What does kinematics study? Pupils of the seventh grades almost immediately encounter this question, just starting the study of physics. Today we’ll talk about what kinematics is studying, what concepts are most important in it. Let us consider the cases and the fundamentals of this section of physics, we will understand what formulas can be used in it and in which cases this should be done.
What is studying mechanics, kinematics, dynamics?
First of all, let's draw, so to speak, demarcation lines between these three concepts. Mechanics is one of the physical sections. We can say about it that mechanics itself is studying the laws of the movement of bodies. But the reader can come across similar definitions when it comes to kinematics with dynamics.
So what is the difference?
Let's first try to understand what 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 three of them: kinematics, dynamics and statics. All these three sections relate equally to the mechanical category, that is, they study the interactions of bodies and the features of their movement. However, each of them has characteristic features.
The subtleties of these sections
Kinematics is probably the most interesting section in terms of solving problems. A huge number of combinatorial solutions, really huge scope for their planning - all this becomes the cornerstones on which the popularity of kinematics is based. By the way, even opening tests to prepare for the exam in the 9th grade, we can immediately come across simple examples. Speaking about 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 bit more complicated is the situation with such a section of mechanics as dynamics. It also examines the movement of bodies and figures for the corresponding quantities. This, for example, speed, distance, time. But there are a number of third-party terms. Here you cannot get away with the simple laws of motion; you will have to consider a mechanical system taking into account the forces acting on a particular body. But statics is already studying the rules of equilibrium in mechanical systems. Not just bodies appear there, but leverage and other elements.
What is the basis of kinematics?
So, we found out that kinematics studies the motion of bodies without regard to the forces that act on material points. But what formed the basis of this section of mechanics, apart from the basic laws? Concepts and definitions are, of course, good, but we cannot use one theory for solving problems. At least in order to achieve a positive or final result, we will have to resort to formulas. And in order to do this, we will first deal with the quantities that will appear in them.
The main quantities used in kinematics problems
To begin with, we want to remind readers that they can be extraordinary. Let's start with a simple quantity that we call distance. This is a scalar quantity. That is, having only a certain value. Three meters on which the ball rolled. 25 meters that the athlete swam. Ten kilometers traveled by a person in a whole day. All of these are numerical values of a quantity that we call distance.
The situation is a little different with speed and acceleration, which in kinematics (and indeed in general) have a twofold nature. On the one hand, we can give the speed a numerical value. Let it be five, ten, twenty meters per second. But speed also has a direction. It coincides with the direction of movement of the body, it is obvious. The situation is similar with acceleration. However, 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 drive, gaining speed every second. In this case, the speed and acceleration are directed in one direction, due to which the speed of the body increases every second. But when braking occurs, the vectors become directed in different directions.
Kinematics is a branch 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 that are most often used to give solutions. Let us consider a fairly simple problem on this topic to finally consolidate in practice the theory obtained earlier in the course of the article.
Task
To verify the characteristics of the car, a hundred-meter segment of the ideal road is allocated. It is known that its acceleration is five meters per second squared. Find out how long the car can travel the specified distance, taking into account the fact that the movement begins from a state of rest.
So, since kinematics is a branch 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 we will carry out a species change for our task. It is said that movement begins from a state of rest. Hence, the initial velocity is zero. Therefore, the product of speed and time V o T will be equal to zero. Since the car accelerates, the “+” sign is characteristic of the formula. As a result, it will take the following form: S = (at ^ 2) / 2.
The next thing is to express the square of time. To do this, we multiply both sides of the resulting equation by two to rewrite it on the line. Now divide the doubled distance by acceleration. The last step for the expression will be to extract the square root of the 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 in a time equal to about 6.32 seconds.