What does kinematics study? Concepts, quantities and task

What does kinematics study? With this question, students of the seventh classes almost immediately encounter, just starting the study of physics. Today we will talk about what the kinematics is studying, what concepts are most important in it. Let us consider the cases and the basics of this section of physics, we will understand what formulas can be used in it and in what cases it should be done.

What does mechanics, kinematics, dynamics study?

First of all, let's draw, so to speak, the demarcation lines between these three concepts. Mechanics is one of the physical sections. About it you can say that the mechanics itself is studying the laws of moving bodies. But the reader can find similar definitions even when it comes to kinematics with dynamics.

So what's the difference?

Let's try to understand first with what the kinematics is studying and what this science is. In fact, kinematics has never been independent. It is nothing but a section of mechanics. There are only three of them: kinematics, dynamics and statics. All these three sections are equally related to the mechanical category, that is, they study the interactions of bodies and the features of their displacement. However, each of them has characteristic features.

The subtleties of these sections

Kinematics, probably, is the most interesting section from the point of view of solving problems. A huge number of combinatorial solutions, really a huge space for their planning - all this becomes the cornerstones on which the popularity of kinematics is based. By the way, having opened even tests to prepare for the exam in 9th grade, we can immediately stumble upon simple examples. Speaking of what Kinematics is studying, we can mention that it considers the features of the motion of bodies without taking into account the forces of interactions.

A little more complicated is the situation with such a section of mechanics as dynamics. It also considers the motion of bodies and the corresponding quantities appear. This, for example, speed, distance, time. But a number of third-party terms also appear. Here the simple laws of motion do not get off, you will have to consider the mechanical system taking into account the forces acting on this or that body. But statics is already studying the rules of equilibrium in mechanical systems. There are not just bodies, but levers and other elements.

What is the basis of kinematics?

So, we found out that kinematics studies the motion of bodies without regard for the forces that act on the material points. But what was the basis of this section of mechanics, besides the basic laws? Concepts and definitions are, of course, good, but we can not use one theory to solve problems. At least, to achieve a positive or final result, we will have to resort to formulas. And in order to do this, first we will understand the values that will appear in them.

The basic quantities used in problems in kinematics

To begin with, we want to remind readers that they can have an extraordinary character. Let's start with a simple value, which we call distance. This is a scalar quantity. That is, having only a certain value. Three meters, which rolled the ball. 25 meters, which sailed the athlete. Ten kilometers, traveled by man for the whole day. All these are numerical values of the quantity, which we call distance.

A little bit different with the speed and acceleration, which in kinematics (and indeed in general) have a dual nature. On the one hand, we can give speed a numerical value. Let it be five, ten, twenty meters per second. But in fact speed has direction. It coincides with the direction of movement of the body, it is obvious. The same is true with acceleration. However, the speed and acceleration can be directed in different directions. In this case, the body will slow down. Imagine that the car is just starting to go, with every second gaining speed. Thus speed and acceleration are directed in one direction, due to what the speed of a body increases with each second. But when braking occurs, the vectors become directed in different directions.

Kinematics is a section of mechanics that studies the motion of bodies. But what can be the study if we do not use time intervals for this? Here it is - another value used to solve problems and describe the laws in this section of physics. It, along with distance, acceleration and speed, is included in some formulas most often used to bring solutions. Let's consider a fairly simple task on this topic, in order to finally consolidate in practice the theory obtained earlier in the course of the article.

A task

To test the characteristics of the car, a hundred-meter length of the ideal road is selected. It is known that its acceleration is equal to five meters per second in a square. Find out how long the car can go through the specified distance, taking into account that the movement starts from a state of rest.

So, since kinematics is a section of mechanics that studies the laws of motion of bodies, we will use the corresponding formulas. In the general case, it looks like this: S = V _o T + (-) (at ^ 2) / 2. But for our task we will change the form. It is said that movement begins from a state of rest. Hence, the initial velocity is zero. Consequently, the product of the velocity for a time V _o T will be zero. Once the car accelerates, a "+" sign is inherent in the formula. As a result, it takes the following form: S = (at ^ 2) / 2.

Next, we express the square of time. For this, we multiply both sides of the resulting equation by two to rewrite it. Now let's divide the doubled distance into acceleration. The last step for the expression will be the extraction of the square root from this expression. Well, we have simplified the formula as much as possible. Now it looks like this: T = sqrt (2S / a). It remains only to substitute the numbers. As a result, we get that the car has passed this distance for a time equal to about 6.32 seconds.