Speed is known by almost identical value in all spheres of science. In various sections of the physics there are several concepts of speed, each of which makes a certain general sense.
Mechanistic concept of speed of physics
The most widespread determination of speed in physics is its definition as speeds of the movement of a body. In this context the change of coordinate of position of a body in unit of time is considered. Thus, mild determination of speed of a body is a distance which overcomes a body per unit of time. However it is known that the speed of a body is measured not in meters, for example, and not in kilometers, and more likely in meters per second or kilometers per hour in spite of the fact that definition says that speed is a distance. The fact is that purely mathematically to find the distance passed by a body per unit of time it is necessary to divide the general distance passed by a body, for a while for which this distance was overcome. That is meters are divided into seconds. From here also such unit of measure turns out.
However the above-stated determination of speed as it was already told, mild. The fact is that in case for different periods the body passes different distances, division of the general distance into the general time will give only average speed. The instant value of speed means finding of derivative function of distance from time. Thus, for understanding of strict determination of speed of a body it is necessary to understand a mathematical definition of derivative function.
Speed in mathematics
The concept of speed of mathematics is connected with the speed of recession of any function in this point. And the speed of recession of function is defined by its derivative. If it is about the speed of the movement of a body, then the considered function is meant as the distance passed by a body. So, the derivative of function is a limit of the relation of increment of function to increment of an argument when increment of an argument tends to zero. Actually, this definition differs from mild determination of speed only in existence of a limit. Therefore to find exact value of speed of the movement of a body at present of time, it is necessary to divide a distance interval into the period corresponding to it, and after – to direct the period to zero, then the received value of the relation will give exact current value of speed.
Other concepts of speed of physics
Actually, as it was already told above, the speed of the movement of a body is only a special case in definition of a concept of speed. If to replace distance with any other physically reasonable size, then it will be possible to receive the speed of change of this size in unit of time.