What is kinematics? It is a subfield of mechanics that studies the mathematical and geometric methods of describing the motion of idealized objects. They fall into several categories. The topic of today's article will be aspects that are somehow related to the concept of "point kinematics". We will cover many topics, but we will start with the most fundamental concepts and explanations of their application in this area.
What objects are considered?
If kinematics is a branch of physics that studies how to describe the motion of bodies in spaces of different sizes, then you need to operate with the bodies themselves, right? To quickly understand what is at stake, you can find a multimedia lesson designed for students. Kinematics is generally simple to understand, if you understand its basics. When you get acquainted with them, you will notice that the theory contains information that this branch of physics studies the laws of motion of material objects.points. Notice how the definition of objects is generalized. On the other hand, material points are not the only objects considered by kinematics. This branch of physics studies the principles of motion of both absolutely rigid bodies and ideal fluids. Very often all these three concepts are combined into one, simply saying "idealized objects". Idealization in this case is needed for the conventions of calculations and the departure from possible systematic errors. If you look at the definition of a material point, you will notice that the following is written about it: this is a body whose dimensions can be neglected in the corresponding situation. This can be understood as follows: compared to the distance traveled, the linear dimensions of the object are negligible.
What is used to describe?
As mentioned earlier, kinematics is a subsection of mechanics that studies how to describe the motion of a point. But if this is so, does it mean that some fundamental concepts and principles, like axiomatic ones, are needed to perform such operations? Yes. And in our case, they are. First, in kinematics it is a rule to solve problems without looking back at the forces acting on a material point. We all know perfectly well that a body will accelerate or slow down if a certain force acts on it. And kinematics is the subsection that allows you to operate with acceleration. However, the nature of the emerging forces is not considered here. To describe the movement, methods of mathematical analysis, linear and spatial geometry are used, andalso algebra. Coordinate grids and the coordinates themselves also play a certain role. But we will talk about this a little later.
History of Creation
The first works on kinematics were compiled by the great scientist Aristotle. It was he who formed some of the fundamental principles of this industry. And even though his works and conclusions contained a number of erroneous opinions and reflections, his works are still of great value for modern physics. Aristotle's works were subsequently studied by Galileo Galilei. He carried out the famous experiments with the Leaning Tower of Pisa, when he investigated the laws of the process of free fall of a body. Having studied everything inside and out, Galileo subjected Aristotle's reflections and conclusions to harsh criticism. For example, if the latter wrote that force is the cause of motion, Galileo proved that force is the cause of acceleration, but not that the body will pick up and start moving and move. According to Aristotle, a body could acquire speed only when subjected to a certain force. But we know that this opinion is erroneous, since there is a uniform translational motion. This is once again proved by the formulas of kinematics. And we'll move on to the next question.
Kinematics. Physics. Basic concepts
There are a number of fundamental principles and definitions in this section. Let's start with the main one.
Mechanical movement
Probably, from the school bench we are trying to lay the idea of what can be considered a mechanical movement. We deal with it daily, hourly, every second. We will consider mechanical motion a process that occurs in space over time, namely, a change in the position of a body. At the same time, relativity is often applied to the process, that is, they say that the position of, say, the first body has changed in relation to the position of the second. Let's imagine that we have two cars at the starting line. The go-ahead of the operator or the lights lit up - and the cars take off. At the very beginning there is already a change of position. Moreover, you can talk about this for a long time and tediously: regarding a competitor, regarding the start line, regarding a fixed spectator. But perhaps the idea is clear. The same can be said about two people who go either in one direction or in different directions. The position of each of them relative to the other changes at each moment of time.
Reference system
Kinematics, physics - all these sciences use such a fundamental concept as frames of reference. In fact, it plays a very important role and is used in practical problems almost everywhere. Two more important components can be connected with the frame of reference.
Coordinate grid and coordinates
The latter are nothing more than a collection of numbers and letters. Using certain logical settings, we can compose our owna one-dimensional or two-dimensional coordinate grid, which will allow us to solve the simplest problems of changing the position of a material point over a given period of time. Usually, in practice, a two-dimensional coordinate grid is used with the axes X ("x") and Y ("y"). In three-dimensional space, it adds the Z axis (“z”), and in one-dimensional space, only X is present. Artillerymen and scouts often work with coordinates. And for the first time we encounter them in elementary school, when we begin to draw segments of a certain length. After all, graduation is nothing more than the use of coordinates to indicate the beginning and end.
Kinematics Grade 10. Quantities
The main quantities used in solving problems on the kinematics of a material point are distance, time, speed and acceleration. Let's talk about the last two in more detail. Both of these quantities are vector. In other words, they have not only a numerical indicator, but also a certain predetermined direction. The movement of the body will occur in the direction in which the velocity vector is directed. At the same time, one should not forget about the acceleration vector if we have a case of uneven movement. Acceleration can be directed in the same direction or in the opposite direction. If they are co-directed, then the body will start moving faster and faster. If they are opposite, then the object will slow down until it stops. After that, in the presence of acceleration, the body will acquire the opposite speed, that is, it will move in the opposite direction. All this in practice is very, very clearly shown by kinematics. 10th grade is just thatthe period when this section of physics is sufficiently disclosed.
Formulas
Kinematics formulas are quite simple both for output and for memorization. For example, the formula for the distance traveled by an object in a given time is as follows: S=VoT + aT^2/2. As we can see, on the left side we have just the same distance. On the right side, you can find the initial speed, time and acceleration. The plus sign is only conditional, since acceleration can take a negative scalar value during the process of object deceleration. In general, the kinematics of motion implies the existence of one type of speed, we constantly say “initial”, “final”, “instantaneous”. Instantaneous speed appears at a certain point in time. But after all, if you think so, then the final or initial components are nothing but its particular manifestations, right? The topic "Kinematics" is probably a favorite among schoolchildren, because it is simple and interesting.
Examples of problems
In the simplest kinematics, there are whole categories of very different tasks. All of them are connected in one way or another with the movement of a material point. For example, in some it is required to determine the distance traveled by the body in a certain time. In this case, parameters such as initial velocity and acceleration can be known. Or maybe the student will be given a task, which will just consist in the need to express and calculate the acceleration of the body. Let's take an example. The car starts from a static position. What distance will he have time to cover in 5 seconds if his acceleration is three meters,divided by a second squared?
To solve this problem, we need the formula S=VoT + at^2/2. We simply substitute the available data into it. It's acceleration and time. Note that the term Vot will go to zero, since the initial velocity is zero. Thus, we get a numerical answer of 75 meters. That's it, problem solved.
Results
Thus, we figured out the fundamental principles and definitions, gave an example of a formula and talked about the history of the creation of this subsection. Kinematics, the concept of which is introduced in the seventh grade in physics lessons, continues to be constantly improved within the framework of the relativistic (non-classical) section.
