Report
on the topic of:
"Thermal phenomena in nature
and in human life"
Performed
student of 8th grade "A"
Karibova A.V.
Armavir, 2010
Phenomena occur around us that are outwardly very indirectly related to mechanical movement. These are phenomena observed when the temperature of bodies changes or when they transition from one state (for example, liquid) to another (solid or gaseous). Such phenomena are called thermal. Thermal phenomena play a huge role in the lives of people, animals and plants. A change in temperature of 20-30° C when the season changes changes everything around us. The possibility of life on Earth depends on the ambient temperature. People achieved relative independence from the environment after they learned to make and maintain fire. This was one of the greatest discoveries made at the dawn of human development.
The history of the development of ideas about the nature of thermal phenomena is an example of the complex and contradictory way in which scientific truth is comprehended.
Many ancient philosophers considered fire and the heat associated with it as one of the elements, which, along with earth, water and air, forms all bodies. At the same time, attempts were made to connect heat with movement, since it was noticed that when bodies collide or rub against each other, they heat up.
The first successes towards constructing a scientific theory of heat date back to the beginning of the 17th century, when the thermometer was invented, and it became possible to quantitatively study thermal processes and the properties of macrosystems.
The question of what heat is was again raised. Two opposing points of view have emerged. According to one of them, the material theory of heat, heat was considered as a special kind of weightless “liquid” capable of flowing from one body to another. This liquid was called caloric. The more caloric in the body, the higher the body temperature.
According to another point of view, heat is a type of internal movement of body particles. The faster the particles of a body move, the higher its temperature.
Thus, the idea of thermal phenomena and properties was associated with the atomistic teaching of ancient philosophers about the structure of matter. Within the framework of such ideas, the theory of heat was originally called corpuscular, from the word “corpuscle” (particle). Scientists adhered to it: Newton, Hooke, Boyle, Bernoulli.
A great contribution to the development of the corpuscular theory of heat was made by the great Russian scientist M.V. Lomonosov. He viewed heat as the rotational movement of particles of matter. With the help of his theory, he explained in general the processes of melting, evaporation and thermal conductivity, and also came to the conclusion that there is a “greatest or last degree of cold” when the movement of particles of matter stops. Thanks to the work of Lomonosov, there were very few supporters of the real theory of heat among Russian scientists.
But still, despite the many advantages of the corpuscular theory of heat, by the middle of the 18th century. The caloric theory won a temporary victory. This happened after the conservation of heat during heat transfer was experimentally proven. Hence the conclusion was made about the conservation (non-destruction) of thermal fluid - caloric. In the material theory, the concept of heat capacity of bodies was introduced and a quantitative theory of thermal conductivity was constructed. Many terms introduced at that time have survived to this day.
In the middle of the 19th century. the connection between mechanical work and the amount of heat was proven. Like work, the amount of heat turned out to be a measure of the change in energy. Heating of a body is not associated with an increase in the amount of a special weightless “liquid” in it, but with an increase in its energy. The caloric principle was replaced by the much more profound law of conservation of energy. Heat was found to be a form of energy.
Significant contributions to the development of theories of thermal phenomena and properties of macrosystems were made by the German physicist R. Clausius (1822-1888), the English theoretical physicist J. Maxwell, the Austrian physicist L. Boltzmann (1844-1906) and other scientists.
It so happens that the nature of thermal phenomena is explained in physics in two ways: the thermodynamic approach and the molecular-kinetic theory of matter.
The thermodynamic approach considers heat from the perspective of macroscopic properties of matter (pressure, temperature, volume, density, etc.).
The molecular kinetic theory connects the occurrence of thermal phenomena and processes with the peculiarities of the internal structure of matter and studies the reasons that determine thermal movement.
So, let's consider thermal phenomena in human life.
Heating and cooling, evaporation and boiling, melting and solidification, condensation are all examples of thermal phenomena.
The main source of heat on Earth is the Sun. But, in addition, people use many artificial heat sources: fires, stoves, water heating, gas and electric heaters, etc.
You know that if you put a cold spoon into hot tea, after a while it will heat up. In this case, the tea will give up some of its heat not only to the spoon, but also to the surrounding air. From the example it is clear that heat can be transferred from a body that is more heated to a body that is less heated. There are three ways of transferring heat − thermal conductivity, convection, radiation.
Heating a spoon in hot tea - example thermal conductivity. All metals have good thermal conductivity.
Convection Heat is transferred in liquids and gases. When we heat water in a saucepan or kettle, the lower layers of water warm up first, they become lighter and rush upward, giving way to cold water. Convection occurs in a room when the heating is on. Hot air from the battery rises and cold air falls.
But neither thermal conductivity nor convection can explain how, for example, the Sun, far from us, heats the Earth. In this case, heat is transferred through airless space radiation(heat rays).
A thermometer is used to measure temperature. In everyday life, they use room or medical thermometers.
When we talk about Celsius temperature, we mean a temperature scale in which 0°C corresponds to the freezing point of water, and 100°C is its boiling point.
In some countries (USA, UK) the Fahrenheit scale is used. In it, 212°F corresponds to 100°C. Converting temperature from one scale to another is not very simple, but if necessary, each of you can do it yourself. To convert a Celsius temperature to a Fahrenheit temperature, multiply the Celsius temperature by 9, divide by 5, and add 32. To do the reverse conversion, subtract 32 from the Fahrenheit temperature, multiply the remainder by 5, and divide by 9.
In physics and astrophysics, another scale is often used - the Kelvin scale. In it, the lowest temperature in nature (absolute zero) is taken as 0. It corresponds to −273°C. The unit of measurement in this scale is Kelvin (K). To convert temperature in Celsius to temperature in Kelvin, you need to add 273 to degrees Celsius. For example, in Celsius 100°, and in Kelvin 373 K. To convert back, you need to subtract 273. For example, 0 K is −273°C.
It is useful to know that the temperature on the surface of the Sun is 6000 K, and inside it is 15,000,000 K. The temperature in outer space far from stars is close to absolute zero.
In nature, we witness thermal phenomena, but sometimes we do not pay attention to their essence. For example, it rains in summer and snows in winter. Dew forms on the leaves. Fog appears.
Knowledge of thermal phenomena helps people design home heaters, heat engines (internal combustion engines, steam turbines, jet engines, etc.), predict the weather, melt metal, create thermal insulation and heat-resistant materials that are used everywhere - from building houses to spaceships.
The text of the work is posted without images and formulas.
The full version of the work is available in the "Work Files" tab in PDF format
Hypothesis: Thanks to scientific knowledge and achievements, lightweight, durable, low-thermal conductivity materials have been created for clothing and home protection, air conditioners, fans and other devices. This allows us to overcome difficulties and many problems associated with heat. But it is still necessary to study thermal phenomena, since they have an extremely large impact on our lives.
Target: study of thermal phenomena and thermal processes.
Tasks: talk about thermal phenomena and thermal processes;
study the theory of thermal phenomena;
in practice, consider the existence of thermal processes;
show the manifestation of these experiences.
Expected Result: conducting experiments and studying the most common thermal processes.
: material on the topic was selected and systematized, experiments and a blitz survey of students were conducted, a presentation was prepared, a poem of one’s own composition was presented.
Thermal phenomena are physical phenomena that are associated with heating and cooling of bodies.
Heating and cooling, evaporation and boiling, melting and solidification, condensation are all examples of thermal phenomena.
Thermal movement - process of chaotic (disorderly) movement
particles that form matter.
The higher the temperature, the greater the speed of particle movement. The thermal motion of atoms and molecules is most often considered. Molecules or atoms of a substance are always in constant random motion.
This movement determines the presence in any substance of internal kinetic energy, which is associated with the temperature of the substance.
Therefore, the random motion in which molecules or atoms are always found is called thermal.
The study of thermal phenomena shows that as much as the mechanical energy of bodies decreases in them, their mechanical and internal energies increase, which remains unchanged during any process.
This is the law of conservation of energy.
Energy does not appear from nothing and does not disappear anywhere.
It can only pass from one type to another, maintaining its full meaning.
The thermal movement of molecules never stops. Therefore, any body always has some kind of internal energy. Internal energy depends on body temperature, the state of aggregation of matter and other factors and does not depend on the mechanical position of the body and its mechanical movement. A change in the internal energy of a body without doing work is called heat transfer .
Heat transfer always occurs in the direction from a body with a higher temperature to a body with a lower temperature.
There are three types of heat transfer:
Thermal processes are a type of thermal phenomena; processes in which the temperature of bodies and substances changes, and it is also possible to change them states of aggregation. Thermal processes include:
Heating
Cooling
Vaporization
Boiling
Evaporation
Crystallization
Melting
Condensation
Combustion
Sublimation
Desublimation
Let us consider, as an example, a substance that can be in three states of aggregation: water (L - liquid, T - solid, G - gaseous)
Heating- the process of increasing the temperature of a body or substance. Heating is accompanied by the absorption of heat from the environment. When heated, the state of aggregation of a substance does not change.
Experiment 1: Heating.
Let's take water from the tap into a glass and measure its temperature (25°C),
then put the glass in a warm place (window on the sunny side), and after a while measure the water temperature (30°C).
After waiting some more time, I measured the temperature again (35°C). Conclusion: The thermometer shows an increase in temperature first by 5°C, and then by 10°C.
Cooling- the process of lowering the temperature of a substance or body; Cooling is accompanied by the release of heat into the environment. When cooled, the state of aggregation of a substance does not change.
Experiment 2: Cooling. Let's see how cooling occurs experimentally.
Let's take hot water from a tap into a glass and measure its temperature (60°C), then place this glass on the windowsill for a while, after which we measure the temperature of the water and it becomes equal (20°C).
Conclusion: the water cools and the thermometer shows a decrease in temperature.
Experiment 3: Boiling.
We encounter boiling water every day at home.
Pour water into the kettle and place it on the stove. First, the water heats up, and then the water boils. This is evidenced by the steam coming out of the kettle's spout.
Conclusion: When the water boils, steam from the neck of the kettle comes out through a small hole and whistles, and we turn off the stove.
Evaporation- This is vaporization occurring from the free surface of a liquid.
Evaporation depends on:
Substance temperatures(the higher the temperature, the more intense the evaporation);
Liquid surface area(the larger the area, the greater the evaporation);
Kind of substance(different substances evaporate at different rates);
Presence of wind(in the presence of wind, evaporation occurs faster).
Experiment 4: Evaporation.
If you have ever observed puddles after rain, then you have undoubtedly noticed that the puddles become smaller and smaller. What happened to the water?
Conclusion: she evaporated!
Crystallization(solidification) is the transition of a substance from a liquid state of aggregation to a solid state. Crystallization is accompanied by the release of energy (heat) into the environment.
Experiment 5: Crystallization. To detect crystallization, let's conduct an experiment.
Let's take water from the tap into a glass and put it in the freezer of the refrigerator. After some time, the substance hardens, i.e. a crust appears on the surface of the water. Then all the water in the glass completely turned into ice, that is, it crystallized.
Conclusion: First the water cools to 0 degrees, then freezes.
Melting- the transition of a substance from a solid to a liquid state. This process is accompanied by the absorption of heat from the environment. To melt a solid crystalline body, a certain amount of heat must be transferred to it.
Experiment 6: Melting. Melting is easily detected experimentally.
We take out a glass of frozen water from the freezer compartment of the refrigerator, which we placed. After some time, water appeared in the glass - the ice began to melt. After some time, all the ice melted, that is, it completely turned from solid to liquid.
Conclusion: Over time, ice receives heat from the environment and will melt over time.
Condensation-transition of a substance from a gaseous state to a liquid state.
Condensation is accompanied by the release of heat into the environment.
Experiment 7: Condensation.
We boiled water and held a cold mirror to the spout of the kettle. After a few minutes, drops of condensed water vapor are clearly visible on the mirror.
Conclusion: steam settling on the mirror turns into water.
The phenomenon of condensation can be observed in summer, in the early cool mornings.
Droplets of water on grass and flowers - dew - indicate that the water vapor contained in the air has condensed.
Combustion is the process of burning fuel, accompanied by the release of energy.
This energy is used in various
spheres of our life.
Experiment 8: Combustion. Every day we can watch natural gas burn in a stove burner. This is the process of fuel combustion.
Also the process of fuel combustion is the process of burning wood. Therefore, to conduct an experiment on fuel combustion, it is enough to just light the gas
burner or match.
Conclusion: When fuel burns, heat is released and a specific smell may appear.
The result of the project: in my project work I studied the most common thermal processes: heating, cooling, vaporization, boiling, evaporation, melting, crystallization, condensation, combustion, sublimation and desublimation.
In addition, the work touched upon such topics as thermal motion, aggregate states of substances, as well as the general theory of thermal phenomena and thermal processes.
Based on simple experiments, one or another thermal phenomenon was considered. The experiments are accompanied by demonstration pictures.
Based on experiments, the following is considered:
The existence of various thermal processes;
The relevance of thermal processes in human life has been proven.
I also conducted a blitz survey of 15 students in grade 9 “A”.
Blitz - survey of 9th grade students.
Questions:
1. What are thermal phenomena?
2. Give examples of thermal phenomena
3. What movement is called thermal?
4. What is thermal conductivity?
5. Aggregate transformations are...
6. The phenomenon of turning liquid into vapor?
7. The phenomenon of turning steam into liquid?
8. What process is called melting?
9. What is evaporation?
10. Name the processes reverse to heating, melting, evaporation?
Answers:
1. Thermal phenomena - physical phenomena associated with heating and cooling of bodies
2. Examples of thermal phenomena: heating and cooling, evaporation and boiling, melting and solidification, condensation
3. Thermal motion - random, chaotic movement of molecules
4. Thermal conduction - transfer of heat from one part to another
5. Aggregate transformations are phenomena of the transition of a substance from one state of aggregation to another
6. Vaporization
7. Condensation
8. Melting is the transition of a substance from a solid to a liquid state. This process is accompanied by the absorption of heat from the environment
9. Evaporation is vaporization occurring from the free surface of a liquid
10. Processes reverse to heating, melting, evaporation - cooling, crystallization, condensation
Blitz survey results:
1. Correct answer - 7 people - 47%
Wrong answer - 8 people - 53%
2. Correct answer -6 people - 40%
Wrong answer -9 people - 60%
3. Correct answer - 10 people - 67%
4. Correct answer -6 people - 40%
Wrong answer - 9 people - 60%
5. Correct answer - 8 people - 53%
6. Correct answer - 12 people - 80%
Wrong answer - 3 people - 20%
7. Correct answer - 8 people - 53%
Wrong answer - 7 people - 47%
8. Correct answer - 10 people - 67%
Wrong answer - 5 people - 33%
9. Correct answer - 13 people - 87%
Wrong answer - 2 people - 13%
10. Correct answer - 8 people -53%
Wrong answer - 7 people - 47%
The flash survey showed that students do not have sufficient knowledge of this topic, and I hope that my project will help them fill the missing gaps on this topic.
The goal and objectives of the project work that I set were completed.
I want to finish my work with a poem that I wrote together with my grandfather.
Thermal phenomena
We study phenomena
We want to know about warmth.
We live in a wonderful world -
Everything is like two and two are four.
We do the work
Having rocked the company of molecules,
We chop a log for firewood -
We feel warm.
A very important task -
This is heat transfer.
Heat can be transferred
Take from heated water.
All bodies are thermally conductive:
The water heats the radiator,
Air flows from bottom to top
Transfers heat into the house.
And the window glass
Keeps the house warm.
There is an air layer in the frame -
It's a mountain for warmth.
It doesn't allow heat to pass through
And he keeps it in the apartment.
Well, during the day, we know ourselves,
The sun will give warmth with its rays...
To know all these properties,
To live in friendship with warmth in the world,
And actually apply -
We need to learn PHYSICS!!!
Bibliography
1. Rakhimbaev M.M. Flash textbook: “Physics. 8th grade". 2. Teaching physics that develops the student. Book 1. Approaches, components, lessons, tasks / Compiled and ed. EM. Braverman: - M.: Association of Physics Teachers, 2003. - 400 p. 3. Dubovitskaya T.D. Diagnosis of the significance of an academic subject for the development of students’ personality. Bulletin of OSU, No. 2, 2004. 4. Kolechenko A.K. Encyclopedia of educational technologies: A manual for teachers. - St. Petersburg: KARO, 2004. 5. Selevko G.K. Pedagogical technologies based on activation, intensification and effective management of educational programs. M.: Research Institute of School Technologies, 2005. 6. Electronic resources: Website http://school-collection.edu.ru Website http://obvad.ucoz.ru/index/0 Website http://zabalkin.narod.ru Website http://somit.ru
Report
on the topic of:
"Thermal phenomena in nature
and in human life"
Performed
student of 8th grade "A"
Karibova A.V.
Armavir, 2010
Phenomena occur around us that are outwardly very indirectly related to mechanical movement. These are phenomena observed when the temperature of bodies changes or when they transition from one state (for example, liquid) to another (solid or gaseous). Such phenomena are called thermal. Thermal phenomena play a huge role in the lives of people, animals and plants. A temperature change of 20-30°C with the change of season changes everything around us. The possibility of life on Earth depends on the ambient temperature. People achieved relative independence from the environment after they learned to make and maintain fire. This was one of the greatest discoveries made at the dawn of human development.
The history of the development of ideas about the nature of thermal phenomena is an example of the complex and contradictory way in which scientific truth is comprehended.
Many ancient philosophers considered fire and the heat associated with it as one of the elements, which, along with earth, water and air, forms all bodies. At the same time, attempts were made to connect heat with movement, since it was noticed that when bodies collide or rub against each other, they heat up.
The first successes towards constructing a scientific theory of heat date back to the beginning of the 17th century, when the thermometer was invented, and it became possible to quantitatively study thermal processes and the properties of macrosystems.
The question of what heat is was again raised. Two opposing points of view have emerged. According to one of them, the material theory of heat, heat was considered as a special kind of weightless “liquid” capable of flowing from one body to another. This liquid was called caloric. The more caloric in the body, the higher the body temperature.
According to another point of view, heat is a type of internal movement of body particles. The faster the particles of a body move, the higher its temperature.
Thus, the idea of thermal phenomena and properties was associated with the atomistic teaching of ancient philosophers about the structure of matter. Within the framework of such ideas, the theory of heat was initially called corpuscular, from the word “corpuscle” (particle). Scientists adhered to it: Newton, Hooke, Boyle, Bernoulli.
A great contribution to the development of the corpuscular theory of heat was made by the great Russian scientist M.V. Lomonosov. He viewed heat as the rotational movement of particles of matter. Using his theory, he explained in general the processes of melting, evaporation and thermal conductivity, and also came to the conclusion that there is a “greatest or last degree of cold” when the movement of particles of matter stops. Thanks to the work of Lomonosov, there were very few supporters of the real theory of heat among Russian scientists.
But still, despite the many advantages of the corpuscular theory of heat, by the middle of the 18th century. The caloric theory won a temporary victory. This happened after the conservation of heat during heat transfer was experimentally proven. Hence the conclusion was made about the conservation (non-destruction) of thermal fluid - caloric. In the material theory, the concept of heat capacity of bodies was introduced and a quantitative theory of thermal conductivity was constructed. Many terms introduced at that time have survived to this day.
In the middle of the 19th century. the connection between mechanical work and the amount of heat was proven. Like work, the amount of heat turned out to be a measure of the change in energy. Heating of a body is not associated with an increase in the amount of a special weightless “liquid” in it, but with an increase in its energy. The caloric principle was replaced by the much more profound law of conservation of energy. Heat was found to be a form of energy.
Significant contributions to the development of theories of thermal phenomena and properties of macrosystems were made by the German physicist R. Clausius (1822-1888), the English theoretical physicist J. Maxwell, the Austrian physicist L. Boltzmann (1844-1906) and other scientists.
It so happens that the nature of thermal phenomena is explained in physics in two ways: the thermodynamic approach and the molecular-kinetic theory of matter.
The thermodynamic approach considers heat from the perspective of macroscopic properties of matter (pressure, temperature, volume, density, etc.).
The molecular kinetic theory connects the occurrence of thermal phenomena and processes with the peculiarities of the internal structure of matter and studies the reasons that determine thermal movement.
So, let's consider thermal phenomena in human life.
Heating and cooling, evaporation and boiling, melting and solidification, condensation are all examples of thermal phenomena.
The main source of heat on Earth is the Sun. But, in addition, people use many artificial heat sources: fires, stoves, water heating, gas and electric heaters, etc.
You know that if you put a cold spoon into hot tea, after a while it will heat up. In this case, the tea will give up some of its heat not only to the spoon, but also to the surrounding air. From the example it is clear that heat can be transferred from a body that is more heated to a body that is less heated. There are three ways to transfer heat - thermal conductivity, convection, radiation.
Heating a spoon in hot tea - example thermal conductivity. All metals have good thermal conductivity.
Convection Heat is transferred in liquids and gases. When we heat water in a saucepan or kettle, the lower layers of water warm up first, they become lighter and rush upward, giving way to cold water. Convection occurs in a room when the heating is on. Hot air from the battery rises and cold air falls.
But neither thermal conductivity nor convection can explain how, for example, the Sun, far from us, heats the Earth. In this case, heat is transferred through airless space radiation(heat rays).
A thermometer is used to measure temperature. In everyday life, they use room or medical thermometers.
When we talk about Celsius temperature, we mean a temperature scale in which 0°C corresponds to the freezing point of water, and 100°C is its boiling point.
In some countries (USA, UK) the Fahrenheit scale is used. In it, 212°F corresponds to 100°C. Converting temperature from one scale to another is not very simple, but if necessary, each of you can do it yourself. To convert a Celsius temperature to a Fahrenheit temperature, multiply the Celsius temperature by 9, divide by 5, and add 32. To do the reverse conversion, subtract 32 from the Fahrenheit temperature, multiply the remainder by 5, and divide by 9.
In physics and astrophysics, another scale is often used - the Kelvin scale. In it, the lowest temperature in nature (absolute zero) is taken as 0. It corresponds to −273°C. The unit of measurement in this scale is Kelvin (K). To convert temperature in Celsius to temperature in Kelvin, you need to add 273 to degrees Celsius. For example, in Celsius 100°, and in Kelvin 373 K. To convert back, you need to subtract 273. For example, 0 K is −273°C.
It is useful to know that the temperature on the surface of the Sun is 6000 K, and inside it is 15,000,000 K. The temperature in outer space far from stars is close to absolute zero.
In nature, we witness thermal phenomena, but sometimes we do not pay attention to their essence. For example, it rains in summer and snows in winter. Dew forms on the leaves. Fog appears.
Knowledge of thermal phenomena helps people design home heaters, heat engines (internal combustion engines, steam turbines, jet engines, etc.), predict the weather, melt metal, create thermal insulation and heat-resistant materials that are used everywhere - from building houses to spaceships.
For the Earth - the Sun. Solar energy underlies many phenomena occurring on the surface and in the atmosphere of the planet. Heating, cooling, evaporation, boiling, condensation are some examples of the types of thermal phenomena that occur around us.
No processes occur by themselves. Each of them has its own source and implementation mechanism. Any thermal phenomena in nature are caused by receiving heat from external sources. Not only the Sun can act as such a source - fire also successfully copes with this role.
To further understand what thermal phenomena are, it is necessary to define heat. Heat is an energy characteristic of heat exchange, in other words, how much energy a body or system gives (receives) during interaction. It can be quantitatively characterized by temperature: the higher it is, the more heat (energy) a given body has.
In the process with each other, heat is transferred from a hot to a cold body, that is, from a body with higher energy to a body with lower energy. This process is called heat transfer. As an example, consider boiling water poured into a glass. After some time, the glass will become hot, i.e., the process of heat transfer from hot water to the cold glass has occurred.
However, thermal phenomena are characterized not only by heat transfer, but also by such a concept as thermal conductivity. What it means can be explained with an example. If you put a frying pan on the fire, its handle, although not in contact with the fire, will heat up just like the rest of the frying pan. Such heating is provided by thermal conductivity. Heating is carried out in one place, and then the whole body is heated. Or it doesn’t heat up - it depends on what thermal conductivity it has. If the thermal conductivity of the body is high, then heat is easily transferred from one area to another, but if the thermal conductivity is low, then heat transfer does not occur.
Before the concept of heat appeared, physics explained thermal phenomena using the concept of “caloric.” It was believed that every substance has a certain substance, similar to a liquid, that performs a task that, in the modern concept, is solved by heat. But the idea of caloric was abandoned after the concept of heat was formulated.
Now we can consider in more detail the practical application of the previously introduced definitions. Thus, thermal conductivity ensures heat exchange between bodies and within the material itself. High thermal conductivity values are characteristic of metals. This is good for dishes and a kettle, because it allows heat to be supplied to the food being prepared. However, materials with low thermal conductivity also find their use. They act as thermal insulators, preventing heat loss - for example, during construction. Thanks to the use of materials with low thermal conductivity, comfortable living conditions in homes are ensured.
However, heat transfer is not limited to the above methods. There is also the possibility of heat transfer without direct contact of bodies. As an example, warm air flows from a heater or radiator of the heating system in an apartment. A stream of warm air emanates from the heated object, heating the room. This method of heat exchange is called convection. In this case, heat transfer is carried out by liquid or gas flows.
If we remember that thermal phenomena occurring on Earth are associated with radiation from the Sun, then another method of heat transfer appears - thermal radiation. It is caused by electromagnetic radiation from a heated body. This is how the Sun heats the Earth.
This material examines various thermal phenomena, describes the source of their occurrence and the mechanisms by which they occur. The issues of practical use of thermal phenomena in everyday practice are considered.
Internal energy and ways of changing it Internal energy is the energy of movement and interaction of the particles that make up the body. Methods of changing internal energy, doing work, heat transfer over a body, the body itself, thermal conductivity, convection, radiation, E increases, E decreases
Heat transfer Heat conduction is a type of heat exchange in which internal energy is transferred from particles of a more heated part of the body to particles of a less heated part of the body (or from a more heated body to a less heated body). Convection is the transfer of energy by flows (or jets) of matter. Radiation is the transfer of energy using various invisible rays emitted by a heated body.
Quantity of heat Quantity of heat (Q) is the energy that a body receives or gives off during the process of heat transfer. Specific heat capacity (c) is the amount of heat required to heat 1 kg of a substance by 1°C. Unit of measurement – J/kg°C. The formula for calculating the amount of heat required to heat a body and released by it during cooling: Q=cm(t 2 -t 1), where m is body mass, t 1 is the initial body temperature, t 2 is the final body temperature.
Combustion Combustion is the process of combining carbon atoms with two oxygen atoms, which produces carbon dioxide and releases energy. Specific heat of combustion of fuel (q) is a physical quantity showing how much heat will be released during complete combustion of 1 kg of fuel. Formula for calculating the amount of heat released during complete combustion of fuel: Q=qm.
Melting Melting is the process of transition of a substance from a solid to a liquid state. Crystallization is the process of transition of a substance from a liquid to a solid state. Melting point is the temperature at which a substance melts (does not change during melting). Specific heat of fusion () is a physical quantity showing how much heat is required to convert 1 kg of a crystalline substance taken at the melting point into a liquid of the same temperature. Formula for calculating the amount of heat required to melt a crystalline body taken at the melting point and released by it during solidification: Q = m.
Evaporation Evaporation is vaporization that occurs from the surface of a liquid (occurs at any temperature). Boiling is an intense transition of liquid into vapor, accompanied by the formation of vapor bubbles throughout the entire volume of the liquid and their subsequent floating to the surface (occurs at a temperature specific for each substance). Specific heat of vaporization (L) is the amount of heat required to convert a liquid weighing 1 kg, taken at boiling point, into steam. Formula for calculating the amount of heat required to transform a liquid of any mass taken at the boiling point into vapor: Q = Lm.
Physical process Explanation from a molecular point of view Explanation from an energy point of view Formula for calculating the amount of heat Physical constants 1. heating The speed of movement of molecules increases Energy is absorbed Q=cm(t 2 -t 1) s – specific heat capacity, J/kg°C 2. cooling The speed of movement of molecules decreases Energy is released Q=cm(t 2 -t 1); Q 0 3. melting The crystal lattice of a solid is destroyed Energy is absorbed Q= m - specific heat of fusion, J/kg 4. crystallization Restoration of the crystal lattice Energy is released Q=- m 5. evaporation Bonds between liquid molecules are broken Energy is absorbed Q=Lm L – specific heat of vaporization, J/kg 6. condensation Return of vapor molecules to liquid Energy released Q=-Lm 7. combustion of fuel C+O 2 CO 2 Energy released Q=qm q – specific heat of combustion of fuel, J/kg
