Examples of mechanical motion. Mechanical Movement: Physics, Grade 10

Examples of mechanical motion are known to us from everyday life. These are cars passing by, flying planes, floating ships. The simplest examples of mechanical motion we create ourselves, passing by other people. Every second our planet moves in two planes: around the Sun and its axis. And these are also examples of mechanical motion. So let's talk about this more specifically today.

What is the mechanics

Before we say what examples of mechanical motion exist, let's look at what is called mechanics. We will not go into the scientific jungle and operate with a huge number of terms. Speaking absolutely simply, mechanics is a branch of physics that studies the motion of bodies. And what could it be, this mechanic? Students at physics classes get acquainted with its subsections. This is kinematics, dynamics and statics.

Each of the subsections also studies the motion of bodies, but it has characteristics unique to it. Which, by the way, is widely used in solving relevant problems. Let's start with kinematics. Any modern school textbook or electronic resource will make it clear that the movement of the mechanical system in kinematics is considered without taking into account the causes leading to movement. At the same time, we know that the reason for the acceleration that will cause the body to move is force.

What if forces need to be taken into account

But the consideration of the interaction of bodies in motion is the next section, which is called dynamics. Mechanical movement, the speed in which is one of the important parameters, is inextricably linked to this concept in dynamics. The last section is statics. She studies the equilibrium conditions of mechanical systems. The simplest static example is the balancing of the hour of weights. Note to teachers: a lesson on physics "Mechanical Movement" in school should start with this. First, give examples, then divide the mechanics into three parts, and only then proceed to the rest.

What are the tasks

Even if we turn to just one section, suppose it's kinematics, there's a lot of different tasks waiting for us. The whole point is that there are several conditions on the basis of which, the same task can be presented in a different light. Moreover, the problems of the kinematic motion can be reduced to cases of free fall. We will now talk about this.

What is a free fall in kinematics?

This process can be given several definitions. However, they will inevitably be reduced to one point. With a free fall, only gravity acts on the body. It is directed from the center of mass of the body along the radius to the center of the Earth. In the rest, you can "twist" the wording and definition as soon as you like. However, the presence of gravity alone in the process of such motion is a prerequisite.

How to solve the problem of free fall in kinematics

To begin with, we need to "get hold of" formulas. If you ask a modern teacher in physics, he will tell you that knowing the formulas is already half the solution of the problem. A quarter is devoted to an understanding of the process and another quarter to the computation process. But formulas, formulas and once again formulas - that's what makes up the help.

We can call the free fall a particular case of uniformly accelerated motion. Why? Yes, because we have everything that is needed for this. Acceleration does not change, it is 9.8 meters per second in the square. On this basis, we can move on. The formula for the distance traveled by the body with uniformly accelerated motion has the form: S = Vot + (-) at ^ 2/2. Here S is the distance, Vo is the initial velocity, t is the time, and a is the acceleration. Now let's try to bring this formula to the case of free fall.

As we said earlier, this is a special case of uniformly accelerated motion. And if a is a conventional conventional acceleration designation, then g in the formula (replace a) will have a definite numerical value, also called tabular. Let's rewrite the formula of the distance traveled by the body for the case with a free fall: S = Vot + (-) gt ^ 2/2.

It is clear that in this case the motion will occur in the vertical plane. We draw the readers' attention to the fact that none of the parameters that we can express from the above formula is independent of the body weight. Will you throw a box or a stone, for example, from a roof, or two different masses of stone - these objects with the simultaneous beginning of the fall and land almost simultaneously.

Free fall. Mechanical motion. Tasks

By the way, there is such a thing as instantaneous speed. It denotes the velocity at any instant of time. And with a free fall, we can easily determine it, knowing only the initial speed. And if it is equal to zero, then the matter at all trifling. The formula for instantaneous velocity with free fall in kinematics is: V = Vo + gt. Notice that the "-" sign is missing. After all, it is put when the body slows down. And how can a body slow down when it falls? Thus, if the initial velocity has not been reported, the instantaneous velocity will be equal simply to the product of the acceleration of gravity g by the time t that has elapsed since the moment of the beginning of the motion.

Physics. Mechanical motion with free fall

Let's move on to specific tasks on this topic. Suppose the following condition. The children decided to have fun and drop the tennis ball from the roof of the house. Find out what the speed of a tennis ball was when it hit the ground, if the house has twelve floors. The height of one floor is equal to three meters. The ball is released from the hands.

The solution to this problem will not be one-step, as one might think first. It seems that everything seems simple, only to substitute the necessary numbers in the formula of instantaneous speed and that's all. But when we try to do this, we can face a problem: we do not know the time of the ball's fall. Let's look at the rest of the task.

Tricks in the conditions

Firstly, we are given the number of floors, and we know the height of each of them. It is three meters. Thus, we can immediately calculate the normal distance from the roof to the ground. Secondly, we are told that the ball is released from the hands. As usual, in problems of mechanical motion (and in problems in general) there are small details that at first glance may seem useless. However, here this expression indicates that the tennis ball has no initial speed. Well, one of the terms in the formula then disappears. Now we need to know the time that the ball was in the air before collision with the ground.

For this we need a distance formula for mechanical motion. First of all, we remove the product of the initial velocity by the time of motion, since it equals zero, and hence the product will be zero. Then multiply both sides of the equation by two to get rid of the fraction. Now we can express the square of time. For this, the divided distance is divided by the acceleration of gravity. We can only extract the square root of this expression to find out how much time has passed before the ball hits the ground. Substitute the numbers, extract the root and get approximately 2.71 seconds. Now we substitute this number into the instantaneous velocity formula. Get about 26.5 meters per second.

Note to teachers and students: you could go a little different way. In order not to be confused in these numbers, it is necessary to simplify as much as possible the final formula. This will be useful in that there will be less risk of getting confused in your own calculations and making an error in them. In this case, we could proceed as follows: express time from the distance formula, but not substitute the numbers, and substitute this expression in the instantaneous velocity formula. Then it would look like this: V = g * sqrt (2S / g). But after all, the acceleration of free fall can be introduced into the radicand. To do this, we will represent it in a square. We obtain V = sqrt (2S * g ^ 2 / g). Now we reduce the acceleration of free fall in the denominator, and in the numerator we erase its degree. As a result, we obtain V = sqrt (2gS). The answer will be the same, only the calculation will be less.

Results and conclusion

So, what did we learn today? There are several sections that physics studies. The mechanical movement in it is subdivided into static, dynamic, and kinematics. Each of these mini-sciences has its own characteristics, which are taken into account when solving problems. However, we can give a general description of such a concept as mechanical motion. 10 class - the time of the most active study of this section of physics, if you believe the school program. Mechanics includes cases of free fall, because they are particular types of uniformly accelerated motion. And with these situations, we work with kinematics.