What is mechanical motion and how is it characterized? What parameters are introduced to understand this type of movement? What are the most commonly used terms? In this article we will answer these questions, consider the mechanical motion from different points of view, give examples and solve problems from the physics of the relevant subject.
Even from the school bench, we are taught that a mechanical movement is a change in the position of the body at any time relative to other bodies of the system. In fact, everything is so. Let's take the ordinary house in which we are, behind the zero coordinate system. Imagine visually that the house will be the origin of coordinates, and from it in any directions will be the axis of abscissas and the axis of ordinates.
In this case, our movement within the house, as well as outside it, will visually demonstrate the mechanical movement of the body in the reference frame. Imagine that the point moves along the coordinate system, changing its coordinate relative to both the abscissa axis and the ordinate axis at each moment of time. Everything will be simple and understandable.
Characteristics of mechanical movement
What kind of movement can this be? We will not go deep into the jungle of physics. Let us consider the simplest cases when the motion of a material point occurs. It is subdivided into rectilinear motion, and also into curvilinear motion. In principle, everything should be clear from the title, but let's just in case, let's talk about it more specifically.
A rectilinear motion of a material point will be a motion that takes the form of a straight line along a trajectory. Well, for example, the car rides directly under the road, which has no turns. Or on a section of a similar road. This is the straightforward movement. In this case, it can be uniform or uniformly accelerated.
The curvilinear motion of a material point will be a motion that is traced along a path that does not have the form of a straight line. Trajectory can be a broken line, as well as a closed line. That is, the circular trajectory, ellipsoidal, and so on.
Mechanical movement of the population
This kind of movement has almost absolutely nothing to do with physics. Although, depending on what point of view, we perceive it. What, in general, is called the mechanical movement of the population? They are called resettlement of individuals, which occurs as a result of migration processes. This can be both external and internal migration. By duration, the mechanical movement of the population is divided into a permanent and a temporary (plus the pendulum and seasonal).
If we consider this process from a physical point of view, we can say only one thing: this movement will be perfect to show the movement of material points in the reference system associated with our planet Earth.
Uniform mechanical motion
As is clear from the title, this is a type of movement in which the velocity of the body has a certain value, which is kept constant in absolute value. In other words, the speed of the body, which moves uniformly, does not change. In real life, we practically can not notice ideal examples of uniform mechanical motion. You can reasonably argue, they say, you can go by car at a speed of 60 kilometers per hour. Yes, of course, the speedometer of a vehicle can show a similar value, but that does not mean that in fact the speed of the car will be exactly sixty kilometers per hour.
What is it about? As we know, first, all measuring instruments have a certain error. Rulers, scales, mechanical and electronic devices - they all have a certain error, inaccuracy. You can verify this yourself, taking a dozen rulers and attaching them one to the other. After that, you will notice some discrepancies between the millimeter marks and their application.
The same goes for the speedometer. It has a certain error. At devices the inaccuracy is numerically equal to half of the price of division. In cars, the inaccuracy of the speedometer will be 10 kilometers per hour. That is why at some point we can not say for sure that we are moving with this or that speed. The second factor that will make inaccuracy, will be the forces acting on the car. But the forces are inextricably linked with acceleration, so we'll talk about this a little later.
Very often, uniform motion occurs in problems of a mathematical nature, rather than physical. There motorcyclists, trucks and cars are moving at the same speed, equal in modulus at different times.
Equally accelerated motion
How can we know that the motion is uniformly accelerated? Usually in the tasks information about this is provided directly. That is, there is either a numerical indication of the acceleration, or parameters are given (time, speed change, distance), which allow us to determine the acceleration. It should be noted that acceleration is a vector quantity. So it can be not only positive, but also negative. In the first case we will observe the acceleration of the body, in the second - its braking.
But it happens that information on the type of movement the student is taught in a somewhat secretive, if one can call it that, form. For example, it is said that nothing acts on the body or the sum of all forces is zero. Well, in this case it is necessary to clearly understand that it is a question of uniform motion or rest of the body in a certain coordinate system. If you remember Newton's second law (which says that the sum of all the forces is nothing more than the product of the mass of the body for the acceleration reported under the action of the corresponding forces), then one can easily notice an interesting thing: if the sum of the forces is zero, then the product of the mass by the acceleration will also be zero.
But the mass is we have a constant, and it is not a priori to be zero. In this case, it would be logical to conclude that in the absence of external forces (or compensated) acceleration of the body is missing. So, it is either at rest or moving with constant speed.
The formula of uniformly accelerated motion
Sometimes there is an approach in the scientific literature, according to which light formulas are given first, and then, taking into account some factors, they become more complicated. We will do the opposite, namely, we first consider the uniformly accelerated motion. The formula according to which the distance traveled is calculated as follows: S = V0t + at ^ 2/2. Here V0 is the initial velocity of the body, a is the acceleration (it can be negative, then the + sign will change in the formula to -), and t is the time elapsed from the beginning of the motion to the stop of the body.
Equation of uniform motion
If we talk about uniform motion, we recall that the acceleration is zero (a = 0). Substitute zero in the formula and get: S = V0t. But in fact speed on all part of the road is constant, if we speak roughly, that is, we will have to neglect the forces acting on the body. Which, by the way, is universally practiced in kinematics, since the kinematics does not study the causes of the motion, dynamics is engaged in this. So, if the speed on the whole part of the path is constant, then its initial value coincides with any intermediate, as well as finite. Therefore, the distance formula will look like this: S = Vt. That's all.