Possessing the initial data, for any moving body it is possible to calculate the value of its acceleration, speed, location (coordinates), etc. All such calculations are performed within the framework of kinematics. However, this branch of science does not study the processes themselves arising from mechanical displacement. To answer questions about the characteristics of motion, the reason for the acceleration pulse can dynamics.
Take the boxes with one match inside and start moving it around the table in the same direction at the same speed. What happens to a match? Does she rest or move? It all depends on which frame of reference we choose. In relation to the box, the match is at rest, but if you look at what is happening from the side (for example, of the same table), it moves. The common thing in both cases is that the speed of the match is constant. To change it, it is necessary to exert external influence on the box and match, for example, push it off the table. This is what characterizes inertial reference systems. Suppose we are in a box next to a match. Since the external influence is not obvious, then at the time of the fall you might think that the match itself began to move, acquiring an acceleration impulse. But if you look at what is happening on the table, the behavior of the match is easily explained by the change in the speed of the box. In fact, we have described inertial and non-inertial reference systems. For the former, the action of external forces is characteristic, and for the latter, the acceleration obtained by external forces cannot be explained. In this example, inertial reference systems are connected to the surface of the table and any other object outside the box, since the external influence on the object under study is obvious. The problem of reference systems was interested in such prominent scholars of antiquity as Galileo and Aristotle. Only in the 17th century I. Newton on the basis of their work formulated his first rule of inertia, better known as the First Law of Newton.
It states that the existence of reference systems is permissible under which the body is not exerted by external influences from other bodies, and the speed of movement does not change either in value or in direction. If there are several influences, but they are balanced, then the same rule applies that inertial reference systems (ISO) use. If we consider one reference frame relative to another, with the modulus and value of the speed being constant, then we can say that in nature there is a huge amount of ISO. Therefore, inertial reference systems surround us everywhere.
It is much easier to understand Newton’s First Law if you look at the conclusions of his predecessors, Aristotle and Galileo.
Aristotle argued that if the body does not have any external influence, then his natural state is peace. If the body moves at a constant speed, an external force must be present.
Galileo supplemented these conclusions: the absence of external influence does not mean at all that the body cannot move uniformly and without changing direction. The force itself, which exerts an effect, is wasted on compensation for attraction, friction, etc.
The inertial system is completely based on the First Law, according to which any body rests or moves uniformly until an external force changes its state. An important feature: this law can not be implemented in all possible reference systems.
The inertial system is brilliantly confirmed and is actively used in celestial mechanics and astronautics (heliocentric system). It should be noted that there is no such frame of reference that would be inertial for all possible processes of the system in question.