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 changes.
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
All molecules of any substance are continuously and randomly (chaotically) moving.
The movement of molecules in different bodies occurs in different ways.
Gas molecules randomly move at high speeds (hundreds of m/s) throughout the entire gas volume. 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, particles oscillate around the equilibrium position.
As the temperature increases, the speed of the particles increases, so the chaotic motion of particles is usually called thermal.
BROWNIAN MOTION
Proof of the thermal motion of molecules.
Brownian motion was discovered by the English botanist Robert Brown (1773-1858).
If the smallest grains of a substance are sprayed on the surface of a liquid,
they will keep moving.
These Brownian particles move under the influence of impacts of liquid molecules. Because Since the thermal motion of molecules is a continuous and random motion, then the speed of movement of Brownian particles will randomly change in magnitude and direction.
Brownian motion is eternal and never stops.
LOOK AT THE BOOKSHELF!
HOME LABORATORY WORK
1. Take three glasses. Pour boiling water into the first, warm water into the second and cold water into the third.
Throw a pinch of granulated tea into each glass. What did you notice?
2. Take an empty plastic bottle, after cooling it, lower the neck into a glass of water and grab the bottle with your palms, but do not press. Watch for a few minutes.
3. On the neck of the same, but again cooled bottle, put an inverted cork soaked in water and also clasp it with warm palms. Watch for a few minutes.
4. Pour water into a shallow dish to a height of 1 - 1.5 cm, put in it a glass turned upside down and preheated with hot water. Watch for a few minutes.
I'm waiting for a report with explanations of what I saw. Who is first?
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.
Instruments used to measure temperature are called thermometers.
The principle of temperature measurement.
The temperature is not directly measured! The measured value depends on the temperature!
In modern liquid thermometers, this is the volume of alcohol or mercury (in Galileo's thermoscope, the volume of gas). 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.
This is the law of thermal equilibrium:
for any group of isolated bodies, after some time, the temperatures become the same,
those. thermal equilibrium occurs
... 
HAVE A HOME EXPERIENCE
Take three basins of water: one with very hot water, another with moderately warm water, and the third with very cold water. Now briefly lower your left hand into a bowl of hot water, and your right hand into cold water. After a couple of minutes, remove your hands from hot and cold water and lower them into a bowl of warm water. Now ask each hand what does it "tell" you about the temperature of the water?
THERMOMETER - DIY
Take a small glass vial (in such vials in pharmacies they sell, for example, brilliant green), a cork (preferably rubber) and a thin transparent tube (you can take an empty transparent rod from a ballpoint pen).
Make a hole in the cork and close the vial. Take a drop of tinted water into the tube and insert the rod into the cork. Seal the gap between the cork and the rod well.
The thermometer is ready.
Now it is necessary to calibrate it, i.e. make a scale.
It is clear that when the air in the bubble is heated, it will expand, and a drop of liquid will rise up the tube. Your task is to mark on the rod or the cardboard attached to it the divisions corresponding to different temperatures.
For graduation, you can take another ready-made thermometer and lower both thermometers into a glass of warm water. Thermometer readings must match. Therefore, if the finished thermometer shows a temperature of, for example, 40 degrees, you can safely mark 40 on the stem of your thermometer in the place where the drop of liquid is located. The water in the glass will cool down, and you will be able to mark the measuring scale in this way.
You can make a thermometer by completely filling it with liquid.
And it is possible in another way:
Make a hole in the cap of a plastic bottle and insert a thin plastic tube.
Partially fill the bottle with water and fix it to the wall. Mark the temperature scale at the free end of the tube. You can calibrate the scale using a conventional room thermometer.
When the temperature in the room changes, the water will expand or contract, and the water level in the tube will also “crawl” along the scale.
And you can see how the thermometer works!
Grab the bottle with your hands and warm it up.
What happened to the water level in the tube?
TEMPERATURE SCALE
Celsius scale - introduced by the Swedish physicist A. Celsius in 1742. Designation: C. There are both positive and negative temperatures on the scale. Reference points: 0C - melting temperature of ice, 100C - boiling point of water.
The Fahrenheit scale was introduced by Fahrenheit, a Dutch glass blower, in 1724. Designation: F. There are both positive and negative temperatures on the scale. Reference points: 32F is the melting temperature of ice, 212F is the boiling point of water.
The Réaumur scale was introduced by the French physicist Réaumur in 1726. Designation: R. There are both positive and negative temperatures on the scale. Reference points: 0R - melting temperature of ice, 80R - boiling point of water.
The Kelvin scale was introduced by the English physicist Thomson (Lord Kelvin) in 1848. Designation: K. There are only positive temperatures on the scale. Reference points: 0K - absolute zero, 273K - ice melting temperature. T = t + 273
THERMOSCOPE
The first device for determining the temperature was invented by Galileo in 1592. A small glass bottle was soldered to a thin tube with an open end.
The balloon was heated by hand and the end of the tube was immersed in a vessel with water. The balloon was cooled to ambient temperature and the water level in the tube rose. Those. by changing the volume of gas in the vessel, it was possible to judge the change in temperature. There was no numerical scale here yet, so such an instrument was called a thermoscope. The measuring scale appeared only after 150 years!
DO YOU KNOW
The highest temperature on Earth recorded in Libya in 1922 is +57.80C;
the lowest temperature recorded on Earth is -89.20C;
above the head of a person, the temperature is higher than the ambient temperature by 1 - 1.50С; average temperature of animals: horses - 380C, sheep - 400C, chickens - 410C,
temperature in the center of the Earth - 200000С;
temperature on the surface of the Sun - 6000 K, in the center - 20 million degrees.
What is the temperature of the Earth's interior?
Previously, various hypothetical assumptions were made and calculations were made, according to which the temperature at a depth of 15 km was 100...400°C. Now the Kola Superdeep Well,
which passed the mark of 12 km, gave an exact answer to the question posed. Initially (up to 3 km), the temperature increased by 1° for every 100 m of penetration, then this increase was 2.5° for every new 100 m. At a depth of 10 km, the temperature of the Earth's interior turned out to be 180°C!
Science and life
By the end of the 18th century, the number of invented temperature scales reached two dozen.
Italian polar explorers, having made an expedition to Antarctica, faced an amazing mystery. Near Ingle Bay, they discovered an ice gorge, where super-fast and super-cold winds constantly blow. A stream of air with a temperature of minus 90 degrees rushes at a speed of 200 km per hour. It is not surprising that this gorge was called the "gates of hell" - no one can be there without risk to life for more than one minute: the wind carries ice particles with such force that it instantly tears clothes to shreds.
Shall we break our heads?
Tricky tasks
1. How to measure the body temperature of an ant with a conventional thermometer?
2. There are thermometers that use water. Why are such water thermometers inconvenient for measuring temperatures close to the freezing point of water?
Waiting for an answer (at the lesson or by mail)!
DO YOU KNOW THAT?
In fact, the Swedish astronomer and physicist Celsius proposed a scale in which the boiling point of water was indicated by the number 0, and the melting point of ice by the number 100! "But in winter there will be no negative numbers!" Celsius liked to say. But then the scale was "turned over".
· A temperature of -40 degrees Celsius is exactly equal to a temperature of -40 degrees Fahrenheit. This is the only temperature at which these two scales converge.
At one time in physical laboratories they used the so-called weight thermometer to measure temperature. It consisted of a hollow platinum ball filled with mercury, which had a capillary hole. The change in temperature was judged by the amount of mercury flowing out of the hole.
It turns out there is a flat thermometer. This is a "piece of paper" that is placed on the patient's forehead. At high temperatures, the "paper" becomes red.
Our senses, usually reliable, can fail in determining the temperature. For example, the experience is known when one hand is dipped in hot water and the other in cold water. If, after some time, both hands are immersed in warm water, then the hand that was previously in hot water will feel cold, and the hand that was in cold water will feel hot!
The concept of temperature is not applicable to a single molecule. One can talk about temperature only if there is a sufficiently large set of particles.
Most often, physicists measure temperature on the Kelvin scale: 0 degrees Celsius = 273 degrees Kelvin!
The highest temperature.
It was obtained in the center of the explosion of a thermonuclear bomb - about 300...400 million °C. The maximum temperature reached in the course of a controlled thermonuclear reaction at the TOKAMAK fusion test facility at the Princeton Plasma Physics Laboratory, USA, in June 1986, is 200 million °C.
The lowest temperature.
Absolute zero on the Kelvin scale (0 K) corresponds to -273.15° Celsius or -459.67° Fahrenheit. The lowest temperature, 2 10–9 K (two-billionth of a degree) above absolute zero, was achieved in a two-stage nuclear demagnetization cryostat at the Low Temperature Laboratory of the Helsinki University of Technology, Finland, by a group of scientists led by Professor Olli Lounasmaa (b. 1930. ), which was announced in October 1989.
The smallest thermometer ever.
Dr. Frederick Sacks, a biophysicist at the State University of New York, Buffalo, USA, has designed a microthermometer to measure the temperature of individual living cells. The diameter of the thermometer tip is 1 micron, i.e. 1/50 of the diameter of a human hair.
