Straightforward motion

Modern mechanics knows several types of motion. They differ from each other trajectory, the presence or absence of acceleration and a number of other parameters. However, they also have common features: in particular, each kind of kinematic action can be expressed with the aid of a coordinate line. Thus, rectilinear motion has a straight line trajectory, which is clear from its name. Let us consider this case in more detail.

Uniform rectilinear motion is a motion characterized by moving to equal distances at identical intervals of time. Simply put, for every selected period of time (be it 1, 2, 3 seconds or 10 minutes) the body will overcome the distance, absolutely equal to that which will be overcome for the next same time interval. Strictly speaking, the ideal rectilinear motion is rather an abstract model, since it is almost impossible to achieve such a displacement under normal conditions: there are always obstacles. Among them - air resistance, features of the moving body and others.

The formula for such a movement is as simple as possible and has been known since high school:

S = v / t,

Where s is the distance traveled by the body over a certain length of time, v is the velocity during this movement, t is the actual distance travel time. It is logical that the speed with this movement is also constant and unchanged.

Equal rectilinear motion is a special case of the one described above with the only difference that here we have a motion with acceleration. The formula for it looks like this:

S = Vo + - at2 / 2

It is read as: es (distance) is equal to zero (initial speed) plus-minus a (acceleration) te (time) square divided by two. The sign "+ -" is not accidental. The point is that the rectilinear motion with acceleration can be either uniformly accelerated or equally slowed down. The first case corresponds to a formula with a plus, the second - with a minus. Examples: acceleration and braking of the train. In the case when the train has gained the necessary speed and does not need more acceleration, it moves with a relatively stable speed, that is, it makes a rectilinear motion.

It is also worth considering such a kind of movement as the uneven straight line. A body moving in this way has a speed that can change without any system, that is, at an arbitrary moment in time. Therefore, it is customary to distinguish it from the so-called average speed. The uneven PD differs from the uniform one in that the speed can vary throughout the whole path (as a rule, in real life we are dealing with this type of motion). However, it is impossible to measure speed at any particular time, and is not required. For this purpose, such a notion as average speed was introduced . Its formula is exactly the same as the speed formula for a uniform PD:

V = s / t,

With the only difference is that it is impossible to find a specific position at any given time, but it is possible to determine what distance has been traveled within a given time.

Unlike the average, the instantaneous velocity with nonuniform PD is the speed that the body has at a particular moment in time.

Now, when the specificity of the movement with equal speed is more or less uncovered, it is important to clarify and distinguish between rectilinear and curvilinear motion. Considering the fact that linear motion in mechanics almost always means straightforward, it is worth noting: scientists believe that such a motion is a particular case of curvilinear motion. The definition of the curvilinear motion is: a motion whose trajectory corresponds not to a straight line, but to a curve of a line. Probably, because the ideal straight line does not exist (only as an abstraction), and what we have accepted as a direct trajectory is only an approximate value of that, we can really consider a rectilinear motion as a curvilinear one.