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Mechanical movement. What is called mechanical motion: definition and formula

« Physics - 10th grade"

Based on the nature of the problems being solved, mechanics is divided into kinematics And dynamics.

Kinematics describes the movement of bodies without identifying the reasons causing this movement.

The first thing that catches your eye when observing the world around us is its variability. The world is not frozen, static. The changes in it are very diverse. But if we ask you what changes you notice most often, the answer will probably be clear: the position of objects changes(or bodies, as physicists say) relative to the ground and relative to each other over time.

Whether a dog is running or a car is racing, the same process occurs with them: their position relative to the ground and relative to you changes over time. They are moving. The spring compresses, the board on which you sat bends, and the position of various parts of the body relative to each other changes.

The change in the position of a body or parts of a body in space relative to other bodies over time is called mechanical movement.

The definition of mechanical motion looks simple, but this simplicity is deceptive. Read the definition again and think if all the words are clear to you: space, time, relative to other bodies. Most likely, these words require clarification.

Space and time.

Space and time are the most general concepts physics and... the least clear.

We do not have comprehensive information about space and time. But it is impossible to present the results that have been obtained today at the very beginning of the study of physics.

Usually it is quite enough for us to be able to measure the distance between two points in space using a ruler and time intervals using a clock. A ruler and a clock are the most important devices for measurements in mechanics, and in everyday life. Distances and time intervals have to be dealt with when studying many phenomena in all areas of science.

"...Regarding other bodies."

If this part of the definition of mechanical movement has escaped your attention, then you risk not understanding the most important thing. For example, in a carriage compartment there is an apple on the table. During the departure of the train, two observers (a passenger and a person accompanying them) are asked to answer the question: is the apple moving or not?

Each observer evaluates the position of the apple in relation to himself. The passenger sees that the apple is at a distance of 1 m from him and this distance remains the same over time. The person seeing you off on the platform sees how the distance from him to the apple increases over time.

The passenger replies that the apple does not undergo mechanical movement - it is motionless; the attendant says that the apple is moving.

Law of relativity of motion:
The nature of the movement of a body depends on which bodies we are considering this movement in relation to.

Let's start studying mechanical motion. It took humanity about two thousand years to take the right path, which ended with the discovery of the laws of mechanical motion.

The attempts of ancient philosophers to explain the causes of movement, including mechanical ones, were the fruit of pure fantasy. Just as, they reasoned, a weary traveler quickens his steps as he approaches his home, a falling stone begins to move faster and faster as it approaches mother earth. The movements of living organisms, such as cats, seemed in those days much simpler and more understandable than the fall of a stone. There were, however, some brilliant insights. Thus, the Greek philosopher Anaxagoras said that the Moon, if it did not move, would fall to the Earth, like a stone falling from a sling.

However, the true development of the science of mechanical motion began with the works of the great Italian physicist G. Galilei.

Kinematics is a branch of mechanics that studies methods of describing movements and the relationship between quantities that characterize these movements.

To describe the movement of a body means to indicate a way to determine its position in space at any moment in time.

Already at first glance, the task of description seems very difficult. In fact, look at the swirling clouds, the swaying leaves on a tree branch. Imagine the complex movement of the pistons of a car speeding along the highway. How to begin to describe the movement?

The simplest thing (and in physics we always go from simple to complex) is to learn to describe the movement of a point. A point can be understood, for example, as a small mark placed on a moving object - a soccer ball, a tractor wheel, etc. If we know how the movement of each such point (each very small section) of the body occurs, then we will know how the whole body moves.

However, when you say that you ran 10 km on skis, no one will specify which part of your body covered the distance of 10 km, although you are by no means a point. IN in this case this does not have any significant significance.

Let's introduce the concept material point- the first physical model of real bodies.

Material point- a body whose size and shape can be neglected under the conditions of the problem under consideration.

Reference system.

The motion of any body, as we already know, is relative motion. This means that the movement given body may be different in relation to other bodies. When studying the motion of a body that interests us, we must indicate in relation to which body this motion is being considered.

The body relative to which motion is considered is called body of reference.

To calculate the position of a point (body) relative to a selected reference body depending on time, you must not only associate a coordinate system with it, but also be able to measure time. Time is measured using a clock. Modern watches are complex devices. They allow you to measure time in seconds accurate to the thirteenth decimal place. Naturally, no mechanical watch can provide such accuracy. Thus, one of the most accurate mechanical clocks in the country on the Spasskaya Tower of the Kremlin is ten thousand times less accurate than the State Time Standard. If the reference clock is not adjusted, it will run away by one second or be three hundred thousand years behind. It is clear that in everyday life there is no need to measure time with very high accuracy. But for physical research, astronautics, geodesy, radio astronomy, management by air high precision in time measurement is simply necessary. The accuracy with which we can calculate the position of the body at any point in time depends on the accuracy of time measurement.

The set of reference body, associated coordinate system and clock is called reference system.

The figure shows the frame of reference chosen to consider the flight of a thrown ball. In this case, the body of reference is the house, the coordinate axes are chosen so that the ball flies at XOY plane, a stopwatch is used to determine the time.

Mechanical movement is a change in the position of a body in space relative to other bodies.

For example, a car is moving along the road. There are people in the car. People move along with the car along the road. That is, people move in space relative to the road. But relative to the car itself, people do not move. This shows relativity of mechanical motion. Next we will briefly consider main types of mechanical movement.

Forward movement- this is the movement of a body in which all its points move equally.

For example, the same car makes forward motion along the road. More precisely, only the body of the car performs translational motion, while its wheels perform rotational motion.

Rotational movement is the movement of a body around a certain axis. With such a movement, all points of the body move in circles, the center of which is this axis.

The wheels we mentioned perform rotational motion around their axes, and at the same time, the wheels perform translational motion along with the car body. That is, the wheel makes a rotational movement relative to the axis, and a translational movement relative to the road.

Oscillatory motion- This periodic motion, which occurs alternately in two opposite directions.

For example, oscillatory motion makes a pendulum in a clock.

Progressive and rotational movement– the most simple types mechanical movement.

Relativity of mechanical motion

All bodies in the Universe move, so there are no bodies that are at absolute rest. For the same reason, it is possible to determine whether a body is moving or not only relative to some other body.

For example, a car is moving along the road. The road is located on planet Earth. The road is still. Therefore, it is possible to measure the speed of a car relative to a stationary road. But the road is stationary relative to the Earth. However, the Earth itself revolves around the Sun. Consequently, the road along with the car also revolves around the Sun. Consequently, the car makes not only translational motion, but also rotational motion (relative to the Sun). But relative to the Earth, the car makes only translational motion. This shows relativity of mechanical motion.

Relativity of mechanical motion– this is the dependence of the trajectory of the body, the distance traveled, movement and speed on the choice reference systems.

Material point

In many cases, the size of a body can be neglected, since the dimensions of this body are small compared to the distance that this body moves, or compared to the distance between this body and other bodies. To simplify calculations, such a body can conventionally be considered a material point that has the mass of this body.

Material point is a body whose dimensions can be neglected under given conditions.

The car we have mentioned many times can be taken as a material point relative to the Earth. But if a person moves inside this car, then it is no longer possible to neglect the size of the car.

As a rule, when solving problems in physics, we consider the movement of a body as motion of a material point, and operate with such concepts as the speed of a material point, the acceleration of a material point, the momentum of a material point, the inertia of a material point, etc.

Frame of reference

A material point moves relative to other bodies. The body in relation to which the given is considered mechanical movement, is called the body of reference. Reference body are chosen arbitrarily depending on the tasks to be solved.

Associated with the reference body coordinate system, which is the reference point (origin). The coordinate system has 1, 2 or 3 axes depending on the driving conditions. The position of a point on a line (1 axis), plane (2 axes) or in space (3 axes) is determined by one, two or three coordinates, respectively. To determine the position of the body in space at any moment in time, it is also necessary to set the beginning of the time count.

Frame of reference is a coordinate system, a reference body with which the coordinate system is associated, and a device for measuring time. The movement of the body is considered relative to the reference system. In the same body, relatively different bodies counting in different systems coordinates can be completely different coordinates.

Trajectory of movement also depends on the choice of reference system.

Types of reference systems can be different, for example, a fixed reference system, a moving reference system, an inertial reference system, a non-inertial reference system.

article taken from the site av-physics.narod.ru

Organization of the class for the lesson

Introducing the lesson plan, articulating the purpose and objectives of the lesson.

Updating knowledge

“Today in the lesson we will get acquainted with movement, its types, as well as the concepts of trajectory, path, movement.”

Brainstorm

Situation for discussion in pairs

If we talk about an open field where a car is moving.

So can we tell where or where he is going?

Sample correct student answers

We can’t say for sure

There are no landmarks by which we could say: “he is coming from the bridge, or he is approaching the city.”

Consideration of examples of mechanical movement (slide No. 5)

Discussion of what we saw

Conclusion:

Yes, relative to the tree, the boy, the car, the plane change their location, that is, we can say that the boy, the car, the plane are moving relative to the tree.

Definition of mechanical movement

A change in the position of a body relative to other bodies over time is called mechanical motion.(write in notebook)

To understand the meaning of this definition we need to introduce the concept of a body of reference and the relativity of motion

Let's watch the video “Mechanical movement. Reference body"

Conclusion:

Reference body - this body, relative to which the position of another is determined body. Usually as bodies of reference the earth is selected, but there can also be an object moving relative to the earth: a car, a boat, an airplane, etc.

Students give examples of mechanical motion of bodies

What can you say about the body sizes involved in movement?

Approximate correct answer - They are all different in size

Speaking about sizes, we need to accept some conditions.

For this purpose, I suggest watching the video “Material Point”

A material point is a body whose size and shape can be neglected under given conditions.

Criteria for replacing a body with a material point:

a) the path traversed by the body is much more sizes moving body.

b) the body moves translationally.

Definition of translational motion

This is a movement in which a straight line segment connecting any two points of this body, the shape and dimensions of which do not change during movement, remains parallel to its position at any previous moment in time.

Question for students

How to determine body position? (discussion in pairs)

Conclusion after discussion

Reference system: reference body, coordinate system, clock.

The reference system can be:

One-dimensional, when the position of the body is determined by one coordinate

Two-dimensional, when the position of the body is determined by two coordinates

Three-dimensional, when the position of the body is determined by three coordinates.

Demonstration.

I have a toy wind-up car on my desk.

Let's demonstrate its movement

Thought experiment

Let us now imagine that a car leaves a village (point A) to a city (point B). In this case, the road along which he moves has the following form (we draw an imaginary line on the board). This line is called a trajectory.

A trajectory is a line along which a body moves.

The trajectory can be

And if we measure shortest distance between two points, then we get movement.

The length of the trajectory along which a body moves over a certain period of time is called a path.

You see that the movement and path are indicated by the letter S.

Both movement and path are measured in kilometers, meters, centimeters, decimeters. The SI base unit of distance is meters.

1 mm = 0.001 m, 1 dm = 0.1 m, 1 cm = 0.01 m, 1 km = 1000 m.

Checking understanding

Formative assessment (peer assessment)

Each task takes 4 minutes to complete; for assessment, one student reads out his answer, the rest are assessed using green (agree) and red (disagree) semaphore colors

Appendix 1

dAppendix 2 (material point, path, movement)

Think and answer

1. Is it possible to consider the Moon as a material point when calculating the distance from the Earth to the Moon; when measuring its diameter; when calculating the motion of a satellite around the Moon; upon landing spaceship on its surface; when determining the speed of its movement around the Earth?

A) man walking from home to work;

b) the person performs gymnastic exercises;

c) a person travels on a ship;

d) when measuring a person's height?

a) he runs from the middle of the field towards the opponent’s goal;

b) he takes the ball from the opponent;

c) he makes a pass to another player;

d) he argues with the judge;

d) does the doctor help him?

4. Do we pay for travel or transportation when traveling in a taxi, by plane, by boat, by train?

5. The boy threw the ball up and caught it again. Assuming that the ball rose to a height of 2.5 m, find the path and displacement of the ball.

Consolidation The concepts of “path” and “movement”

Appendix 2

Mechanical movement

1.Mechanical movement is...

1) Movement of mechanized devices

2) Movement of cars and planes

3) Change in body position relative to other bodies over time

4) Moving any bodies

2.What is a trajectory?

Choose one of 3 answer options:

1) This is a line indicating the direction of movement of the body

2) This is the line along which the body moves

3) This is the path traveled by the body during movement

3.Examples of mechanical motion are...

Select several of 4 answer options:

1) Running man

2) Falling stone

3) Current flowing through the wires

4) Mixing layers of liquid during the boiling process

4.In what units is distance traveled measured in the International System (SI)?

Choose one of 4 answer options:

1) In kilometers

2) In meters

3) In centimeters

4) In hectometers

Lesson summary

Teacher: Today in class we looked at mechanical movement and its physical characteristics

Mechanical movement is a change in the position of a body in space relative to other bodies.

For example, a car is moving along the road. There are people in the car. People move along with the car along the road. That is, people move in space relative to the road. But relative to the car itself, people do not move. This shows up. Next we will briefly consider main types of mechanical movement.

Forward movement- this is the movement of a body in which all its points move equally.

For example, the same car makes forward motion along the road. More precisely, only the body of the car performs translational motion, while its wheels perform rotational motion.

Rotational movement is the movement of a body around a certain axis. With such a movement, all points of the body move in circles, the center of which is this axis.

Oscillatory motion- This is a periodic movement that occurs alternately in two opposite directions.

For example, a pendulum in a clock performs an oscillatory motion.

Translational and rotational movements are the simplest types of mechanical movement.

Relativity of mechanical motion

All bodies in the Universe move, so there are no bodies that are at absolute rest. For the same reason, it is possible to determine whether a body is moving or not only relative to some other body.

Relativity of mechanical motion– this is the dependence of the trajectory of the body, the distance traveled, movement and speed on the choice reference systems.

Material point

Material point is a body whose dimensions can be neglected under given conditions.

The car we have mentioned many times can be taken as a material point relative to the Earth. But if a person moves inside this car, then it is no longer possible to neglect the size of the car.

Frame of reference

A material point moves relative to other bodies. The body in relation to which this mechanical movement is considered is called the body of reference. Reference body are chosen arbitrarily depending on the tasks to be solved.

Frame of reference is a coordinate system, a reference body with which the coordinate system is associated, and a device for measuring time. The movement of the body is considered relative to the reference system. The same body relative to different reference bodies in different coordinate systems can have completely different coordinates.

Trajectory of movement also depends on the choice of reference system.

Types of reference systems can be different, for example, a fixed reference system, a moving reference system, an inertial reference system, a non-inertial reference system.

TICKET No. 1

Mechanical movement. Relativity of motion. Reference system. Material point. Trajectory. Path and movement. Instant speed. Acceleration. Uniform and uniformly accelerated movement.

The mechanical movement of a body is the change in its position in space relative to other bodies over time.

The trajectory of the body, the distance traveled and the displacement depend on the choice of the reference system. In other words, mechanical motion is relative. The coordinate system, the reference body with which it is associated, and the indication of the origin of time form a reference system.

A body whose dimensions can be neglected under given conditions of motion is called a material point.

The line along which a point of the body moves is called the trajectory of movement. The length of the trajectory is called the distance traveled.

The vector connecting the starting and ending points of the trajectory is called displacement.

The instantaneous speed of translational motion of a body at time t is the ratio of a very small movement S to the small period of time during which this movement occurred:

υ=S/t υ =1 m/1 s=1 m/s

Movement with a constant speed in magnitude and direction is called uniform rectilinear movement.

When the speed of a body changes, the concept of acceleration of the body is introduced.

Acceleration is a vector quantity equal to the ratio of a very small change in the velocity vector to the small period of time during which this change occurred:

a= υ /t a=1 m/s 2

Motion with acceleration that is constant in magnitude and direction is called uniformly accelerated:

With what force does a magnetic field with B=1.5 T act on a conductor with a length of l=0.03 m, located perpendicular to the magnetic field? Current I=2 A


	=90 0 Sin90 0 =1

	F=21.5310 -2 =910 -2 H

TICKET No. 2

Interaction of bodies. Strength. Newton's second law.

The reason for a change in the speed of movement of a body is always its interaction with other bodies. After turning off the engine, the car gradually slows down and stops. The main reason for changes in vehicle speed is the interaction of its wheels with the road surface. In physics, the concept of “force” is introduced to quantitatively express the action of one body on another. Examples of forces:
forces of elasticity, gravity, gravity, etc.

Force is a vector quantity, it is denoted by the symbol F. The direction of the force vector is taken to be the direction of the acceleration vector of the body on which the force acts. In the SI system:

F=1 H=1 kg*m/s 2

Newton's 2nd law:

The force acting on a body is equal to the product of the mass of the body and the acceleration imparted by this force:

The meaning of the law is that the force acting on a body determines the change in the speed of the body, and not the speed of movement of the body.

Laboratory work “Measuring the refractive index of glass”

TICKET No. 3

Body impulse. Law of conservation of momentum. Manifestation of the law of conservation of momentum in nature and its use in technology.

There is a physical quantity that changes equally for all bodies under the action of the same forces, if the time of action of the force is the same.

The quantity equal to the product of the mass of a body and the speed of its movement is called the momentum of the body or momentum.

The change in the momentum of the body is equal to the impulse of the force causing this change.

A physical quantity equal to the product of force F by the time t of its action is called impulse of force.

The momentum of a body is a quantitative characteristic of the translational motion of bodies. The unit of measurement of body impulse is: kg*m/s.

Law of conservation of momentum:

In a closed system, the geometric sum of the momenta of the bodies remains constant for any interaction of the bodies of this system with each other:

m 1 υ 1 +m 2 υ 2 =m 1 υ 1 I + m 2 υ 2 I

where υ 12, υ 12 I are the velocities of the first and second bodies before and after interaction.

A system of bodies that do not interact with other bodies not included in this system is called a closed system.

The law of conservation of momentum manifests itself in inertial reference systems (i.e., in those in which the body, in the absence of external influences, moves rectilinearly and uniformly). This law is used in technology: jet engine. When fuel burns, gases heated to a high temperature are ejected from the rocket nozzle at speed. The rocket begins to move as a result of this interaction and in accordance with this law.

M – rocket mass

υ – rocket speed

m – fuel mass

U is the speed of burned and ejected fuel.

A battery with an emf of 6 V and an internal resistance of r = 0.1 Ohm powers an external circuit with R = 11.9 Ohm. How much heat will be released in 10 minutes in the entire circuit?

	Q=I 2 Zt, where Z is the total resistance



	Q= 2 (R+r)t / (R+r) 2
	Q= 2 *t / (R+r)
	Q=36*600 / 12=1800 J

TICKET No. 4

The law of universal gravitation. Gravity. Body weight. Weightlessness.

Newton proved that the movement and interaction of the planets of the solar system occurs under the influence of a gravitational force directed towards the Sun and decreasing in inverse proportion to the square of the distance from it. All bodies in the Universe mutually attract each other.

Newton called the force of mutual attraction between bodies in the Universe the force of universal gravitation. In 1682, Newton discovered the law of universal gravitation:

All bodies attract each other. The force of universal gravitation is directly proportional to the product of the masses of bodies and inversely proportional to the square of the distance between them:

F=G*m 1 *m 2 / R 2

G is the gravitational constant.

The force of attraction exerted by the Earth on all bodies is called gravity:

This force decreases in inverse proportion to the square of the distance from the center of the Earth.

In technology and everyday life, the concept of body weight is widely used - P

The weight of a body is the force with which the body, due to its attraction to the Earth, acts on a horizontal support or suspension.

The weight of a body on a stationary or uniformly moving horizontal support is equal to the force of gravity, but they are applied to different bodies.

During accelerated motion, the weight of a body, the direction of acceleration of which coincides with the direction of acceleration of free fall, is less than the weight of the body at rest.

If a body, together with a support, falls freely and the acceleration of the body is equal to the acceleration of free fall, and their directions coincide, then the weight of the body disappears. This phenomenon is called weightlessness:

A=g P=0 weightlessness

At what temperature is the internal energy 20 kg. Argon will be 1.25*10 6 J?

TICKET No. 5

Energy conversion during mechanical vibrations. Free and forced vibrations. Resonance.

In nature and technology, a type of mechanical movement occurs - oscillation.

Mechanical vibration is the movement of a body that is repeated exactly or approximately at equal intervals of time.

The forces acting between bodies within a system are called internal. Forces acting from outside the system on the bodies of this system are called external.

Free vibrations are vibrations that occur under the influence of internal forces. Oscillations under the influence of external periodically changing forces are called forced.

When the pendulum deviates from the equilibrium position, its potential energy increases, because the distance from the Earth's surface increases. When moving towards the equilibrium position, the speed of the pendulum increases, its kinetic energy increases due to a decrease in the potential reserve, as a result of a decrease in the distance from the Earth's surface. At equilibrium, kinetic energy is at its maximum and potential energy is at its minimum. After passing the equilibrium position, the kinetic energy is converted into potential energy, the speed of the pendulum decreases and at maximum deviation becomes equal to zero. In this way, a periodic transformation of energy occurs. But because When moving, bodies interact with other bodies, so part of the mechanical energy is converted into internal energy of thermal motion of atoms and molecules. The amplitude of the oscillations will decrease and after some time the pendulum will stop. Free oscillations are always damped.

In a system, when oscillations are excited under the influence of a periodically changing external force, the amplitude, at first, gradually increases. After some time, oscillations are established with a constant amplitude and a period equal to the period of the external force.

The amplitude also depends on the frequency of force changes. Provided that the frequency of the external force ν coincides with the natural frequency of the system ν 0, the amplitude has a maximum value.

Resonance is a sharp increase in the amplitude of forced oscillations as the frequency of change of the external force acting on the system approaches the frequency of free oscillations. The less friction in the system, the more pronounced the resonance (in Fig. Curve No. 1).

Laboratory work “Determination of the focal length of a collecting lens.”

TICKET No. 6

Experimental substantiation of the main provisions of the molecular kinetic theory of the structure of matter. Mass and size of molecules. Avogadro's constant.

At the beginning of the 19th century, the English scientist D. Dalton showed that many natural phenomena can be explained using the molecular structure of matter. By the beginning of the 20th century, the molecular kinetic theory of matter was finally created and confirmed by experiments. Main provisions of the ICT:

substances consist of molecules between which there are intermolecular intervals.

Molecules move continuously and chaotically.

At short distances between molecules and atoms, both attractive and repulsive forces act. The nature of these forces is electromagnetic.

Chaotic motion is also called thermal, because. it depends on temperature.

Experimental justification:

The fact that substances consist of molecules has been proven by photographs taken using electron microscope. The photographs show the arrangement of the molecules.

The fact that molecules are constantly moving is proven by Brown's experiment. In 1827, he observed how grains of clay moved in water. I couldn't explain. Brownian motion is the movement of clay grains caused by the impacts of chaotically moving water molecules. And another natural phenomenon - diffusion, proves the continuous movement of molecules. Diffusion is the phenomenon of penetration of molecules of one substance into the molecules of another substance. Even in solids, where this penetration process occurs most slowly, diffusion is still observed. For example: a gold plate lies on a lead plate. They are under load. After some time, a molecule of each substance will be discovered in the adjacent contacting body.

3. The fact that molecules are attracted to each other is proven by experience with lead cylinders. They can withstand weight up to 5 kg. Diffusion also proves that molecules interact in solids.

Both repulsive and interaction forces act simultaneously between molecules. They are magnetic in nature. During deformations in solid bodies, forces manifest themselves in the form of elastic forces and determine the strength of the bodies. These forces act over very short distances - within the size of molecules. But the effect will be observed if the molecules are brought closer to a distance greater than their stable equilibrium (when the two types of forces are equal in value), then the repulsive forces will increase and the attraction will decrease.

Experimental studies have shown that the molecules are very small. For example: the mass of an olive oil molecule m 0 = 2.5 * 10 -26 kg, and the size of the molecule d = 3 * 10 -10 m.

Avogadro's number is the number of atoms contained in 0.012 kg of the carbon isotope 12 C. Named after the Italian scientist of the 19th century.

N A =6.02*10 23 mol -1

During the electrolysis of a solution of copper sulfate, work was done

A=1.4*10 7 J. Determine the amount of copper released if the voltage between the electrodes of the bath is U=6 V.

K=3.29*10 -7 J


	m=kA / U m=3.2910 -7 1.410 7 / 6=4.6 / 6=0.76 kg

TICKET No. 7

Ideal gas. The main MCT equation for an ideal gas. Temperature and its measurement. Absolute temperature.

In real life, when studying phenomena in nature and technology, it is impossible to take into account all the factors influencing it. For this reason, one can take into account most important factor, for example, the movement of molecules, while others (interactions) are not taken into account. On this basis, a model of the phenomenon is introduced.

Gas molecules hitting the surface of a body or the wall of a vessel exert pressure –P. Pressure depends on the following factors:

from the kinetic energy of molecular motion. The larger it is, the greater the pressure;

number of molecules per unit volume. The more there are, the greater the pressure.

Basic equation ideal gas can be written as a formula:

P=n*m 0 *υ 2 /3 or P=2*n*E/3

Where n is the concentration of molecules per unit volume (n=N/V), m 0 is the mass of one molecule, E is the average value of the kinetic energy of movement of molecules, υ 2 is the average value of the square of the speed of kinetic movement of molecules.

The pressure of an ideal gas is directly proportional to the average kinetic energy of the translational motion of its molecules and the number of molecules per unit volume. Pressure is measured in Pascals P=Pa. Conditions close to an ideal gas are created in vacuum tubes and devices. A vacuum is created there, because gas molecules are a hindrance - the lamp filament will oxidize and burn out instantly.

Temperature is a quantity characterizing the degree of heating of a body. In order to measure body temperature, a device was created - a thermometer. A hydrogen thermometer was chosen as a reference, in which discharged hydrogen was used as a substance. It expands when heated in the same way as oxygen, nitrogen, etc. A closed vessel with discharged hydrogen was connected to a manometer (a device for measuring pressure) and by increasing the temperature, the gas expanded, thereby changing its pressure. Pressure and temperature are related linearly, so the temperature could be determined from the pressure gauge reading. The temperature scale established by a hydrogen thermometer is called the Celsius scale. The melting temperature of ice at normal temperatures is taken as 0 0 C atmospheric pressure, and beyond 100 0 C is the boiling point of water, also at normal pressure 1. Another construction of the temperature scale is also possible. For a deeper understanding of the physical meaning of phenomena, Kelvin proposed another scale - the thermodynamic one. Now it is called the Kelvin scale. It takes –273 0 C as the starting point. This value is called absolute zero - the temperature at which the translational movement of molecules stops. It does not occur in nature below temperatures. Temperature on this scale is called absolute temperature and is measured in Kelvin - TK.

The speed of molecular movement depends on temperature, so temperature is said to be a measure of the kinetic energy of molecular movement. With increasing temperature, the average speed of translational motion of molecules also increases.

E=3*k*T/2 P=nkT Where k is Boltzmann’s constant =1.38*10 -23 J/K

An electrical diagram is given. Determine the resistance of four conductors with the same resistance R 1-4 = 4 Ohms, connected to each other according to the diagram:

Conductors 1,4 are connected in series, and 2,3 in parallel.

Let's find the total resistance of conductors 2.3:

R 23 =R / n R 23 = 4 / 2 = 2 Ohm.

Find the total resistance of the entire circuit:

R=R 1 +R 23 +R 4 R=4+2+4=10 Ohm.

TICKET No. 8

Equation of state of an ideal gas (Mendeleev-Clapeyron equation). Isoprocesses.

In real life, when studying phenomena in nature and technology, it is impossible to take into account all the factors influencing it. For this reason, it is possible to take into account the most important factor, such as the movement of molecules, while others (interaction) are not taken into account. On this basis, a model of the phenomenon is introduced.

An ideal gas is a model of a real gas. This is a gas whose molecular sizes are small compared to the volume of the vessel and they practically do not interact.

Physical quantities, the value of which is determined by the joint action of a huge number of molecules, are called thermodynamic parameters: P, V, T.

An ideal gas is described by the following parameters that are included in the Mendeleev-Clapeyron equation: PV = m*R*T/ M

where M is the molar mass of the substance, R is the universal gas constant, does not depend on the nature of the gas = 8.31 N*m/Kmol*K, m is the mass of the gas.

An isoprocess is a process in which the mass of a gas and one of its parameters remain constant.

Determine the red limit of the photoelectric effect for a metal with work function A = 3.2 * 10 -19 J.

TICKET No. 9

Evaporation and condensation. Saturated and unsaturated pairs. Air humidity. Air humidity measurement.

Substances pass from one state to another. During chaotic movement, some water molecules with high kinetic energy leave it. At the same time, they overcome the forces of attraction from other molecules. This process is called evaporation. (see poster). But another process can also be observed when the vapor molecules return to the liquid, this process is called condensation. If there is an air flow above the vessel, it carries away vapor molecules and the evaporation process occurs faster. The evaporation process also accelerates when the temperature of the liquid increases.

If the vessel is covered with a lid, then after some time a dynamic equilibrium will be established - the number of molecules leaving the liquid = the number of molecules returning to the liquid.

Vapor that is in dynamic equilibrium with its liquid is called saturated. Even if we begin to compress saturated steam at a constant temperature, initially the equilibrium will be disrupted, but then the concentration of steam molecules will level out again, as in dynamic equilibrium.

Saturated vapor pressure P 0 does not depend on volume at constant temperature.

On Earth there is a continuous formation of water vapor: evaporation from water bodies, vegetation, vapor exhaled by animals. But this water vapor is not saturated, because air masses move in the atmosphere.

Humidity is the amount of water vapor in the Earth's atmosphere.

Water vapor - humidity - is characterized by parameters. (further see the office posters and tell us about them).

Relative humidity can be measured with several instruments, but let's consider one - a psychrometer. (Further about the device and method of measurement, refer to the posters).

Laboratory work “Measuring the wavelength of light using a diffraction grating.”

TICKET No. 10

Crystalline and amorphous bodies. Elastic and plastic deformations of solids.

Crystals surround us everywhere. Solids all refer to crystals. But because Since single crystals do not occur in nature, we do not see them. Most often, substances consist of many interlocking crystalline grains - polycrystals. In crystalline bodies, the atoms are arranged in a strict order and form a spatial crystal lattice. As a result, they have a regular external shape. Examples of crystalline bodies: table salt, snowflake, mica, graphite, etc. These bodies have certain properties - graphite writes well in layers, salt breaks with flat edges, mica exfoliates in the longitudinal direction. T. ob. they have the same physical properties in one direction - called anisotropy. In reality, most often anisotropy is not observed, because the body consists of a large number of chaotically fused crystals, the total effect of anisotropy leads to the elimination of this phenomenon. But there are other bodies that do not consist of crystals, i.e. they do not have a crystal lattice, they are called amorphous. They have the properties of elastic and liquid bodies. When hit, they prick, and at high temperatures they flow. Examples of amorphous bodies: glass, plastics, resin, rosin, sugar candy. They have the same physical properties in all directions - called. isotropy.

An external mechanical effect on a body causes a displacement of atoms from equilibrium positions and leads to a change in the shape and volume of the body, i.e. to its deformation. The simplest types of deformation are tension and compression. Cables of cranes, cable cars, towing cables, and strings of musical instruments experience tension. The walls and foundations of buildings are subject to compression. Deformation can be characterized by absolute elongation ∆l = l 2 -l 1, where l 1 is before stretching, l 2 is after it. And the ratio of absolute elongation to the length of the sample is called relative elongation: ε=∆l / l 1. When a body deforms, elastic forces arise. The physical quantity equal to the ratio of the modulus of the elastic force to the cross-sectional area of the body is called stress σ=F/S. At small deformations, Hooke's law is satisfied, when the deformation increases proportionally with increasing force on the body. But only up to a certain strength limit. If the stress is increased and after its removal the dimensions of the body are still fully restored, then such deformation is called elastic, otherwise it is called residual or plastic.

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