throughout the process of motion, it is possible to say that its momentum is also constant. This is also known as principle of conservation of linear momentum.