What is kinematics? For the first time, secondary school students begin to get acquainted with its definition in physics lessons. Mechanics (kinematics is one of its branches) itself constitutes a large part 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, let's talk about this in a little more detail.
Mechanics as part of physics
The word “mechanics” itself is of Greek origin and literally translates as the art of building machines. In physics, it is considered a section that studies the movement of the so-called material bodies by us 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 analyzing alternative situations without taking into account the impact of force parameters). With all this, it should be noted that the corresponding branch of physicsmeans by movement the change in the position of the body in space over time. This definition is applicable not only to material points or bodies as a whole, but also to their parts.
The concept of kinematics
The name of this section of physics is also of Greek origin and literally translates as “move”. Thus, we get the 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 certain types of motion of directly idealized bodies. We are talking about the so-called absolutely solid bodies, about ideal liquids, 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, parameters such as body mass or force that affect the nature of its movement are not subject to consideration.
Fundamentals of kinematics
They include concepts such as time and space. As one of the simplest examples, we can cite a situation where, say, 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 (withcentripetal acceleration) kinematics will not indicate the nature of the force that caused it to appear. These are already actions that the dynamics parses.
What is kinematics like?
So, we, in fact, gave the answer to what kinematics is. It is a branch of mechanics that studies how to describe the motion of idealized objects without studying force parameters. Now let's talk about what kinematics can be. Its first type is classical. It is customary to consider the absolute spatial and temporal characteristics of a certain type of movement. In the role of the former, the lengths of the segments appear, in the role of the latter, the time intervals. In other words, we can say that these parameters remain independent of the choice of reference system.
Relativistic
The second type of kinematics is relativistic. In it, between two corresponding events, temporal and spatial characteristics can change if a transition is made from one frame of reference to another. The simultaneity of the origin of two events in this case also takes on 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 quantity, which is usually called the interval, becomes invariant under Lorentzian transformations.
The history of the creation of kinematics
Usmanaged to understand the concept and give an answer to the question of what kinematics is. But what was the history of its emergence as a subsection of mechanics? This is what we need to talk about now. For quite a long time, all the concepts of this subsection were based on works that were written by Aristotle himself. They contained relevant statements that the speed of a body during a fall is directly proportional to the numerical indicator of the weight of a particular body. It was also mentioned that the cause of the movement is directly the force, and in its absence, there can be no talk of any movement.
Experiments of Galileo
The famous scientist Galileo Galilei became interested in the works of Aristotle at the end of the sixteenth century. He began to study the process of free fall of the body. Mention may be made of his experiments 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 works, and he made a number of erroneous conclusions. In the corresponding book, Galileo outlined the results of the work carried out with evidence of the fallacy of Aristotle's conclusions.
Modern kinematics is now considered to have originated in January 1700. Then Pierre Varignon spoke before the French Academy of Sciences. He also brought the first concepts of acceleration and speed, writing and explaining them in a differential form. A little later, Ampere also took note of some kinematic ideas. In the eighteenth century he used in kinematics the so-calledvariational calculus. The special theory of relativity, created even later, showed that space, like time, is not absolute. At the same time, it was pointed out that the speed could be fundamentally limited. It is these foundations that prompted kinematics to develop within the framework and concepts of the so-called relativistic mechanics.
Concepts and quantities 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. Let's get acquainted with these quantities and concepts in more detail. Let's start with the last ones.
1) Mechanical movement. It is defined as changes in the spatial position of a certain idealized body relative to others (material points) in the course of changing the time interval. At the same time, the bodies that are mentioned have the corresponding forces of interaction with each other.
2) Reference system. Kinematics, which we defined 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 one or another type of movement.
3) Coordinates. Being a conditional imaginary indicator, inextricably linked with the previous concept (frame of reference), the coordinates are nothing more than a method by which the position of an idealized body inspace. In this case, 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 to the original position (and not only). Simply put, a certain point is taken and it is fixed for convention. Most often this is the origin of coordinates. So, after that, let's say, an idealized body from this point begins to move along a free arbitrary trajectory. At any point in time, we can connect the position of the body to the origin, and the resulting straight 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 during arbitrary free movement in a space of different sizes. The trajectory, respectively, can be rectilinear, circular and broken.
6) The kinematics of the body is inextricably linked with 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 characterize the speed of change in the position of an idealized body. It is considered to be a vector due to the fact that the speed sets the direction of the ongoing movement. To use the concept, you must apply the frame of reference, as mentioned earlier.
7) Kinematics, the definition of which tells aboutthat it does not consider the causes that cause movement, in certain situations it also considers acceleration. It is also a vector quantity, which shows how intensively the velocity vector of an idealized body will change with an alternative (parallel) change in the unit of time. Knowing at the same time in which direction both vectors - speed and acceleration - are directed, we can say about the nature of the movement of the body. It can be either uniformly accelerated (the vectors are the same) or uniformly slow (the vectors are in opposite directions).
8) Angular velocity. Another vector quantity. In principle, its definition coincides with the analogous one that we gave 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 related to the kinematics of idealized bodies, there is a whole list of various formulas. They allow you to determine the distance traveled, the instantaneous, the initial final speed, the time during which the body has passed this or that distance, and much more. A separate case of application (private) are situations with a simulated free fall of a body. In them, acceleration (denoted by the letter a) is replaced by the acceleration of gravity (letter g, numerically equals 9.8 m/s^2).
So what did we find out? Physics - kinematics (the formulas of whichderived from one another) - 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 get acquainted with this topic in more detail. Physics (the topic “kinematics”) is very important, since it is it that gives the basic concepts of mechanics as a global section of the corresponding science.
