space research. Semiconductor diode, p-p - transition and its properties. The use of semiconductor devices. The task is to apply the 1st law of thermodynamics.

body momentum- this is the product of the body's mass and its speed p \u003d mv (kg * m / s) The momentum of the body is the amount of motion. The change in the momentum of the body is equal to the change in the momentum of the force. ∆p = F∆t
The sum of impulses of bodies before interaction is equal to the sum of impulses after interaction OR: The geometric sum of impulses of bodies in a closed system remains constant. m1v1 + m2v2 = const

The law of conservation of momentum underlies jet propulsion - this is a movement in which part of the body is separated, and the other receives additional acceleration.
Jet propulsion in technology: FOR EXAMPLE (in airplanes and rockets)
Jet propulsion in nature: FOR EXAMPLE (clams, octopuses). Space information is of great importance for the further development of science and technology. Space research, apparently, will lead in the near future to revolutionary changes in many areas of engineering and technology, as well as in medicine. The results of developments in the field of space technology will find application in industrial and agricultural work, in the study of the depths of the World Ocean and in polar research, in sports competitions, in the manufacture of geological equipment and in other areas. A semiconductor diode is a semiconductor device with one electrical junction and two leads (electrodes). An electron-hole junction is a region of a semiconductor in which a spatial change in the type of conductivity takes place (from an electronic n-region to a hole p-region). Semiconductor devices are used: in the motor transport complex. electronic ignition. electronic control unit. LEDs: sensors, headlights, traffic lights, etc. global positioning system. Cell Phones

6 Law of gravity. Gravity. Free fall of bodies. Body weight. Weightlessness. A magnetic field. Magnetic induction, lines of magnetic induction. Ampere force and its application. The task is to apply the formulas for work or direct current power.

Law of gravity Newton - a law describing the gravitational interaction in the framework of classical mechanics. This law was discovered by Newton around 1666. It states that the force of gravitational attraction between two material points of mass and, separated by a distance, is proportional to both masses and inversely proportional to the square of the distance between them. Gravity- the force acting on any material body located near the surface of the Earth or another astronomical body. Free fall- uniformly alternating motion under the action of gravity, when other forces acting on the body are absent or negligible. Weight- the force of the body on the support (or suspension or other type of fastening), preventing the fall, arising in the field of gravity P=mg. Weightlessness- a state in which the force of interaction of the body with the support (body weight), arising in connection with gravitational attraction, the action of other mass forces, in particular the force of inertia arising from the accelerated movement of the body, is absent. A magnetic field- a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their movement. Magnetic induction- vector quantity, which is a force characteristic of the magnetic field (its action on charged particles) at a given point in space. Determines the force with which the magnetic field acts on a charge moving at speed.
Lines of magnetic induction- lines, tangents to which are directed in the same way as the vector of magnetic induction at a given point of the field.

7 The phenomenon of electromagnetic induction, the use of this phenomenon. The law of electromagnetic induction. Lenz's rule. Job. Fur. energy. Kinetic and potential energy. The law of conservation of fur. energy. E.Z: Measurement of the total resistance of an electrical circuit in a series connection. Electromagnetic induction is the phenomenon of the appearance of an electric torus in a closed circuit when the magnetic flux passing through it changes. It was discovered by Michael Faradel. The phenomenon of email Poppy. induction used in electrical and radio engineering devices: generators, transformers, chokes, etc. Faraday's law of electromagnetic induction is the basic law of electrodynamics concerning the principles of operation of transformers, chokes, many types of electric motors and generators. The law says: for any closed circuit, the induced electromotive force (EMF) is equal to the rate of change of the magnetic flux passing through this circuit, taken with a minus sign. Lenz's rule defines the direction of the induction current and says: the induction current always has such a direction that it weakens the effect of the cause that excites the current. Fur. Work- this is a physical quantity, which is a scalar quantitative measure of the action of a force or forces on a body or system, depending on the numerical value, the direction of the force (forces) and on the displacement of a point (points), body or system In physics fur. energy describes the sum of potential and kinetic energies present in the components of a mechanical system. Fur. energy- this is the energy associated with the movement of an object or its position, the ability to perform mechanical work. The law of conservation of fur. energy states that if a body or system is subjected to the action of only conservative forces (both external and internal), then the total mechanical energy of this body or system remains constant. In an isolated system where only conservative forces act, the total mechanical energy is conserved. Potential is the potential of the body, it personifies what kind of work the body CAN do! And the kinetic force is the force that is already doing the work. Law of energy conservation- the law of nature, established empirically and consisting in the fact that for an isolated physical system, a scalar physical quantity can be introduced, which is a function of the parameters of the system and is called energy, which is conserved over time. Since the law of conservation of energy does not refer to specific quantities and phenomena, but reflects a general pattern that is applicable everywhere and always, it can be called not a law, but the principle of conservation of energy. Potential energy- energy which is determined by the mutual position of interacting bodies or parts of the same body. Kinetic energy- the case when the body moves under the influence of a force, it not only can, but also does some work

8 Mechanical vibrations, characteristics mech. oscillations: amplitude, period, frequency. Free and forced vibrations. Resonance. Self-induction. Inductance. The energy of the magnetic field of the coil. The task of applying the law of conservation of momentum A mechanical oscillation is called an exactly or approximately repetitive motion, in which the body is displaced first in one direction, then in the other direction from the equilibrium position. If the system is capable of performing oscillatory motions, then it is called oscillatory. Properties of the oscillatory system: The system has a position of stable equilibrium. When the system is taken out of equilibrium, an internal restoring force arises in it. The system has inertia. Therefore, it does not stop at the equilibrium position, but passes it. Oscillations that occur in the system under the action of internal forces are called free vibrations.. All free oscillations are damped. (For example: string vibration after being struck) Oscillations made by bodies under the action of external periodically changing forces are called forced (for example: vibration of a metal workpiece when a blacksmith works with a hammer). Resonance- a phenomenon in which the amplitude of forced oscillations has a maximum at a certain value of the frequency of the driving force. Often this value is close to the frequency of natural vibrations, in fact, it may coincide, but this is not always the case and is not the cause of resonance. self induction- this is the phenomenon of the occurrence of an EMF of induction in a conducting circuit when the current flowing through the circuit changes. When the current in the circuit changes, the magnetic flux through the surface bounded by this circuit also changes proportionally. A change in this magnetic flux, due to the law of electromagnetic induction, leads to the excitation of an inductive EMF (self-induction) in this circuit. Inductance- coefficient of proportionality between the electric current flowing in any closed circuit, and the magnetic flux created by this current through the surface, the edge of which is this circuit. There is a magnetic field around the conductor with current, which has energy.

9 Mech. waves. Wavelength, wave propagation speed and the relationship between them. thermonuclear reaction. The use of atomic energy. Prospects and problems of development of nuclear power. E.Z: determination of the refractive index of a glass plate. Fur. waves are perturbations propagating in an elastic medium (deviations of the particles of the medium from the equilibrium position). If particle oscillations and wave propagation occur in the same direction, the wave is called longitudinal, and if these movements occur in perpendicular directions, it is called transverse. Longitudinal waves accompanied by tensile and compressive strains can propagate in any elastic media: gases, liquids and solids. Transverse waves propagate in those media where elastic forces appear during shear deformation, i.e., in solids. When a wave propagates, energy is transferred without transfer of matter. The speed at which a disturbance propagates in an elastic medium is called the wave speed. It is determined by the elastic properties of the medium. The distance over which a wave propagates in a time equal to the period of oscillation in it is called the wavelength (lambda). Wavelength- the distance that the wave has time to overcome moving in space at the speed of light in one period, which in turn is the reciprocal of the frequency. The higher the frequency, the shorter the wavelength. thermonuclear reaction- a kind of nuclear reaction in which light atomic nuclei are combined into heavier ones due to the kinetic energy of their thermal motion. The development of an industrial society relies on an ever-increasing level of production and consumption of various types of energy. (Sharply reduces the use of natural resources

10 The emergence of the atomistic hypothesis of the structure of matter and its experimental evidence: diffusion, Brownian motion. Basic provisions of the ICT. Mass, sizes of molecules. Electromotive force. Ohm's law for a complete circuit. The task of applying the fur formula. work

Diffusion is the phenomenon of the spread of particles of one substance between the particles of another

Brownian motion- this is the movement of particles insoluble in a liquid under the action of liquid molecules Molecular-kinetic theory is the study of the structure and properties of matter based on the idea of ​​the existence of atoms and molecules as the smallest particles of chemical substances At the heart of molecular kinetic theory There are three main provisions: .All substances - liquid, solid and gaseous - are formed from the smallest particles - molecules, which themselves consist of atoms. .Atoms and molecules are in continuous chaotic motion. Particles interact with each other by forces that are electrical in nature. The gravitational interaction between particles is negligible. m 0 is the mass of the molecule (kg). The molecular size is very small. Electromotive force forces, that is, any forces of non-electrical origin, operating in quasi-stationary circuits of direct or alternating current.

Ohm's law for a complete circuit- the current strength in the circuit is proportional to the EMF acting in the circuit and inversely proportional to the sum of the circuit resistances and the internal resistance of the source.

11 Electromagnetic waves to and from properties. The principle of radio communication. The invention of radio, modern means of communication. Temperature and its measurement Absolute temperature. Temperature is a measure of the average kinetic energy of the movement of molecules. E.Z: Measurement of the optical power of a converging lens.

Electromotive force- scalar physical quantity characterizing the work of third-party forces, that is, any forces of non-electrical origin, operating in quasi-stationary circuits of direct or alternating current. The device of general schemes for organizing radio communication. A characteristic of a radio information transmission system in which telecommunication signals are transmitted by means of radio waves in open space. Radio- a type of wireless information transmission, in which radio waves freely propagating in space are used as an information carrier. On May 7, 1895, Russian physicist Alexander Stepanovich Popov (1859 - 1905/06) demonstrated the world's first radio receiver. Modern means of communication This is a telephone, walkie-talkie, etc. Temperature- physical quantity characterizing the thermal state of bodies. Temperature is measured in degrees.

Absolute temperature is an unconditional measure of temperature and one of the main characteristics

thermodynamics. Temperature is a measure of the average kinetic energy of molecules, the energy

proportional to temperature.

12 Work in thermodynamics. Internal energy. First and second laws of thermodynamics. Alternator. Transformer. Production and transmission of electricity, energy saving at home and at work. E.Z: Measurement of free fall acceleration at a given point on the earth.

In thermodynamics the movement of the body as a whole is not considered, we are talking about the movement of parts of a macroscopic body relative to each other. As a result, the volume of the body can change, and its speed remains equal to zero. . Work in thermodynamics is defined in the same way as in mechanics, but it is not equal to

a change in the kinetic energy of the body, but a change in its internal energy. Internal energy body (denoted as E or U) - the total energy of this body minus the kinetic energy of the body as a whole and the potential energy of the body in an external field of forces. Consequently, the internal energy is made up of the kinetic energy of the chaotic motion of molecules, the potential energy of interaction between them, and the intramolecular energy. First law of thermodynamics The change ΔU of the internal energy of a non-isolated thermodynamic system is equal to the difference between the amount of heat Q transferred to the system and the work A performed by the system on external bodies.

Second law of thermodynamics. It is impossible to transfer heat from a colder system to a hotter one in the absence of other simultaneous changes in both systems or surrounding bodies. alternator is a device that produces alternating current

A transformer is a device used to increase or decrease current or voltage. Energy saving - the creation of new technologies that consume less energy (new lamps, etc.)

Thermal engines. efficiency of heat engines. Thermal engines and ecology. Radar, the use of radar. Experimental task: measuring the length of a light wave using a diffraction grating.

heat engine- a device that performs work through the use of internal energy, a heat engine that converts heat into mechanical energy, uses the dependence of the thermal expansion of a substance on temperature.

Coefficient of performance (COP) of a heat engine is the ratio of the work A´ done by the engine to the amount of heat received from the heater:

The continuous development of energy, automobile and other types of transport, the increase in the consumption of coal, oil and gas in industry and for domestic needs increases the possibility of meeting the vital needs of a person. However, at present, the amount of chemical fuel burned annually in various thermal engines is so large that the protection of nature from the harmful effects of combustion products is becoming an increasingly difficult problem. The negative impact of thermal machines on the environment is due to the action of various factors.

Radar- a field of science and technology that combines methods and means of location (detection and measurement of coordinates) and determination of the properties of various objects using radio waves.

Radar-guided missiles are equipped with special autonomous devices to perform combat missions. Ocean-going ships use radar systems for navigation. On aircraft, radars are used to solve a number of problems, including determining the flight altitude relative to the ground.

Law of conservation of momentum

In subsection (5.8), the concept of momentum of an arbitrary body was introduced and equation (5.19) was obtained, which describes the change in momentum under the action of external forces. Since the change in momentum is due only to outside forces, then equation (5.19) is convenient to apply to describe the interactions of several bodies. In this case, interacting bodies are considered as one complex body (system of bodies). It can be shown that complex body momentum (system of bodies) is equal to the vector sum of the impulses of its parts:

p \u003d p 1 + p 2 + ... (9.13)

For a system of bodies, an equation of the form (5.13) is written without any changes:

dp = F dt.(9.14)

Change of momentum system of bodies is equal to the impulse of external forces acting on it.

Consider some examples illustrating the operation of this law.

On fig. 9.10, and the athlete is standing, leaning with her right foot on the skateboard, and with her left foot she is pushing off the ground. The speed achieved during the push depends on the force of the push and on the time during which this force acts.

On fig. 9.10, b depicts a javelin thrower. The speed that a javelin of a given mass will acquire depends on the force applied by the athlete's hand and on the time during which it is applied.

Rice. 9.10. a) An athlete on a skateboard; b) javelin thrower

Rice. 9.11.

Shot put

Therefore, before throwing the javelin, the athlete brings his hand far back. A similar process is analyzed in more detail in the example of an athlete pushing the shot, fig. 9.11.

Equation (9.14) implies one consequence important for practical application, called the law of conservation of momentum. Consider a system of bodies that is not acted upon by external forces. Such a system is called closed.

A system of bodies that interact only with each other and do not interact with other bodies is called closed.

There are no external forces for such a system. (F= 0 and dp= 0). Therefore, there is law of conservation of momentum.

The vector sum of the impulses of the bodies, included in a closed system, remains unchanged (preserved).

In other words, for any two moments of time, the momenta of a closed system are the same:

p1=p2(9.15)

The law of conservation of momentum is a fundamental law of nature that knows no exceptions. It is absolutely strictly observed both in the macrocosm and in the microcosm.

Of course, a closed system is an abstraction, since in almost all cases there are external forces. However, for some types of interactions with a very short duration, the presence of external forces can be neglected, since with a small interval of action, the force impulse can be considered equal to zero:

F dt 0→dp 0.

Short duration processes are

Collisions of moving bodies

Disintegration of the body into parts (explosion, shot, throw).

Examples

In action films, there are often scenes in which, after being hit by a bullet, a person is thrown away in the course of the shot. On the screen, it looks pretty impressive. Let's see if this is possible? Let the mass of people M\u003d 70 kg and at the moment the bullet hits it is at rest. We take the mass of the bullet equal to t = 9 g and her speed v= 750 m/s. If we assume that after hitting a bullet, a person starts moving (in fact, this can be prevented by the friction force between the soles and the floor), then for the man-bullet system, we can write the law of conservation of momentum: p 1 = r 2. Before the bullet hits the person does not move and in accordance with (9.9) the momentum of the system p 1 \u003d m∙v+0. We will assume that the bullet gets stuck in the body. Then the final momentum of the system R 2 = (M + m)∙u, where and- the speed that a person received when a bullet hit. Substituting these expressions into the momentum conservation law, we obtain:

The result obtained shows that there can be no question of any flying off of a person by several meters (by the way, a body thrown upwards at a speed of 0.1 m / s will rise to a height of only 0.5 mm!).

2) Clash of hockey players.

Two hockey players M 1 and M 2 move towards each other with speeds, respectively, v1, v2(Fig. 9.12). Determine the total speed of their movement, counting the collision absolutely inelastic(with an absolutely inelastic impact, the bodies "cling" and move further as a whole).

Rice. 9.12. Absolutely inelastic collision of hockey players

We apply the law of conservation of momentum to a system consisting of two hockey players. Momentum of the system before the collision p 1 \u003d M 1 ∙v 1- M 2 v 2. There is a “-” sign in this formula because the speeds v1 and v2 directed towards each other. Speed ​​direction v1 considered positive, and the direction of velocity v2- negative. After an inelastic collision, the bodies move with a common velocity v and momentum of the system p 2 \u003d (M l + M 2) ∙ v. We write down the law of conservation of momentum and find the speed v:

Speed ​​direction v determined by its sign.

Let us pay attention to one important circumstance: the law of conservation of momentum can only be applied to free bodies. If the motion of one of the bodies is limited by external constraints, then the total momentum will not be conserved.

Jet propulsion

Jet propulsion is based on the use of the law of conservation of momentum. This is the name of the movement of the body that occurs when a part of it separates from the body at some speed. Consider rocket propulsion. Let the rocket and its mass along with the fuel M rests. The initial momentum of the rocket with fuel is zero. During the combustion of a portion of the fuel mass T gases are formed, which are ejected through the nozzle with a speed u. According to the law of conservation of momentum, the total momentum of the rocket and fuel saved: p 2 = p 1→ m∙u +(M - m)∙v = 0, where v- the speed obtained by the rocket. From this equation we find: v = ─t∙u /(M ─ t). We see that the rocket acquires a speed directed in the direction opposite to the direction of the gas ejection. As the fuel burns, the speed of the rocket continuously increases.

An example of jet propulsion is the recoil when fired from a rifle. Let the rifle, the mass of which m 1 = 4.5 kg, shoots a bullet with a mass t 2 = 11g flying at speed v 1 = 800 m/s. From the law of conservation of momentum, the recoil velocity can be calculated:

Such a significant recoil rate will occur if the rifle is not pressed to the shoulder. In this case, the shooter will receive a strong blow with the butt. With the correct shooting technique, the shooter presses the rifle to the shoulder and the recoil is perceived by the entire body of the shooter. With an arrow mass of 70 kg, the recoil velocity in this case will be equal to 11.8 cm / s, which is quite acceptable.

MINISTRY OF GENERAL AND PROCESSIONAL EDUCATION OF THE ROSTOV REGION

STATE EDUCATIONAL INSTITUTION SREDNENGO

OF VOCATIONAL EDUCATION IN THE ROSTOV REGION

"SALSK INDUSTRIAL COLLEGE"

METHODOLOGICAL DEVELOPMENT

training session

in the discipline "Physics"

Topic: "Pulse. Law of conservation of momentum. Jet propulsion".

Developed by teacher: Titarenko S.A.

Salsk

2014

Topic: “Impulse. Law of conservation of momentum. Jet propulsion".

Duration: 90 minutes.

Lesson type: Combined lesson.

Lesson Objectives:

educational:

reveal the role of conservation laws in mechanics;

give the concept of "momentum of the body", "closed system", "reactive motion";

teach students to characterize physical quantities (body momentum, force impulse), apply a logical scheme when deriving the law of conservation of momentum, formulate the law, write it in the form of an equation, explain the principle of jet propulsion;

apply the law of conservation of momentum when solving problems;

promote the assimilation of knowledge about the methods of scientific knowledge of nature, the modern physical picture of the world, the dynamic laws of nature (the law of conservation of momentum);

educational:

learn how to prepare a workplace;

observe discipline;

to cultivate the ability to apply the acquired knowledge in the performance of independent tasks and the subsequent formulation of a conclusion;

to cultivate a sense of patriotism in relation to the work of Russian scientists in the field of movement of a body with a variable mass (jet propulsion) - K. E. Tsiolkovsky, S. P. Korolev;

developing:

to expand the horizons of students through the implementation of interdisciplinary connections;

develop the ability to correctly use physical terminology during frontal oral work;

form:

scientific understanding of the structure of the material world;

the universal nature of the acquired knowledge through the implementation of interdisciplinary connections;

methodical:

stimulate cognitive and creative activity;

to strengthen the motivation of students with the help of various teaching methods: verbal, visual and modern technical means, to create conditions for mastering the material.

As a result of studying the material in this lesson, the student should
know/understand :
- the meaning of the momentum of a material point, as a physical quantity;
- a formula expressing the relationship of momentum with other quantities (velocity, mass);
- classifying attribute of the impulse (vector value);
- units of impulse measurement;
- Newton's second law in impulsive form and its graphical interpretation; the law of conservation of momentum and the limits of its application;
- the contribution of Russian and foreign scientists who have had the greatest influence on the development of this branch of physics;

be able to:
- describe and explain the results of observations and experiments;
- give examples of the manifestation of the law of conservation of momentum in nature and technology;
- apply the acquired knowledge to solve physical problems on the application of the concept of "momentum of a material point", the law of conservation of momentum.

Pedagogical technologies:

advance learning technology;

technology of immersion in the topic of the lesson;

ICT.

Teaching methods:

verbal;

visual;

explanatory and illustrative;

heuristic;

problem;

analytical;

self-test;

mutual verification.

Conduct form: theoretical lesson.

Forms of organization of educational activities: collective, small groups, individual.

Interdisciplinary connections:

physics and mathematics;

physics and technology;

physics and biology;

physics and medicine;

physics and informatics;

Internal connections:

Newton's laws;

weight;

inertia;

inertia;

mechanical movement.

Equipment:

PC, screen,

blackboard, chalk,

balloon, inertial cars, water toy, aquarium with water, Segner's wheel model.

Equipment:

didactic:

reference notes for students, test tasks, reflection sheet;

methodical:

working programs a, calendar-thematic plan;

methodological guide for a teacher on the topic “ Pulse. Law of conservation of momentum. Examples of problem solving”;

Information Support:

PC with installed Windows OS and Microsoft Office package;

multimedia projector;

Microsoft PowerPoint presentations, videos:

- manifestation of the law of conservation of momentum in the collision of bodies;

- recoil effect;

Types of independent work:

auditorium: solving problems for the use of ZSI , work with the basic abstract;

extracurricular: work with abstracts, with additional literature .

Lesson progress:

I. Introduction

1. Organizational moment - 1-2 min.

a) checking those present, the readiness of students for the lesson, the availability of uniforms, etc.

2. Announcement of the topic, its motivation and goal setting - 5-6 min.

a) announcement of the rules of work in the lesson and the announcement of the assessment criteria;

b) e home task;

c) initial motivation of educational activity (involvement of students in the goal-setting process).

3. Actualization of basic knowledge (frontal survey) - 4-5 min.

II. Main part- 60min

1. Studying new theoretical material

a) Presentation of new lecture material according to the plan:

one). Definition of concepts: "momentum of the body", "impulse of force".

2). Solving qualitative and quantitative problems for calculating the momentum of a body, the momentum of a force, the masses of interacting bodies.

3). Law of conservation of momentum.

4). Limits of applicability of the momentum conservation law.

5). Algorithm for solving problems on the WSI. Particular cases of the momentum conservation law.

6). Application of the law of conservation of momentum in science, technology, nature, medicine.

b) Conducting demonstration experiments

c) Viewing a multimedia presentation.

d) Consolidation of the material in the course of the lesson (solving problems for the use of ZSI, solving qualitative problems);

e) Filling in the supporting abstract.

III. Control of assimilation of the material - 10 min.

IV. Reflection. Summing up - 6-7 minutes. (Time reserve 2 min.)

Preliminary preparation of students

Students are given the task to prepare a multimedia presentation and a message on the topics: "The law of conservation of momentum in technology", "The law of conservation of momentum in biology", "The law of conservation of momentum in medicine".

During the classes.

I. Introduction

1. Organizational moment.

Checking the absence and readiness of students for the lesson.

2. Announcement of the topic, its motivation and goal setting .

a) the announcement of the rules of work in the lesson and the announcement of the assessment criteria.

Rules for the lesson:

On your desktops are the reference notes that will be the main working element in today's lesson.

The reference outline indicates the topic of the lesson, the order in which the topic is studied.

In addition, today in the lesson we will use a rating system, i.e. each of you will try to earn as many points as possible with your work in the lesson, points will be awarded for correctly solved problems, correct answers to questions, correct explanation of observed phenomena, in total for the lesson you can score a maximum of 27 points, i.e. the correct, complete answer for each question 0.5 points, the solution of the problem is estimated at 1 point.

You will calculate the number of your points for the lesson yourself and write it down in the reflection card, so if you type from 19-27 points - "excellent"; from 12–18 points – “good” rating; from 5-11 points - "satisfactory" rating

b) homework:

Learn lecture material.

Collection of problems in physics, ed. A.P. Rymkevich No. 314, 315 (p. 47), No. 323,324 (p. 48).

v) initial motivation of educational activity (involvement of students in the goal-setting process):

I want to draw your attention to an interesting phenomenon, which we call impact. The effect produced by a blow has always aroused the surprise of a person. Why does a heavy hammer, placed on a piece of metal on an anvil, only press it against the support, while the same hammer flattens it with a hammer blow?

And what is the secret of the old circus trick, when a crushing hammer blow on a massive anvil does not harm the person on whose chest this anvil is installed?

Why can we easily catch a flying tennis ball with our hand, but we cannot catch a bullet without damage to the hand?

In nature, there are several physical quantities that can be conserved, we will talk about one of them today: this is momentum.

Impulse in translation into Russian means "push", "blow". This is one of the few physical quantities capable of being preserved during the interaction of bodies.

Please explain the observed phenomena:

EXPERIENCE #1: there are 2 toy cars on the demonstration table, No. 1 is at rest, No. 2 is moving, as a result of interaction, both cars change the speed of their movement - No. 1 gains speed, No. 2 - reduces the speed of their movement. (0.5 points)

EXPERIENCE #2: cars move towards each other, after a collision change the speed of their movement . (0.5 points)

What do you think: what is the purpose of our lesson today? What should we learn? (Suggested student response: to get acquainted with the physical quantity "momentum", learn how to calculate it, find the relationship of this physical quantity with other physical quantities.)(0.5 points)

3. Updating the knowledge complex.

You and I already know that if a body is acted upon by some force, then as a result of this ... .. (the body changes its position in space (performs a mechanical movement))

The answer to the question brings 0.5 points (maximum for the correct answers to all questions is 7 points)

Define mechanical motion.

Sample response: a change in the position of a body in space relative to other bodies is called mechanical motion.

What is a material point?

Sample response: a material point is a body whose dimensions can be neglected under the conditions of a given problem (the dimensions of the bodies are small compared to the distance between them, or the body travels a distance much greater than the geometric dimensions of the body itself)

-Give examples of material points.

Sample response: a car on the way from Orenburg to Moscow, a man and the moon, a ball on a long thread.

What is mass? Units of measurement in SI?

Sample response: mass is a measure of the inertia of a body, a scalar physical quantity, denoted by the Latin letter m, units of measurement in SI - kg (kilogram).

What does the expression: “the body is more inert”, “the body is less inert” mean?

Sample response: more inert - slowly changes speed, less inert - changes speed faster.

Give the definition of force, name the units of its measurement and the main

specifications.

Sample response: force - a vector physical quantity, which is a quantitative measure of the action of one body on another (a quantitative measure of the interaction of two or more bodies), characterized by a module, direction, point of application, measured in SI in Newtons (N).

-What powers do you know?

Sample response: gravity, elastic force, support reaction force, body weight, friction force.

As you understand: the resultant of the forces applied to the body is equal to

10 N?

Sample response: the geometric sum of the forces applied to the body is 10 N.

What will happen to a material point under the action of a force?

Sample response: the material point begins to change the speed of its movement.

How does the speed of a body depend on its mass?

Sample response: because mass is a measure of the inertia of a body, then a body of larger mass changes its speed more slowly, a body of smaller mass changes its speed faster.

What reference systems are called inertial?

Sample response: Inertial frames of reference are such frames of reference that move rectilinearly and uniformly or are at rest.

State Newton's first law.

Sample response: there are such frames of reference with respect to which translationally moving bodies keep their speed constant or are at rest if no other bodies act on them or the actions of these bodies are compensated.

- State Newton's third law.

\Sample response: the forces with which the bodies act on each other are equal in absolute value and directed along one straight line in opposite directions.

State Newton's second law.

where and speeds 1 and 2 balls before interaction, and - the speed of the balls after the interaction, and - masses of balls.

Substituting the last two equalities into the formula of Newton's third law and making transformations, we get:

, those.

The law of conservation of momentum is formulated as follows: the geometric sum of the impulses of a closed system of bodies remains constant for any interactions of the bodies of this system with each other.

Or:

If the sum of external forces is equal to zero, then the momentum of the system of bodies is conserved.

The forces with which the bodies of the system interact with each other are called internal, and the forces created by bodies that do not belong to this system are called external.

A system that is not acted upon by external forces, or the sum of external forces is equal to zero, is called closed.

In a closed system, bodies can only exchange impulses, while the total value of the impulse does not change.

Limits of application of the law of conservation of momentum:

Only in closed systems.

If the sum of the projections of external forces on a certain direction is equal to zero, then in the projection only on this direction it is possible to write: pini X = pcon X (the law of conservation of the momentum component).

If the duration of the interaction process is short, and the forces arising from the interaction are large (impact, explosion, shot), then during this short time the impulse of external forces can be neglected.

An example of a closed system along the horizontal direction is a cannon from which a shot is fired. The phenomenon of recoil (rollback) of a gun when fired. Firefighters experience the same impact when they direct a powerful jet of water at a burning object and hardly hold the hose.

Today you should learn the methods for solving qualitative and quantitative problems on this topic and learn how to apply them in practice.

Despite the fact that this topic is loved by many, it has its own peculiarities and difficulties. The main difficulty is that there is no single a universal formula that could be used in solving a particular problem on a given topic. In each task, the formula turns out to be different, and it is you who must obtain it by analyzing the condition of the proposed task.

In order to make it easier for you to solve problems correctly, I suggest using ALGORITHM FOR SOLVING PROBLEMS.

It does not need to be learned by heart, you can be guided by it, looking in a notebook, but as you solve problems, it will gradually be remembered by itself.

I want to warn you right away: I don’t consider problems without a picture, even solved correctly!

So, we will consider how, using the proposed PROBLEM SOLVING ALGORITHM, one should solve problems.

To do this, let's start with a step-by-step solution of the first task: (tasks in general)

Consider the Algorithm for solving problems on the application of the law of conservation of momentum. (slide with the algorithm, in the reference notes write to the drawings)

Algorithm for solving problems on the law of conservation of momentum:

Make a drawing on which to designate the directions of the coordinate axis, the velocity vectors of the bodies before and after the interaction;

2) Write in vector form the law of conservation of momentum;

3) Write down the momentum conservation law in projection onto the coordinate axis;

4) Express an unknown quantity from the resulting equation and find its value;

SOLUTION OF PROBLEMS (Special cases of ZSI for independent solution of problem No. 3):

(correct solution of 1 task - 1 point)

1. On a trolley weighing 800 kg, rolling along a horizontal track at a speed of 0.2 m/s, 200 kg of sand were poured on top.

What was the speed of the trolley after that?

2. A car with a mass of 20 tons moving at a speed 0.3 m / s, overtakes a wagon weighing 30 tons, moving at a speed of 0.2 m/s.

What is the speed of the wagons after the hitch has worked?

3. What speed will a cast-iron core lying on ice acquire if a bullet flying horizontally at a speed of 500 m / s bounces off it and moves in the opposite direction at a speed of 400 m / s? Bullet weight 10 g, core weight 25 kg. (the task is a backup, i.e. it is solved if there is time left)

(Problem solutions are displayed on the screen, students compare their solution with the standard, analyze errors)

Of great importance is the law of conservation of momentum for the study of jet propulsion.

Underjet propulsionunderstand the movement of the body that occurs when separating from the body with a certain speed of any part of it. As a result, the body itself acquires an oppositely directed momentum.

Inflate the rubber baby balloon without tying the holes, release it from your hands.

What will happen? Why? (0.5 points)

(Suggested answer: The air in the ball creates pressure on the shell in all directions. If the hole in the ball is not tied, then air will begin to escape from it, while the shell itself will move in the opposite direction. This follows from the law of conservation of momentum: the momentum of the ball before interaction is equal to zero, after interaction they must acquire impulses equal in magnitude and opposite in direction, i.e., move in opposite directions.)

The movement of the ball is an example of jet propulsion.

Video jet propulsion.

It is not difficult to make working models of jet engine devices.

In 1750, the Hungarian physicist J.A. Segner demonstrated his device, which was named the "Segner wheel" in honor of its creator.

A large "Segner wheel" can be made from a large milk bag: at the bottom of the opposite walls of the bag, you need to make a hole through the bag, piercing the bag with a pencil. Tie two threads to the top of the bag and hang the bag on some crossbar. Plug the holes with pencils and fill the bag with water. Then carefully remove the pencils.

Explain the observed phenomenon. Where can it be applied? (0.5 points)

(Suggested student answer: two jets will escape from the holes in opposite directions, and a reactive force will arise that will rotate the package. The Segner wheel can be used in a plant for watering flower beds or beds.)

Next model: spinning balloon. In an inflated children's balloon, before tying the hole with a thread, we insert a juice tube bent at a right angle into it. Pour water into a plate smaller than the diameter of the ball and lower the ball there so that the tube is on the side. The air will escape from the balloon and the balloon will begin to rotate on the water under the action of the reactive force.

OR: in an inflated children's balloon, before tying the hole with a thread, insert a juice tube bent at a right angle, hang the entire structure on the thread, when the air starts to exit the balloon through the tube, the balloon starts to rotate ..

Explain the observed phenomenon. (0.5 points)

Video "Jet propulsion"

Where does the law of conservation of momentum apply? Our guys will help us answer this question.

Student messages and presentations.

Topics of messages and presentations:

1. "Application of the law of conservation of momentum in technology and everyday life"

2. "Application of the Law of Conservation of Momentum in Nature".

3. "Application of the Law of Conservation of Momentum in Medicine"

Evaluation criteria:

The content of the material and its scientific character - 2 points;

Availability of presentation - 1 point;

Knowledge of the material and its understanding - 1 point;

Design - 1 point.

The maximum score is 5 points.

Let's now try to answer the following questions: (1 point for each correct answer, 0.5 points for an incomplete answer).

"It is interesting"

1. In one of the series of the cartoon "Well, you wait!" in calm weather, the wolf, in order to catch up with the hare, takes more air into his chest and blows into the sail. The boat accelerates and ... Is this phenomenon possible?

(Suggested student answer: No, because the wolf-sail system is closed, which means that the total momentum is zero, in order for the boat to move faster, an external force is necessary. Only external forces can change the momentum of the system. Wolf - air - internal force. )

2. The hero of the book by E. Raspe, Baron Munchausen, said: “Grabbing myself by the pigtail, I pulled it up with all my strength and without much difficulty pulled myself and my horse out of the swamp, which I tightly squeezed with both legs, like tongs.”

Is it possible to raise yourself in this way ?

(Suggested student answer: only external forces can change the momentum of a system of bodies, therefore, lift themselves in this way it is forbidden, because only internal forces act in this system. Before the interaction, the momentum of the system was zero. The action of internal forces cannot change the momentum of the system, therefore, after the interaction, the momentum will be zero).

3. There is an old legend about a rich man with a bag of gold, who, being on the absolutely smooth ice of the lake, froze, but did not want to part with his wealth. But he could have escaped if he had not been so greedy!

(Suggested student response: It was enough to push the bag of gold away from you, and the rich man himself would slide on the ice in the opposite direction according to the law of conservation of momentum.)

III. Control of assimilation of material:

Test tasks (Annex 1)

(Testing is carried out on sheets of paper, between which carbon paper is laid, at the end of testing one copy is for the teacher, the other is for the neighbor in the desk, mutual verification) (5 points)

IV. Reflection. Summarizing (Annex 2)

Concluding the lesson, I would like to say that the laws in physics can be applied to solving many problems. Today in the lesson you learned to put into practice one of the most fundamental laws of nature: the law of conservation of momentum.

I ask you to fill out the "Reflection" sheet, on which you can display the results of today's lesson.

List of used literature:

Literature for teachers

main:

Ed. Pinsky A.A., Kabardina O.F. Physics grade 10: a textbook for general education institutions and schools with in-depth study of physics: profile level. - M.: Enlightenment, 2013 .

Kasyanov V.A. Physics. Grade 10: textbook for general education studiesinstitutions. – M. : Bustard, 2012.

Physics 7-11. Library of visual aids. Electronic edition. M .: "Drofa", 2012

additional:

Myakishev G. Ya., Bukhovtsev B. B., Sotsky N. N. Physics-10: 15th edition. – M.: Enlightenment, 2006.

Myakishev G. Ya. Mechanics - 10: Ed. 7th, stereotype. – M.: Bustard, 2005.

Rymkevich A.P. Physics. Zadachnik-10 - 11: Ed. 10th, stereotype. – M.: Bustard, 2006.

Saurov Yu. A. Models of lessons-10: book. for the teacher. - M .: Education, 2005.

Kupershtein Yu. S. Physics-10: basic abstracts and differentiated problems. - St. Petersburg: September, 2004.

Used Internet resources

Literature for students:

Myakishev G.Ya. Physics. Grade 10: textbook for educational institutions: basic and specialized levels. - M.: Enlightenment, 2013 .

Gromov S.V. Physics-10.M. "Enlightenment" 2011

Rymkevich P.A. Collection of problems in physics. M .: "Drofa" 2012.

Annex 1

Option number 1.

1. Which of the following quantities is scalar?

A. mass.

B. body momentum.

B. strength.

2. A body of mass m moves at a speed. What is the momentum of the body?

A.

B. m

V.

3. What is the name of the physical quantity equal to the product of the force and the time of its action?

A. Body momentum.

B. Force projection.

B. Impulse of force.

4. In what units is the impulse of force measured?

A. 1 N s

B. 1 kg

B. 1 N

5. How is the momentum of the body directed?

A. Has the same direction as the force.

B. In the same direction as the speed of the body.

6. What is the change in the momentum of the body if a force of 15 N acts on it for 5 seconds?

A. 3 kg m/s

B. 20 kg m/s

H. 75 kg m/s

7. What is the name of the impact, in which part of the kinetic energy of the colliding bodies goes to their irreversible deformation, changing the internal energy of the bodies?

A. Absolutely inelastic impact.

B. Absolutely elastic impact

V. Central.

8. Which of the expressions corresponds to the law of conservation of momentum for the case of the interaction of two bodies?

A. = m

B.

V. m =

9. On what law is the existence of jet propulsion based?

A. Newton's first law.

B. The law of universal gravitation.

B. Law of conservation of momentum.

10. An example of jet propulsion is

A. The phenomenon of recoil when firing a weapon.

B. Combustion of a meteorite in the atmosphere.

B. Movement under the influence of gravity.

Annex 1

Option number 2.

1. Which of the following quantities is vector?

A. body momentum.

B. mass.

V. time.

2. What expression determines the change in body momentum?

A. m

B. t

V. m

3. What is the name of the physical quantity equal to the product of the mass of the body and the vector of its instantaneous velocity?

A. Force projection.

B. Impulse of force.

B. Impulse of the body.

4. What is the name of the unit of momentum of the body, expressed through the basic units of the International System?

A. 1 kg m/s

B. 1kg m/s 2

V. 1kg m 2 / s 2

5. Where is the change in the momentum of the body directed?

A. In the same direction as the speed of the body.

B. In the same direction as the force.

B. In the direction opposite to the movement of the body.

6. What is the momentum of a body with a mass of 2 kg moving at a speed of 3 m / s?

A. 1.5 kg m/s

B. 9 kg m/s

B. 6 kg m/s

7. What is the name of the impact, in which the deformation of the colliding bodies is reversible, i.e. disappears after termination of interaction?

A. Absolutely elastic impact.

B. Absolutely inelastic impact.

V. Central.

8. Which of the expressions corresponds to the law of conservation of momentum for the case of the interaction of two bodies?

A. = m

B.

V. m =

9. The law of conservation of momentum is fulfilled ...

A. Always.

B. Mandatory in the absence of friction in any reference systems.

B. Only in a closed system.

10. An example of jet propulsion is ...

A. The phenomenon of recoil when diving from a boat into the water.

B. The phenomenon of increasing body weight caused by accelerated movement

supports or suspension.

B. The phenomenon of attraction of bodies by the Earth.

Answers:

Option number 1

Option number 2

1. A 2. B 3. C 4. A 5. B 6. C 7. A 8. B 9. C 10. A

1 task - 0.5 points

Maximum when completing all tasks - 5 points

Annex 2

Basic outline.

Date ___________.

Theme of the lesson: “Momentum of the body. The Law of Conservation of Momentum.

1. The momentum of the body is __________________________________________________

2. Calculation formula for the momentum of the body: ________________________________

3. Units of measurement of body momentum: ___________________________________

4. The direction of the momentum of the body always coincides with the direction of ___________

5.Impulse of force - it __________________________________________________

6. Calculation formula for momentum of force :___________________________________

7. Units of measure momentum of force ___________________________________

8. The direction of the impulse of force always coincides with the direction ______________________________________________________________________

9. Write down Newton's second law in impulsive form:

______________________________________________________________________

10. Absolutely elastic impact is _______________________________________

______________________________________________________________________

______________________________________________________________________

11. Absolutely inelastic impact is _____________________________________

______________________________________________________________________

______________________________________________________________________

12. With a perfectly elastic impact, ____________________________ occurs

______________________________________________________________________

______________________________________________________________________

16. Mathematical record of the law: _______________________________________

17. Limits of applicability of the law of conservation of momentum:

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

18. Algorithm for solving problems on the law of conservation of momentum:

1)____________________________________________________________________

2)____________________________________________________________________

3)____________________________________________________________________

4)____________________________________________________________________

19. Particular cases of the law of conservation of momentum:

A) absolutely elastic interaction: Projection on the OX axis: 0.3 m/s, catches up with a car weighing 30 tons, moving at a speed of 0.2 m/s. What is the speed of the wagons after the hitch has worked?

____________

Answer:

21. Application of the law of conservation of momentum in technology and everyday life:

a) Jet propulsion is ___________________________________________ __________________________________________________________________________________________________________________________________________________________________________________________________________________Examples of jet propulsion: _____________________________________________________________________

_____________________________________________________________________

c) the phenomenon of recoil _____________________________________________________

____________________________________________________________________________________________________________________________________________

22. Application of the law of conservation of momentum in nature:

23. Application of the law of conservation of momentum in medicine:

______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

24. It's interesting:

1. There is an old legend about a rich man with a bag of gold, who, being on the absolutely smooth ice of the lake, froze, but did not want to part with his wealth. But he could have escaped if he had not been so greedy! How?__________________________________________________________________

__________________________________________________________________________________________________________________________________________________________________________________________________________________

2. In one of the series of the cartoon "Well, you wait!" in calm weather, the wolf, in order to catch up with the hare, takes more air into his chest and blows into the sail. The boat accelerates and ... Is this phenomenon possible? Why?

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. The hero of the book by E. Raspe, Baron Munchausen, said: “Grabbing myself by the pigtail, I pulled it up with all my might and without much difficulty pulled myself and my horse out of the swamp, which I tightly squeezed with both legs, like tongs.”

Is it possible to raise yourself in this way? Why?

___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Class grade ______________

Annex 3

Reflection sheet

Surname, name __________________________________________

Group________________________________________________

1. I worked at the lesson
2. With my work in the lesson, I
3. The lesson seemed to me
4. For the lesson I
5. My mood
6. The material of the lesson was

7. Homework seems to me

active / passive
satisfied (at) / not satisfied (at)
short / long
not tired / tired
got better / got worse
clear / not clear
useful / useless
interesting / boring
easy / difficult
interested / not interested

H draw your mood with a smiley.

Calculate the number of points received for the lesson, evaluate your work in the lesson.

If you typed:

from 19-27 points - "excellent" rating

From 12–18 points – “good” rating

From 5-11 points - rating "satisfactory"

I got (a) _________ points

Grade _________

body momentum is the quantity equal to the product of the mass of the body and its speed.

The momentum is denoted by a letter and has the same direction as the speed.

Pulse unit:

The momentum of the body is calculated by the formula: , where

The change in momentum of a body is equal to the momentum of the force acting on it:

For a closed system of bodies, law of conservation of momentum:

in a closed system, the vector sum of the momenta of the bodies before the interaction is equal to the vector sum of the momentum of the bodies after the interaction.

The law of conservation of momentum underlies jet propulsion.

Jet propulsion- this is the movement of the body that occurs after the separation of its part from the body.

To calculate the speed of a rocket, the law of conservation of momentum is written

and get the rocket speed formula: =, where M is the mass of the rocket,

10. Rutherford's experiments on the scattering of α-particles. Nuclear model of the atom. Bohr's quantum postulates.

The first model of the atom was proposed by the English physicist Thomson. According to Thomson, an atom is a positively charged ball containing negatively charged electrons.

Thomson's model of the atom was incorrect, which was confirmed in the experiments of the English physicist Rutherford in 1906.

In these experiments, a narrow beam of α-particles emitted by a radioactive substance was directed onto a thin gold foil. Behind the foil was placed a screen capable of glowing under the impact of fast particles.

It was found that most of the α-particles deviate from the rectilinear propagation after passing through the foil, i.e. dissipate. And some α-particles are generally thrown back.

Rutherford explained the scattering of α-particles by the fact that the positive charge is not distributed uniformly over the ball, as Thomson suggested, but is concentrated in the central part of the atom - atomic nucleus. When passing near the nucleus, an α-particle with a positive charge is repelled from it, and when it enters the nucleus, it is thrown back.

Rutherford suggested that the atom is arranged like a planetary system.

But Rutherford could not explain stability (why electrons do not radiate waves and fall towards a positively charged nucleus).

New ideas about the special properties of the atom were formulated by the Danish physicist Bohr in two postulates.

1st postulate. An atomic system can only be in special stationary or quantum states, each of which corresponds to its own energy; in a stationary state, the atom does not radiate.

2nd postulate. When an atom passes from one stationary state to another, a quantum of electromagnetic radiation is emitted or absorbed.

The energy of the emitted photon is equal to the difference between the energies of an atom in two states:

Planck's constant.

His movements, i.e. value .

Pulse is a vector quantity coinciding in direction with the velocity vector.

The unit of momentum in the SI system: kg m/s .

The impulse of a system of bodies is equal to the vector sum of the impulses of all bodies included in the system:

Law of conservation of momentum

If additional external forces act on the system of interacting bodies, for example, then in this case the relation is valid, which is sometimes called the law of change of momentum:

For a closed system (in the absence of external forces), the law of conservation of momentum is valid:

The action of the law of conservation of momentum can explain the phenomenon of recoil when shooting from a rifle or during artillery shooting. Also, the operation of the law of conservation of momentum underlies the principle of operation of all jet engines.

When solving physical problems, the law of conservation of momentum is used when knowledge of all the details of motion is not required, but the result of the interaction of bodies is important. Such problems, for example, are the problems of impact or collision of bodies. The law of conservation of momentum is used when considering the motion of bodies of variable mass, such as launch vehicles. Most of the mass of such a rocket is fuel. In the active phase of the flight, this fuel burns out, and the mass of the rocket rapidly decreases in this part of the trajectory. Also, the law of conservation of momentum is necessary in cases where the concept is inapplicable. It is difficult to imagine a situation where a motionless body acquires some speed instantly. In normal practice, bodies always accelerate and pick up speed gradually. However, when electrons and other subatomic particles move, the change in their state occurs abruptly without staying in intermediate states. In such cases, the classical concept of "acceleration" cannot be applied.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

EXAMPLE 3