Newton's first law

A significant number of discoveries in the field of physics were committed hundreds of years ago, surprisingly, without losing relevance to this day. And if the positions of molecular and quantum physics continue to be supplemented, and the scientific sections themselves develop, then mechanics is unlikely to discover something new.

Everyone knows that mechanics, as a branch of physics, is divided into dynamics and kinematics. At the same time, kinematics describes and studies the movement itself , and dynamics - the causes of its occurrence.

The main postulates explaining the reasons for the emergence and continuation of motion, to this day are rightfully considered the laws of Newton's dynamics, whose contribution to the development of this section of physics is difficult to overestimate. It was he who introduced such concepts as "mass", "inertia", "time" and many others. However, Isaac Newton is best known for his Laws, which allow us to describe the movement and principles of the interaction of bodies.

One of its main laws is called the Law of Inertia, or Newton's First Law. Its formulation proclaims the existence of such frames of reference, with respect to which the velocity of the body remains constant and does not change, if other fields or bodies do not act on it. Two conclusions can be drawn from this: first, in order for the body to change the trajectory of motion, so that it generally changes its position, and even to maintain its position, some force must be applied. In itself, the glass from the table does not come off: it must either be taken, or pushed, or shaken the table. However, without additional impact, the glass on the table will continue its straight-line movement at a constant speed. Why? Is it worth it?

Here we come close to the second conclusion, which allows us to make Newton's First law. One and the same body can both be in motion at the same time and remain at rest. The only question is in which frame of reference to consider one or another of its state. The same example with a glass: the glass is stationary relative to the table, relative to the observer - also. In general, relative to any frame of reference associated with the Earth, the glass in this example will remain stationary. However, we expand the angle of view: with respect to the bird flying over the glass, it will continue to move in a straight line with the speed of the Earth's motion. A bird, strictly speaking, in the situation of flight does not belong to the reference system Earth. A more indisputable situation, but no more vivid: the movement of the glass relative to Jupiter. The glass moves relative to the reference system of Jupiter, because Moves with the speed of the Earth. And in its frame of reference it is motionless.

Scientifically, the conclusion that Newton's First Law allows us to make is as follows: the reference frame, with respect to which the body moves rectilinearly and uniformly in the absence of external influences, is called inertial reference frames. In the situation described above, the inertial frame of reference for the glass will be a table. However, he is on the floor, the floor is in the house, the house is on the Earth. Generally speaking, all reference frames associated with the Earth are considered inertial. There is, however, a small caveat: due to the fact that the Earth rotates around its axis, completely Newton's first law can not be fulfilled. The falling body, strictly speaking, falls not vertically (its trajectory does not correspond to a straight line), but with a slight deviation to the east. However, such "deviations" in modern physics have been neglected to simplify calculations.

Having understood all the above, one can easily understand the statement that everything is in motion and everything is relative. The state of rest means not the absence of movement, but the exact opposite - straight uniform motion with constant speed.