What is kinematics? High school students first begin to get acquainted with its definition in physics classes. Mechanics (kinematics is one of its sections) itself makes up most of this science. Usually it is presented to students first in textbooks. As we said, kinematics is a subsection of mechanics. But since we are talking about her, we’ll talk about this in more detail.
Mechanics as part of physics
The very word “mechanics” is of Greek origin and is literally translated as the art of building machines. In physics, it is considered a section that studies the movement of the so-called material bodies in different-sized spaces (that is, the movement can occur in one plane, on a conditional coordinate grid or in three-dimensional space). The study of the interaction between material points is one of the tasks that mechanics performs (kinematics is an exception to this rule, since it is engaged in modeling and analysis of alternative situations without taking into account the influence of force parameters). For all this, it should be noted that the corresponding section of physics means by motion a change in the position of the body in space over time. This definition applies not only to material points or bodies in general, but also to their parts.
Kinematics concept
The name of this section of physics is also of Greek origin and is literally translated as “move”. Thus, we get an initial, not yet truly formed answer to the question of what kinematics is. In this case, we can say that the section studies mathematical methods for describing various types of motion of directly idealized bodies. We are talking about the so-called absolutely solid bodies, about ideal fluids, and, of course, about material points. It is very important to remember that when applying the description, the causes of movement are not taken into account. That is, such parameters as body weight or force, which affects the nature of its movement, are not subject to consideration.
Kinematics basics
They include concepts such as time and space. As one of the simplest examples, we can cite a situation where, for example, a material point moves along a circle of a certain radius. In this case, kinematics will attribute the obligatory existence of such a quantity as centripetal acceleration, which is directed along the vector from the body itself to the center of the circle. That is, the acceleration vector at any time will coincide with the radius of the circle. But even in this case (in the presence of centripetal acceleration), kinematics will not indicate the nature of the force that caused it to appear. These are already the actions that the speaker takes apart.
What is kinematics?
So, the answer to what kinematics is, in fact, we gave. It is a branch of mechanics that studies methods for describing the motion of idealized objects without studying the force parameters. Now let's talk about what kinematics can be. Its first type is classical. It is generally accepted in it that the spatial and temporal characteristics of a certain type of movement are considered absolute. In the role of the former appear the lengths of segments, in the role of the latter - time intervals. In other words, we can say that these parameters remain independent of the choice of the reference frame.
Relativistic
The second type of kinematics is relativistic. In it, between two corresponding events, the temporal and spatial characteristics can change if there is a transition from one reference frame to another. The simultaneity of the origin of two events in this case also assumes an exclusively relative character. In this kind of kinematics, two separate concepts (and we are talking about space and time) merge into one. In it, the value, which is usually called the interval, becomes invariant with respect to the Lorentz transformations.
The history of the creation of kinematics
We were able to deal with the concept and give an answer to the question of what kinematics is. But what was the history of its occurrence as a subsection of mechanics? This is what we should talk about now. For quite some time, all the concepts of this subsection were based on works that were written by Aristotle himself. In them there were relevant statements that the speed of a body during a fall is directly proportional to the numerical indicator of the weight of a body. It was also mentioned that the cause of the movement is directly the force, and in its absence there can be no question of any movement.
The experiences of Galileo
The work of Aristotle in the late sixteenth century became interested in the famous scientist Galileo Galilei. He began to study the process of free fall of the body. We can mention his experiments that he conducted on the Leaning Tower of Pisa. The scientist also studied the process of inertia of bodies. In the end, Galileo managed to prove that Aristotle was wrong in his work, and he made a number of erroneous conclusions. In the corresponding book, Galileo outlined the results of work with evidence of the fallacy of Aristotle's conclusions.
Modern kinematics, as it is believed today, originated in January 1700. Then Pierre Varignon addressed the French Academy of Sciences. He cited the first concepts of acceleration and speed, writing and explaining them in a differential form. A little later, Ampere took note of some kinematic ideas. In the eighteenth century, he used the so-called calculus of variations in kinematics. The special theory of relativity, created even later, showed that space, like time, is not absolute. At the same time, it was indicated that the speed can be fundamentally limited. It was such foundations that pushed kinematics to development within the framework and concepts of the so-called relativistic mechanics.
The concepts and values used in the section
The basics of kinematics include several quantities that are used not only in theoretical terms, but also take place in practical formulas used in modeling and solving a certain range of problems. We will get acquainted with these quantities and concepts in more detail. Let's start with the latter.
1) Mechanical movement. It is defined as changes in the spatial position of a certain idealized body relative to others (material points) during a change in the time interval. In this case, the bodies that are mentioned have corresponding interaction forces among themselves.
2) The reference system. Kinematics, the definition of which we gave earlier, is based on the use of a coordinate system. The presence of its variations is one of the necessary conditions (the second condition is the use of instruments or means for measuring time). In general, a frame of reference is necessary for the successful description of a particular type of movement.
3) Coordinates. Being a conditional imaginary indicator, inextricably linked with the previous concept (reference system), the coordinates are nothing more than a way by which the position of an idealized body in space is determined. At the same time, numbers and special characters can be used for the description. Coordinates are often used by scouts and gunners.
4) Radius vector. This is a physical quantity that is used in practice to set the position of an idealized body with an eye on the initial position (and not only). Simply put, a certain point is taken and it is fixed for convention. Most often this is the origin. So, after this, let’s say, an idealized body from this point starts moving along a free arbitrary trajectory. At any moment of time, we can connect the position of the body with the origin, and the resulting line will be nothing more than a radius vector.
5) The kinematics section uses the concept of a trajectory. It is an ordinary continuous line, which is created during the movement of an idealized body with arbitrary free movement in different sizes. The trajectory, respectively, can be rectilinear, circular and broken.
6) The kinematics of the body are inextricably linked to such a physical quantity as speed. In fact, this is a vector quantity (it is very important to remember that the concept of a scalar quantity is applicable to it only in exceptional situations), which will give a characteristic of the rate of change in the position of an idealized body. It is considered to be vectorial due to the fact that the speed sets the direction of the ongoing movement. To use the concept, it is necessary to use a frame of reference, as mentioned earlier.
7) Kinematics, the definition of which tells us that it does not consider the causes of motion, in certain situations it also considers acceleration. It is also a vector quantity that shows how intensively the velocity vector of the idealized body will change with an alternative (parallel) change in the unit of time. Knowing at the same time in which direction both vectors are directed - speed and acceleration - we can say what kind of motion the body has. It can be either equally accelerated (the vectors coincide) or equally slow (the vectors are multidirectional).
8) Angular velocity. Another vector quantity. In principle, its definition is the same as that given earlier. In fact, the only difference is that the previously considered case occurred when moving along a rectilinear trajectory. Here we have a circular motion. It can be a neat circle, as well as an ellipse. A similar concept is given for angular acceleration.
Physics. Kinematics. Formulas
To solve practical problems associated with the kinematics of idealized bodies, there is a whole list of very different formulas. They allow you to determine the distance traveled, instantaneous, initial final speed, the time during which the body has passed this or that distance, and much more. A separate application (particular) is the situation with a simulated free fall of the body. In them, the acceleration (indicated by the letter a) is replaced by the acceleration of gravity (the letter g, numerically equal to 9.8 m / s ^ 2).
So what did we find out? Physics - kinematics (the formulas of which are derived one from the other) - of this section is used to describe the motion of idealized bodies without taking into account the force parameters that become the causes of the corresponding motion. The reader can always familiarize himself with this topic in more detail. Physics (the topic of “kinematics") is very important, since it is it that gives the basic concepts of mechanics as a global section of the corresponding science.