In the world around us, there are various kinds of physical phenomena that are directly related to change in body temperature. Since childhood, we know that cold water, when heated, first becomes barely warm and only after a certain time hot.
With such words as “cold”, “hot”, “warm”, we define different degrees of “heating” of bodies, or, speaking in the language of physics, different temperatures of bodies. The temperature of warm water is slightly higher than the temperature of cool water. If we compare the temperature of summer and winter air, the difference in temperature is obvious.
Body temperature is measured with a thermometer and is expressed in degrees Celsius (°C).
As is known, diffusion at a higher temperature is faster. From this it follows that the speed of movement of molecules and temperature are deeply interconnected. If you increase the temperature, then the speed of movement of molecules will increase, if you decrease it, it will decrease.
Thus, we conclude: body temperature is directly related to the speed of movement of molecules.
Hot water consists of exactly the same molecules as cold water. The difference between them is only in the speed of movement of molecules.
Phenomena that are related to the heating or cooling of bodies, a change in temperature, are called thermal. These include heating or cooling air, melting metal, melting snow.
Molecules or atoms, which are the basis of all bodies, are in endless chaotic motion. The number of such molecules and atoms in the bodies around us is enormous. A volume equal to 1 cm³ of water contains approximately 3.34 x 10²² molecules. Any molecule has a very complex trajectory of motion. For example, gas particles moving at high speeds in different directions can collide both with each other and with the walls of the vessel. Thus, they change their speed and continue moving again.
Figure #1 shows the random movement of paint particles dissolved in water.
Thus, we make one more conclusion: the chaotic movement of the particles that make up bodies is called thermal motion.
Randomness is the most important feature of thermal motion. One of the most important evidence for the movement of molecules is diffusion and Brownian motion.(Brownian motion is the movement of the smallest solid particles in a liquid under the influence of molecular impacts. As observation shows, Brownian motion cannot stop).
In liquids, molecules can oscillate, rotate, and move relative to other molecules. If we take solids, then in them the molecules and atoms vibrate around some average positions.
Absolutely all molecules of the body participate in the thermal motion of molecules and atoms, which is why with a change in thermal motion the state of the body itself, its various properties, also change. Thus, if you increase the temperature of the ice, it begins to melt, while taking on a completely different form - the ice becomes a liquid. If, on the contrary, the temperature of, for example, mercury is lowered, then it will change its properties and turn from a liquid into a solid.
T 
body temperature directly depends on the average kinetic energy of the molecules. We draw an obvious conclusion: the higher the temperature of the body, the greater the average kinetic energy of its molecules. Conversely, as the body temperature decreases, the average kinetic energy of its molecules decreases.
If you have any questions or want to learn more about thermal motion and temperature, register on our website and get the help of a tutor.
Do you have any questions? Don't know how to do your homework?
To get help from a tutor -.
The first lesson is free!
blog.site, with full or partial copying of the material, a link to the source is required.
To study the topic "Thermal motion" we need to repeat:
In the world around us, various kinds of physical phenomena occur, which are directly related to changes in the temperature of bodies.
Since childhood, we remember that the water in the lake is cold at first, then barely warm, and only after a while becomes suitable for swimming.
With such words as “cold”, “hot”, “slightly warm”, we define different degrees of “heatedness” of bodies, or, in the language of physics, different temperatures of bodies.
If we compare the temperature in the lake in summer and late autumn, the difference is obvious. The temperature of warm water is slightly higher than the temperature of ice water.
As is known, diffusion at a higher temperature is faster. From this it follows that the speed of movement of molecules and temperature are deeply interconnected.
Experiment: Take three glasses and fill them with cold, warm and hot water, and now put a tea bag in each glass and observe how the color of the water changes? Where will this change take place most intensively?
If you increase the temperature, then the speed of movement of molecules will increase, if you decrease it, it will decrease. Thus, we conclude: body temperature is directly related to the speed of movement of molecules.
Hot water consists of exactly the same molecules as cold water. The difference between them is only in the speed of movement of molecules.
Phenomena that are related to the heating or cooling of bodies, a change in temperature, are called thermal. These include heating or cooling not only liquid bodies, but also gaseous and solid air.
Other examples of thermal phenomena: metal melting, snow melting.
Molecules or atoms, which are the basis of all bodies, are in endless chaotic motion. The movement of molecules in different bodies occurs in different ways. Molecules of gases randomly move at high speeds along a very complex trajectory.Colliding, they bounce off each other, changing the magnitude and direction of the velocities.
Liquid molecules oscillate around equilibrium positions (because they are located almost close to each other) and relatively rarely jump from one equilibrium position to another. The movement of molecules in liquids is less free than in gases, but more free than in solids.
In solids, molecules and atoms oscillate around certain average positions.
As the temperature rises, the speed of the particles increases, That's why the chaotic motion of particles is usually called thermal.
Interesting:
What is the exact height of the Eiffel Tower? And it depends on the ambient temperature!
The fact is that the height of the tower fluctuates by as much as 12 centimeters.
and the temperature of the beams can reach up to 40 degrees Celsius.
And as you know, substances can expand under the influence of high temperature.
Randomness is the most important feature of thermal motion. One of the most important evidence for the movement of molecules is diffusion and Brownian motion. (Brownian motion is the movement of the smallest solid particles in a liquid under the influence of molecular impacts. As observation shows, Brownian motion cannot stop). Brownian motion was discovered by the English botanist Robert Brown (1773-1858).
Absolutely all molecules of the body participate in the thermal motion of molecules and atoms, which is why with a change in thermal motion the state of the body itself, its various properties, also change.
Consider how the properties of water change with temperature.
Body temperature directly depends on the average kinetic energy of molecules. We draw an obvious conclusion: the higher the temperature of the body, the greater the average kinetic energy of its molecules. Conversely, as the body temperature decreases, the average kinetic energy of its molecules decreases.
Temperature - a value that characterizes the thermal state of the body or otherwise a measure of the "heating" of the body.
The higher the temperature of a body, the more energy its atoms and molecules have on average.
Temperature is measured thermometers, i.e. temperature measuring instruments
The temperature is not directly measured! The measured value depends on the temperature!
Currently, there are liquid and electrical thermometers.
In modern liquid thermometers, this is the volume of alcohol or mercury. The thermometer measures its own temperature! And, if we want to measure the temperature of some other body with a thermometer, we must wait some time until the temperatures of the body and the thermometer are equal, i.e. thermal equilibrium will come between the thermometer and the body. A home thermometer "thermometer" needs time to give an accurate value for the patient's temperature.
This is the law of thermal equilibrium:
for any group of isolated bodies, after some time, the temperatures become the same,
those. a state of thermal equilibrium occurs.
Body temperature is measured with a thermometer and is most often expressed in terms of degrees Celsius(°C). There are also other units of measurement: Fahrenheit, Kelvin and Réaumur.
Most physicists measure temperature on the Kelvin scale. 0 degrees Celsius = 273 degrees Kelvin
1. In 1827, the English botanist R. Brown, studying pollen particles suspended in water with a microscope, noticed that these particles move randomly; they seem to tremble in the water.
The reason for the movement of pollen particles could not be explained for a long time. Brown himself suggested in the beginning that they move because they are alive. They tried to explain the movement of particles by unequal heating of different parts of the vessel, chemical reactions taking place, etc. Only much later did they understand the true cause of the movement of particles suspended in water. This reason is the movement of molecules.
The water molecules in which the pollen particle is located move and hit it. In this case, an unequal number of molecules hits the particle from different sides, which leads to its movement.
Let at the moment of time \ (t_1 \) under the influence of impacts of water molecules, the particle moved from point A to point B. At the next point in time, a larger number of molecules hit the particle from the other side, and the direction of its movement changes, it moves from t. In t. C. Thus, the movement of a particle of pollen is a consequence of the movement and impacts of water molecules on it, in which the pollen is located (Fig. 65). A similar phenomenon can be observed if particles of paint or soot are placed in water.
Figure 65 shows the trajectory of a pollen particle. It can be seen that it is impossible to speak of any particular direction of its movement; it changes all the time.
Since the motion of a particle is a consequence of the motion of molecules, we can conclude that molecules move randomly (chaotically). In other words, it is impossible to single out any particular direction in which all molecules move.
The movement of molecules never stops. It can be said that it continuously. The continuous random movement of atoms and molecules is called thermal motion. This name is determined by the fact that the speed of movement of molecules depends on the temperature of the body.
Since bodies consist of a large number of molecules and the movement of molecules is random, it is impossible to say exactly how many impacts this or that molecule will experience from others. Therefore, they say that the position of the molecule, its speed at each moment of time random. However, this does not mean that the movement of molecules does not obey certain laws. In particular, although the velocities of the molecules at some point in time are different, most of them have velocities close to some definite value. Usually, when speaking about the speed of movement of molecules, they mean average speed\((v_(cp)) \) .
2. From the point of view of the movement of molecules, one can explain such a phenomenon as diffusion.
Diffusion is the phenomenon of the penetration of molecules of one substance into the gaps between the molecules of another substance.
We smell perfume at some distance from the bottle. This is due to the fact that the molecules of spirits, like the molecules of air, move. There are gaps between molecules. Perfume molecules penetrate into the gaps between air molecules, and air molecules into the gaps between perfume molecules.
Diffusion of liquids can be observed if a solution of copper sulfate is poured into a beaker, and water is poured on top so that there is a sharp boundary between these liquids. After two or three days, you will notice that the border will no longer be so sharp; in a week it will be completely washed out. After a month, the liquid will become homogeneous and will be colored the same throughout the vessel (Fig. 66).
In this experiment, the molecules of copper sulphate penetrate into the gaps between the molecules of water, and the molecules of water - into the gaps between the molecules of copper sulphate. It should be borne in mind that the density of copper sulfate is greater than the density of water.
Experiments show that diffusion in gases occurs faster than in liquids. This is due to the fact that gases have a lower density than liquids, i.e. gas molecules are located at large distances from each other. Diffusion occurs even more slowly in solids, since the molecules of solids are even closer to each other than the molecules of liquids.
In nature, technology, everyday life, you can find many phenomena in which diffusion is manifested: staining, gluing, etc. Diffusion is of great importance in human life. In particular, due to diffusion, oxygen enters the human body not only through the lungs, but also through the skin. For the same reason, nutrients pass from the intestines into the blood.
The diffusion rate depends not only on the state of aggregation of the substance, but also on temperature.
If you prepare two vessels with water and blue vitriol for a diffusion experiment, and put one of them in the refrigerator and leave the other in the room, you will find that at a higher temperature, diffusion will occur faster. This is because as the temperature rises, the molecules move faster. Thus, the speed of the molecules
and body temperature are related.
The greater the average speed of movement of the body's molecules, the higher its temperature.
3. Molecular physics, unlike mechanics, studies systems (bodies) consisting of a large number of particles. These bodies may be in different states.
The quantities characterizing the state of the system (body) are called state parameters. The parameters of the state include pressure, volume, temperature.
Such a state of the system is possible, in which the parameters characterizing it remain unchanged for an arbitrarily long time in the absence of external influences. This state is called thermal equilibrium.
So, the volume, temperature, pressure of a liquid in a vessel that is in thermal equilibrium with the air in the room do not change if there are no external reasons for this.
4. The state of thermal equilibrium of the system characterizes such a parameter as temperature. Its peculiarity is that the temperature value in all parts of the system, which is in a state of thermal equilibrium, is the same. If you lower a silver spoon (or a spoon made of any other metal) into a glass of hot water, the spoon will heat up and the water will cool. This will happen until thermal equilibrium is reached, at which the spoon and water will have the same temperature. In any case, if we take two differently heated bodies and bring them into contact, then the hotter body will cool down, and the colder one will heat up. After some time, the system consisting of these two bodies will come into thermal equilibrium, and the temperature of these bodies will become the same.
So, the temperature of the spoon and water will become the same when they come into thermal equilibrium.
Temperature is a physical quantity that characterizes the thermal state of a body.
So, the temperature of hot water is higher than cold; In winter, the air temperature outside is lower than in summer.
The temperature unit is degree Celsius (°C). Temperature is measured thermometer.
The device of a thermometer and, accordingly, the method of measuring temperature is based on the dependence of the properties of bodies on temperature, in particular, the property of a body to expand when heated. Different bodies can be used in thermometers: both liquid (alcohol, mercury), and solid (metals) and gaseous. They are called thermometric bodies. A thermometric body (liquid or gas) is placed in a tube equipped with a scale, it is brought into contact with the body whose temperature is to be measured.
When constructing the scale, two main (reference, reference) points are selected, to which certain temperature values are assigned, and the interval between them is divided into several parts. The value of each part corresponds to the temperature unit on this scale.
5. There are different temperature scales. One of the most common scales in practice is the Celsius scale. The main points of this scale are the melting temperature of ice and the boiling point of water at normal atmospheric pressure (760 mm Hg). The first point was assigned a value of 0 °C, and the second - 100 °C. The distance between these points was divided into 100 equal parts and received the Celsius scale. The temperature unit on this scale is 1°C. In addition to the Celsius scale, the temperature scale is widely used, called absolute(thermodynamic) temperature scale, or Kelvin scale. For zero on this scale, a temperature of -273 ° C (more precisely -273.15 ° C) is taken. This temperature is called absolute zero temperatures and is denoted by 0 K. The unit of temperature is one kelvin (1 K); it is equal to 1 degree Celsius. Accordingly, the melting temperature of ice on the absolute temperature scale is 273 K (273.15 K), and the boiling point of water is 373 K (373.15 K).
The temperature on the absolute scale is denoted by the letter \ (T \) . The relationship between absolute temperature \((T) \) and Celsius temperature \(((t)^\circ) \) is expressed by the formula:
\[ T=t^\circ+273 \]
Part 1
1. Brownian motion of paint particles in water is a consequence of
1) attraction between atoms and molecules
2) repulsion between atoms and molecules
3) chaotic and continuous motion of molecules
4) displacement of water layers due to the temperature difference between the lower and upper layers
2. In which of the following situations are we talking about Brownian motion?
1) random movement of dust particles in the air
2) the spread of odors
3) oscillatory motion of particles in the nodes of the crystal lattice
4) translational movement of gas molecules
3. What do the words mean: "Molecules move randomly"?
A. There is no preferred direction of movement of molecules.
B. The movement of molecules does not obey any laws.
Correct answer
1) only A
2) only B
3) both A and B
4) neither A nor B
4. The position of the molecular-kinetic theory of the structure of matter that particles of matter participate in continuous chaotic motion refers to
1) only for gases
2) only liquids
3) only for gases and liquids
4) to gases, liquids and solids
5. What (s) position (s) of the molecular-kinetic theory of the structure of matter confirms the phenomenon of diffusion?
A. Molecules are in continuous chaotic motion
B. There are gaps between molecules
Correct answer
1) only A
2) only B
3) both A and B
4) neither A nor B
6. At the same temperature, diffusion in liquids occurs
1) faster than in solids
2) faster than in gases
3) slower than in solids
4) at the same speed as in gases
7. Indicate a pair of substances, the diffusion rate of which is the smallest, all other things being equal
1) a solution of copper sulfate and water
2) ether vapor and air
3) iron and aluminum plates
4) water and alcohol
8. Water boils and turns into steam at 100°C. The average speed of movement of vapor molecules
1) is equal to the average speed of movement of water molecules
2) more than the average speed of movement of water molecules
3) less than the average speed of movement of water molecules
4) depends on atmospheric pressure
9. Thermal motion of molecules
1) stops at 0 °C
2) stops at 100 °C
3) continuously
4) has a certain direction
10. Water is heated from room temperature to 80°C. What happens to the average speed of water molecules?
1) decreases
2) increases
3) does not change
4) first increases, and starting from a certain temperature value, remains unchanged
11. One glass of water is on the table in a warm room, the other is in the refrigerator. The average speed of water molecules in a glass in a refrigerator
1) is equal to the average speed of movement of water molecules in a glass standing on a table
2) more than the average speed of movement of water molecules in a glass standing on a table
3) less than the average speed of movement of water molecules in a glass standing on a table
4) equal to zero
12. From the list of statements below, choose the two correct ones and write their numbers in the table
1) thermal motion of molecules occurs only at a temperature greater than 0 ° C
2) diffusion in solids is impossible
3) attractive and repulsive forces act simultaneously between molecules
4) a molecule is the smallest particle of a substance
5) the diffusion rate increases with increasing temperature
13. A cotton swab soaked in perfume was brought to the physics office, and a vessel into which a solution of copper sulphate (a blue solution) was poured, and water was carefully poured on top (Fig. 1). It was noticed that the smell of perfume spread throughout the volume of the entire cabinet in a few minutes, while the boundary between the two liquids in the vessel disappeared only after two weeks (Fig. 2).
Choose from the proposed list two statements that correspond to the results of the experimental observations. List their numbers.
1) The diffusion process can be observed in gases and liquids.
2) The diffusion rate depends on the temperature of the substance.
3) The diffusion rate depends on the aggregate state of the substance.
4) The diffusion rate depends on the type of liquids.
5) In solids, the diffusion rate is the lowest.
Answers
Back forward
Attention! The slide preview is for informational purposes only and may not represent the full extent of the presentation. If you are interested in this work, please download the full version.
Goals.
- Educational.
- Give the concept of temperature as a measure of average kinetic energy; consider the history of the creation of thermometers, compare various temperature scales; to form the ability to apply the acquired knowledge to solve problems and perform practical tasks, to expand the horizons of students in the field of thermal phenomena.
- Educational.
- Developing the ability to listen to the interlocutor, to express their own point of view
- Developing.
- The development of students' voluntary attention, thinking (the ability to analyze, compare, build analogies, draw conclusions.), Cognitive interest (based on a physical experiment);
- formation of worldview concepts about the cognizability of the world.
DURING THE CLASSES
Hello, have a seat.
When studying mechanics, we were interested in the motion of bodies. Now we will consider the phenomena associated with a change in the properties of bodies at rest. We will study the heating and cooling of air, the melting of ice, the melting of metals, the boiling of water, etc. Such phenomena are called thermal phenomena.
We know that when cold water is heated, it first becomes warm and then hot. The metal part taken out of the flame gradually cools. The air surrounding the hot water heaters becomes hot, etc.
The words "cold", "warm", "hot" denote the thermal state of bodies. The quantity characterizing the thermal state of bodies is temperature.
Everyone knows that the temperature of hot water is higher than the temperature of cold water. In winter, the air temperature outside is lower than in summer.
All molecules of any substance are continuously and randomly (chaotically) moving.
The random random motion of molecules is called thermal motion.
What is the difference between thermal motion and mechanical motion?
It involves many particles with different trajectories. The movement never stops. (Example: Brownian motion)
Demonstration of the Brownian motion model
What does thermal motion depend on?
- Experiment number 1: Let's put a piece of sugar in cold water, and the other in hot. Which will dissolve faster?
- Experiment number 2: Let's put 2 pieces of sugar (one larger than the other) in cold water. Which will dissolve faster?
The question of what temperature is, turned out to be very difficult. What is the difference between hot water and cold water? For a long time there was no clear answer to this question. Today we know that at any temperature, water is made up of the same molecules. Then what exactly changes in water as its temperature increases? We have seen from experience that sugar dissolves much faster in hot water. Dissolution occurs due to diffusion. Thus, diffusion at higher temperatures is faster than at lower temperatures.
But the cause of diffusion is the movement of molecules. This means that there is a relationship between the speed of movement of molecules and the temperature of a body: In a body with a higher temperature, the molecules move faster.
But the temperature depends not only on the average speed of the molecules. So, for example, oxygen, the average speed of the molecules of which is 440 m/s, has a temperature of 20 °C, and nitrogen, with the same average speed of the molecules, has a temperature of 16 °C. The lower temperature of nitrogen is due to the fact that nitrogen molecules are lighter than oxygen molecules. Thus, the temperature of a substance is determined not only by the average velocity of its molecules, but also by their mass. We see the same in experiment No. 2.
We know quantities that depend on both the speed and the mass of the particle. These are momentum and kinetic energy. Scientists have established that it is the kinetic energy of the molecules that determines the temperature of the body: temperature is a measure of the average kinetic energy of the particles of a body; the greater this energy, the higher the temperature of the body.
So, when bodies are heated, the average kinetic energy of molecules increases, and they begin to move faster; when cooled, the energy of the molecules decreases, and they begin to move more slowly.
Temperature is a value that characterizes the thermal state of the body. A measure of the "warmth" of a body. The higher the temperature of a body, the more energy its atoms and molecules have on average.
Can one only rely on one's own sensations to judge the degree of body heat?
- Experience number 1: Touch a wooden object with one hand and a metal object with the other.
Compare sensations
Although both objects are at the same temperature, one hand will feel cold and the other warm
- Experience number 2: take three vessels with hot, warm and cold water. Dip one hand into a vessel of cold water and the other into a vessel of hot water. After a while, both hands are lowered into a vessel with warm water.
Compare sensations
The hand that was in hot water now feels cold, and the hand that was in cold water now feels warm, even though both hands are in the same vessel
We have proven that our feelings are subjective. Instruments are needed to confirm them.
Instruments used to measure temperature are called thermometers. The operation of such a thermometer is based on the thermal expansion of a substance. When heated, the column of the substance used in the thermometer (for example, mercury or alcohol) increases, and when cooled, it decreases. The first liquid thermometer was invented in 1631 by the French physicist J. Rey.
The temperature of the body will change until it comes into thermal equilibrium with the environment.
The law of thermal equilibrium: for any group of isolated bodies, after some time, the temperatures become the same, i.e. a state of thermal equilibrium occurs.
It should be remembered that any thermometer always shows its own temperature. To determine the temperature of the environment, the thermometer should be placed in this environment and wait until the temperature of the device stops changing, taking a value equal to the ambient temperature. When the temperature of the medium changes, the temperature of the thermometer will also change.
A medical thermometer, designed to measure the temperature of a person's body, operates somewhat differently. It belongs to the so-called maximum thermometers, fixing the highest temperature to which they were heated. Having measured your own temperature, you may notice that, being in a colder (compared to the human body) environment, the medical thermometer continues to show the same value. To return the mercury column to its original state, this thermometer must be shaken.
With a laboratory thermometer used to measure the temperature of the medium, this is not necessary.
Thermometers used in everyday life allow you to express the temperature of a substance in degrees Celsius (°C).
A. Celsius (1701-1744) - Swedish scientist who proposed the use of a centigrade temperature scale. In the Celsius temperature scale, zero (from the middle of the 18th century) is the temperature of melting ice, and 100 degrees is the boiling point of water at normal atmospheric pressure.
We will listen to the message about the history of the development of thermometers (Presentation by Sidorova E.)
Liquid thermometers are based on the principle of changing the volume of liquid that is poured into the thermometer (usually alcohol or mercury) as the ambient temperature changes. Disadvantage: different liquids expand differently, so the readings of thermometers differ: Mercury -50 0 С; glycerin -47.6 0 С
We tried to make a liquid thermometer at home. Let's see what came of it. (Video by Brykina V. Appendix 1)
We learned that there are different temperature scales. In addition to the Celsius scale, the Kelvin scale is widely used. The concept of absolute temperature was introduced by W. Thomson (Kelvin). The absolute temperature scale is called the Kelvin scale or the thermodynamic temperature scale.
The unit of absolute temperature is the kelvin (K).
Absolute zero - the lowest possible temperature at which nothing can be colder and it is theoretically impossible to extract thermal energy from a substance, the temperature at which the thermal movement of molecules stops
Absolute zero is defined as 0 K, which is approximately 273.15 °C
One Kelvin is equal to one degree T=t+273
Questions from the exam
Which of the following options for measuring the temperature of hot water with a thermometer gives a more correct result?
1) The thermometer is lowered into the water and, after taking it out of the water after a few minutes, the readings are taken.
2) The thermometer is lowered into the water and wait until the temperature stops changing. After that, without removing the thermometer from the water, take its readings.
3) The thermometer is lowered into the water and, without removing it from the water, immediately take readings
4) The thermometer is lowered into the water, then quickly removed from the water and the readings are taken
The figure shows part of the scale of a thermometer hanging outside the window. The air temperature outside is
- 18 0 С
- 14 0 С
- 21 0 С
- 22 0 С
Solve problems No. 915, 916 (“Collection of problems in physics 7-9” by V.I. Lukashik, E.V. Ivanova)
- Homework: Paragraph 28
- No. 128 D “Collection of problems in physics 7-9” V.I. Lukashik, E.V. Ivanova
Methodological support
- “Physics 8” S.V. Gromov, N.A. motherland
- “Collection of problems in physics 7-9” V.I.Lukashik, E.V. Ivanova
- Drawings that are in the public domain of the Internet
Fundamentals of the molecular-kinetic theory of the structure of matter
The fundamentals of the molecular kinetic theory were developed by M.V. Lomonosov, L. Boltzmann, J. Maxwell and others. This theory is based on the following provisions:
1. All substances consist of the smallest particles - molecules. Molecules in complex substances consist of even smaller particles - atoms. Different combinations of atoms create kinds of molecules. An atom consists of a positively charged nucleus surrounded by a negatively charged electron shell. The mass of molecules and atoms is measured in atomic mass units (amu). The diameter of atoms and molecules is of the order of 10 - 10 cm. The amount of a substance that contains the number of particles (atoms or molecules) equal to the number of atoms in 0.012 kg of carbon isotope C is called we pray.
Molecules collide with each other, changing speed both in magnitude and in direction. In this case, their total kinetic energy is redistributed. A body consisting of molecules is considered as a system of moving and interacting particles. Such a system of molecules has an energy consisting of the potential energy of particle interaction and the kinetic energy of particle motion. This energy is called body's internal energy. The amount of internal energy transferred between bodies during heat exchange is called the amount of heat (joule, cal). Joule - SI. 1 cal = 4.18 J. Atoms and molecules are in continuous motion, which is called thermal. The main property of thermal motion is its continuity (chaoticity). To quantitatively characterize the intensity of thermal motion, the concept of body temperature is introduced. The more intense the thermal movement of molecules in the body, the higher its temperature. When two bodies come into contact, energy passes from a more heated body to a less heated one, and in the end is established state of thermal equilibrium.
From the point of view of molecular kinetic concepts temperature is a quantity that characterizes the average kinetic energy of the translational motion of molecules or atoms. The unit of measure for heat temperature is degree.(One hundredth of the difference between the boiling and freezing points of pure water at atmospheric pressure). The Kelvin absolute temperature scale was introduced into physics. A degree Celsius is equal to a degree Kelvin. At a temperature of -273 C, the translational motion of gas molecules (absolute zero) should stop, i.e. the system (body) has the lowest possible energy.
The main provisions of the molecular-kinetic theory of the structure of matter are confirmed by numerous experiments and phenomena (diffusion, Brownian motion, mixing of liquids, compressibility of various substances, dissolution of solids in liquids, etc.). Modern experimental methods - X-ray diffraction analysis, observations with an electron microscope, and others - have enriched our understanding of the structure of matter. In a gas, there are relatively large distances between molecules, and the forces of attraction are negligible. Gas molecules tend to always be evenly distributed over the entire volume it occupies. The gas exerts pressure on the walls of the vessel in which it is located. This pressure is due to the impacts of moving molecules. When studying the kinetic theory of gas, one considers the so-called ideal gas. A gas in which we neglect the forces of intermolecular interaction and the volume of gas molecules. Assuming that during collisions the molecules of an ideal gas are like absolutely elastic balls.
