Theory: Atoms and molecules are in continuous thermal motion, move randomly, constantly change direction and velocity modulus due to collisions.
The higher the temperature, the higher the speed of the molecules. As the temperature decreases, the speed of the molecules decreases. There is a temperature, which is called "absolute zero" - the temperature (-273 ° C) at which the thermal movement of molecules stops. But "absolute zero" is unattainable.
Brownian motion is the random movement of microscopic particles of solid matter visible suspended in a liquid or gas, caused by the thermal motion of particles of a liquid or gas. This phenomenon was first observed in 1827 by Robert Brown. He studied the pollen of plants, which was in the aquatic environment. Brown noticed that pollen shifts all the time over time, and the higher the temperature, the faster the rate of pollen shift. He suggested that the movement of pollen is due to the fact that water molecules hit the pollen and make it move. 
Diffusion is the process of mutual penetration of molecules of one substance into the gaps between the molecules of another substance. 
An example of Brownian motion is
1) random movement of pollen in a drop of water
2) random movement of midges under the lantern
3) dissolution of solids in liquids
4) the penetration of nutrients from the soil into the roots of plants
Decision: from the definition of Brownian motion, it is clear that the correct answer is 1. Pollen moves randomly due to the fact that water molecules hit it. The erratic movement of midges under the lamp is not suitable, since the midges themselves choose the direction of movement, the last two answers are examples of diffusion.
Answer: 1.
Oge assignment in physics (I will solve the exam): Which of the following statements is(are) correct?
A. Molecules or atoms in a substance are in continuous thermal motion, and one of the arguments in favor of this is the phenomenon of diffusion.
B. Molecules or atoms in matter are in continuous thermal motion, and the proof of this is the phenomenon of convection.
1) only A
2) only B
3) both A and B
4) neither A nor B
Decision: Diffusion is the process of mutual penetration of molecules of one substance into the gaps between the molecules of another substance. The first statement is true, the Convention is the transfer of internal energy with layers of liquid or gas, it turns out that the second statement is not true.
Answer: 1.
Oge assignment in physics (fipi): 2) A lead ball is heated in a candle flame. How does the volume of the ball and the average speed of movement of its molecules change during the heating process?
Establish a correspondence between physical quantities and their possible changes.
For each value, determine the appropriate nature of the change:
1) increases
2) decreases
3) does not change
Write in the table the selected numbers for each physical quantity. Numbers in the answer may be repeated.
Solution (Thanks to Milena) : 2) 1. The volume of the ball will increase due to the fact that the molecules will start moving faster.
2. The speed of molecules when heated will increase.
Answer: 11.
The task of the demo version of the OGE 2019: One of the provisions of the molecular-kinetic theory of the structure of matter is that "particles of matter (molecules, atoms, ions) are in continuous chaotic motion." What do the words "continuous movement" mean?
1) Particles always move in a certain direction.
2) The movement of particles of matter does not obey any laws.
3) The particles all move together in one direction or the other.
4) The movement of molecules never stops.
Decision: Molecules are moving, due to collisions, the speed of the molecules is constantly changing, so we cannot calculate the speed and direction of each molecule, but we can calculate the root mean square speed of the molecules, and it is related to temperature, as the temperature decreases, the speed of the molecules decreases. It is calculated that the temperature at which the movement of molecules will stop is -273 °C (the lowest possible temperature in nature). But it is not achievable. so the molecules never stop moving.
The events of the physical world are inextricably linked with changes in temperature. Every person gets acquainted with it in early childhood, when he realizes that ice is cold, and boiling water burns. At the same time, the understanding comes that the processes of temperature change do not occur instantly. Later, at school, the student learns that this is connected with thermal motion. And a whole section of physics is allocated to the processes associated with temperature.
What is temperature?
This scientific concept was introduced to replace ordinary terms. In everyday life, words such as hot, cold or warm constantly appear. All of them speak about the degree of heating of the body. This is how it is defined in physics, only with the addition that it is a scalar quantity. After all, temperature has no direction, but only a numerical value.
In the International System of Units (SI), temperature is measured in degrees Celsius (ºC). But in many formulas describing thermal phenomena, it is required to convert it to Kelvin (K). There is a simple formula for this: T \u003d t + 273. In it, T is the temperature in Kelvin, and t is in Celsius. The concept of absolute zero temperature is associated with the Kelvin scale.
There are several other temperature scales. In Europe and America, for example, Fahrenheit (F) is used. Therefore, they must be able to write in Celsius. To do this, subtract 32 from the readings in F, then divide it by 1.8.
home experiment
In its explanation, it is required to know such concepts as temperature, thermal motion. And yes, this experiment is easy to do.
It will require three containers. They should be large enough so that the hands can easily fit in them. Fill them with water of different temperatures. In the first, it must be very cold. In the second - heated. In the third, pour hot water, one in which it will be possible to hold a hand.
Now the experience itself. Dip your left hand in a container of cold water, right - with the hottest. Wait a couple of minutes. Take them out and immediately immerse them in a container of warm water.
The result will be unexpected. The left hand will feel that the water is warm, while the right hand will feel cold water. This is due to the fact that thermal equilibrium is first established with those liquids in which the hands are immersed initially. And then this balance is sharply disturbed.
Basic Provisions of Molecular Kinetic Theory
It describes all thermal phenomena. And these statements are quite simple. Therefore, in a conversation about thermal motion, these provisions must be known.
First: substances are formed by the smallest particles located at some distance from each other. Moreover, these particles can be both molecules and atoms. And the distance between them is many times greater than the size of the particles.
Second: in all substances there is a thermal movement of molecules, which never stops. In this case, the particles move randomly (chaotically).
Third: particles interact with each other. This action is due to the forces of attraction and repulsion. Their value depends on the distance between the particles.
Confirmation of the first position of the ICB
The proof that bodies are composed of particles between which there are gaps is their size. Thus, when a body is heated, its size increases. This happens due to the removal of particles from each other.
Another confirmation of the above is diffusion. That is, the penetration of molecules of one substance between the particles of another. Moreover, this movement is mutual. Diffusion proceeds the faster, the farther apart the molecules are located. Therefore, in gases, mutual penetration will occur much faster than in liquids. And in solids, diffusion takes years.
By the way, the latter process also explains thermal motion. After all, the mutual penetration of substances into each other occurs without any interference from the outside. But it can be accelerated by heating the body.
Confirmation of the second position of the ICB
A striking proof that there is thermal motion is the Brownian motion of particles. It is considered for suspended particles, that is, for those that are significantly larger than the molecules of a substance. These particles can be dust particles or grains. And they are supposed to be placed in water or gas.
The reason for the random movement of a suspended particle is that molecules act on it from all sides. Their action is erratic. The magnitude of the impacts at each point in time is different. Therefore, the resulting force is directed in one direction or the other.
If we talk about the speed of thermal motion of molecules, then there is a special name for it - root mean square. It can be calculated using the formula:
v = √[(3kT)/m0].
In it, T is the temperature in Kelvin, m 0 is the mass of one molecule, k is the Boltzmann constant (k \u003d 1.38 * 10 -23 J / K).
Confirmation of the third provision of the ICB
Particles attract and repel. In explaining many processes associated with thermal motion, this knowledge turns out to be important.
After all, the forces of interaction depend on the state of aggregation of the substance. So, gases practically do not have them, since the particles are removed so far that their effect is not manifested. In liquids and solids, they are perceptible and ensure the conservation of the volume of the substance. In the latter, they also guarantee the maintenance of shape.
The proof of the existence of attractive and repulsive forces is the appearance of elastic forces during the deformation of bodies. So, with elongation, the forces of attraction between molecules increase, and with compression, repulsion forces increase. But in both cases, they return the body to its original shape.
Average energy of thermal motion
(pV)/N = (2E)/3.
In this formula, p is pressure, V is volume, N is the number of molecules, and E is the average kinetic energy.
On the other hand, this equation can be written as:
If we combine them, we get the following equality:
It follows from this formula for the average kinetic energy of molecules:
This shows that the energy is proportional to the temperature of the substance. That is, when the latter increases, the particles move faster. This is the essence of thermal motion, which exists as long as there is a temperature other than absolute zero.
thermal motion
Any substance consists of the smallest particles - molecules. Molecule is the smallest particle of a given substance that retains all of its chemical properties. Molecules are located discretely in space, i.e., at certain distances from each other, and are in a state of continuous erratic (chaotic) movement .
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 is 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).
It is impossible to single out any particular direction in which all molecules move. The movement of molecules never stops. We can say that it is continuous. Such a continuous chaotic movement of atoms and molecules is called -. This name is determined by the fact that the speed of movement of molecules depends on the temperature of the body. The greater the average speed of movement of the body's molecules, the higher its temperature. Conversely, the higher the temperature of the body, the greater the average speed of the molecules.
The movement of liquid molecules was discovered by observing Brownian motion - the movement of very small solid particles suspended in it. Each particle continuously makes jumps in arbitrary directions, describing the trajectory in the form of a broken line. This behavior of particles can be explained by assuming that they experience impacts of liquid molecules simultaneously from different sides. The difference in the number of these impacts from opposite directions leads to the motion of the particle, since its mass is commensurate with the masses of the molecules themselves. The movement of such particles was first discovered in 1827 by the English botanist Brown, observing pollen particles in water under a microscope, which is why it was called - Brownian motion.
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 pharmacies they sell, for example, brilliant green in such vials), 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.
