First lesson in8 classroomin physics UMK Gromov S.V.

« Mechanics - the science of the movement of bodies »

Lesson Objectives: To introduce students to the section of physics "Mechanics", to give the concept of mechanical motion, the relativity of mechanical motion.

Demonstrations

The ball rolls down the chute

Relative motion of bodies

During the classes

Organizing time. Safety briefing in the classroom in the physics classroom and during laboratory work. Rules of conduct and work in the physics classroom.

Tell about the main content of the physics course in grade 8, recall the design requirements written works, criteria for evaluating the student's response.

Repetition in the form of a short frontal survey:

What does physics study?

What patterns did you notice? Why do you think this is a pattern? How can they be taken into account?

What is science? What methods of scientific knowledge do you know? What has science brought to people's lives?

Introduction to the topic of the lesson

All bodies occupy some space, and all natural phenomena (living and inanimate) proceed in time. Time and space are forms of the existence of matter. common property of all bodies is their movement in space - a change in the position of a body in space relative to other bodies over time -mechanical movement . Therefore, the concept of movement is meaningless without specifyingreference systems orreference body , i.e.relatively what other body is moving.

Mechanics is a branch of physics that studies the movement of bodies and the concepts of force and energy associated with it.

The main task of mechanics - determination of the position of a body in space relative to other bodies at any time.

Kinematics - This is a branch of mechanics that describes the movement of bodies without taking into account the reasons that cause it.

Dynamics is a branch of mechanics that explains the causes of the motion of bodies.

Statics is a branch of mechanics that studies the conditions for the equilibrium of bodies.

Basic concepts of mechanics

1. Mechanical movement

2. Material point

3. Reference system

4. Trajectory

5. Path

6. Move

7. Relativity

Ways to describe movements

1. Tabular

2. Graphic

3. Analytical

Uniform movement. The concept of average speed (average time, average path)

Consolidation of what has been learned.

Is it possible to consider this ball as a material point when determining the volume of a steel ball using a beaker?

Is it possible to take a car for material point, if at the same time the problem “Will the car pass through the gate of the fence?”

Which parts of the bike move almost forward and which do not? Does the type of movement of bicycle parts depend on the choice of reference system?

What is the trajectory of the pen tip?

Interactive crossword to consolidate the material

Zeno's paradox: “A flying arrow does not fly, since it is at rest at each point of the trajectory (there can be no movement at a point). At any moment of time it is at rest, and, therefore, it does not move at all. Let's try to unravel the tangle of Zeno's paradox.

Summing up the lesson.

Setting homework.

Sources:

Gromov S.V. "Physics Grade 8", Enlightenment

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The science of the movement of bodies

First letter "m"

Second letter "e"

Third letter "x"

The last beech is the letter "a"

Answer for the clue "The science of the movement of bodies", 8 letters:
Mechanics

Alternative questions in crossword puzzles for the word mechanic

branch of technology

Favorite science of Vintik and Shpuntik

Moving parts of the machine (gen.)

"Skin-wool" branch of physics

The science that studies the movement of bodies

Word definitions for mechanic in dictionaries

Dictionary Russian language. D.N. Ushakov The meaning of the word in the dictionary Explanatory dictionary of the Russian language. D.N. Ushakov
mechanics, pl. no, w. (Greek mechanike). department of physics - the doctrine of motion and forces. Theoretical and applied mechanics. Hidden, complex device, background, essence of something. (colloquial). Tricky mechanics. He, as his respected fellow citizens say, happened ...

Explanatory Dictionary of the Living Great Russian Language, Vladimir Dal The meaning of the word in the dictionary Explanatory Dictionary of the Living Great Russian Language, Vladimir Dal
and. mathematics applied to the laws of equilibrium and motion of bodies; the science of force and resistance to it; the art of applying force to a cause and building machines; the science of the favorable adaptation of forces. -nic, -nic, relating to mechanics; physical, based on...

New explanatory and derivational dictionary of the Russian language, T. F. Efremova. The meaning of the word in the dictionary New explanatory and derivational dictionary of the Russian language, T. F. Efremova.
and. scientific discipline studying the simplest form the motions of matter and the interactions between them connected with the motion of bodies. Academic subject containing theoretical basis of this discipline. unfold A textbook that sets out the content of this academic subject ....

Wikipedia The meaning of the word in the Wikipedia dictionary
Mechanics - a branch of physics, a science that studies movement material bodies and interaction between them; at the same time, movement in mechanics is a change in time of the relative position of bodies or their parts in space.

Examples of the use of the word mechanics in the literature.

High-speed electronic calculating machines make it possible to solve a wide variety of problems with tremendous speed and great accuracy, for example, in the field of intra-atomic processes, jet technology, radar, aircraft engineering, construction mechanics and other industries.

Gradually mechanic and the alien began to talk, they began to understand each other on the basis of motorists.

In those same years, I remember, a very representative joint meeting of the Ministry of Instrument Engineering, Automation and Control Systems and the Department of mechanics and management processes of the Academy of Sciences of the USSR.

The mathematician Adadurov became well received, mechanic Ladyzhensky, architect Ivan Blank, assessors from various collegiums, doctors and gardeners, army and navy officers came to the light.

Miracle mechanics- magician and acrobat, - Del whispered in his ear, as if announcing the number of the performance.

This is the science of the movement of bodies.

According to the nature of the tasks to be solved, mechanics is divided into two main parts: kinematics and dynamics.

AT kinematics(from Greek word"kinema" - movement) describes how bodies move, without explaining the reasons why they move that way.

The causes that cause this or that movement are studied in dynamics(from the Greek word "dynamis" - strength).

Recall that mechanical movement body is the process of changing its position relative to some other body chosen as the reference body. Therefore, in order to to judge whether a given body is moving or not, you must first select a reference body, and then see if the position of the body under consideration changes relative to the selected reference body. In this case, the body can move relative to one reference body and not move relative to another reference body.

For example, a stone lying on the ground is at rest relative to the Earth, but moves (together with the Earth) relative to the Sun.

To determine the position of the body in space, scientists use coordinate system- three mutually perpendicular axes X, Y, Z. Time is measured using a clock. The totality of the body of reference, the coordinate system associated with it and the clock is called reference system.

mechanical movement relatively. It means that:

1) it is meaningless to talk about the motion of a body without specifying the reference body with respect to which this motion is considered;
2) with respect to different reference bodies (for example, the Earth, the Sun, an airplane, etc.), the same movement may look different: the trajectories of movement, the distance traveled, speeds, etc. may be different.

But along with relativity, mechanical motion also has features of absoluteness. Absolute are called such properties of motion that do not depend on the choice of the body of reference. For example, if relative to the Earth two bodies A and B approach each other, then their approach will also occur relative to any other reference body (car, moon, sun, etc.). In other words, it is impossible to find such a reference body, in relation to which these two bodies A and B would not approach, but, for example, would move away from each other. The convergence of these bodies is absolute.

The problems associated with the movement of bodies have interested people since time immemorial. Research into these problems was motivated both by the practical needs of people and by the curiosity of the researchers themselves. Solving mechanical problems often required a lot of intelligence (think of Archimedes, for example). Therefore, it is not surprising that the very name of the science of movement bodies (mechanics) is translated as "cunning, trick".
Thinking about the movement of bodies, ancient Greek scientists sometimes came up with unusual paradoxes. The most surprising among them are the paradoxes of Zeno of Elea (5th century BC). The paradoxes invented by him (or, as they are also called, aporias) continue to be discussed by scientists for two and a half thousand years!

The most famous, perhaps, is the aporia of Zeno called "Achilles and the tortoise". In it, Zeno proves that the hero of the Trojan War, Achilles, despite his fast legs, will not be able to catch up even with a slow tortoise. Let, says Zeno, Achilles start running after the tortoise, simultaneously taking a start at a certain distance AB behind it (Fig. 1). It is clear that before Achilles catches up with the tortoise, he must first pass the distance AB separating them. But while he runs this distance, the tortoise will also crawl forward a little, and Achilles will have to overcome the additional distance BC. But while he does this, the tortoise will again go ahead, and Achilles will again have to overcome additional distance. During this time, the turtle will crawl the next segment of the path, and so on, ad infinitum. As a result, in order to catch up with the tortoise, Achilles will need to overcome an infinite number of segments of the path, and, consequently, an infinitely long time. But this means that he will never catch up with her!

In fact, of course, Achilles (like any other person) will easily catch up and overtake the tortoise crawling ahead. But this is the paradox: how does a person manage to catch up with a tortoise in practice, if theoretically (from the point of view of Zeno) this is impossible?

Another aporia of Zeno - "Stadium" - leads to a no less strange conclusion. There are three rows of bodies in the stadium (Fig. 2, a). Row 1 is at rest. Rows 2 and 3 begin to move towards each other at the same speed and after a while they find themselves in the position shown in Figure 2, b. In this case, the first body of row 3 simultaneously passes by the entire row 2, i.e. some distance S, and past half of row 1, i.e. distance s/2. Since both of these distances are traveled simultaneously, it turns out that the whole is equal to its half:
S = s/2


But this is absurd! Given that we have come to this ridiculous conclusion, assuming that rows 2 and 3 are moving, we must therefore admit that in fact they cannot move!

Movement does not exist - Zeno came to such a strange conclusion.

It is curious that when another ancient Greek philosopher, Diogenes, was introduced to the paradoxes of Zeno, he stood up and silently began to pace back and forth, thereby showing in practice that movement still exists!

Many centuries later, wishing to pay tribute to the wit of Diogenes, A. S. Pushkin wrote:

There is no movement, said the bearded sage,

The other was silent and began to walk before him...

However, Diogenes was wise enough to understand that one cannot refute Zeno by walking ... Moreover, when one of his students was satisfied with this "refutation", Diogenes began to beat him with a stick on the grounds that "one should not be satisfied with sensual certainty, but needs to be understood!"

So if you want to find a solution to Zeno's paradoxes, then this must be done not by practice, but by looking for errors in Zeno's own reasoning.
It must be said that there is still no generally accepted solution to Zeno's paradoxes. An analysis of the problems uncovered by Zeno showed that strange and even contradictory properties are indeed inherent in mechanical motion. And one of these properties is the property of relativity.

Zeno was the first to face the problem relativity of motion. In his aporia "Stadium" he considers the motion of a body with respect to two different reference bodies (one reference body is row 1, the other is row 2). The description of motion with respect to two different reference bodies gave different results. But correct conclusion What needs to be done here is not the impossibility of motion, but the existence of an inherent property of relativity.

1. What is mechanics? 2. What is the difference between kinematics and dynamics? 3. What is called mechanical movement? 4. What is meant by the relativity of motion? 5. Who is on the move: a passenger on the bus or a person standing at the bus stop?

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