To solve practical issues, it is not the internal energy itself that plays a significant role, but its change Δ U = U 2 - U one . The change in internal energy is calculated based on the laws of conservation of energy.
The internal energy of a body can change in two ways:
1. When making mechanical work.
a) If an external force causes deformation of the body, then the distances between the particles of which it consists change, and consequently, the potential energy of the interaction of particles changes. With inelastic deformations, in addition, the temperature of the body changes, i.e. the kinetic energy of the thermal motion of particles changes. But when the body is deformed, work is done, which is a measure of the change in the internal energy of the body.
b) The internal energy of a body also changes during its inelastic collision with another body. As we saw earlier, during inelastic collision of bodies, their kinetic energy decreases, it turns into internal energy (for example, if you hit a wire lying on an anvil several times with a hammer, the wire will heat up). The measure of change in the kinetic energy of a body is, according to the kinetic energy theorem, the work of the acting forces. This work can also serve as a measure of changes in internal energy.
c) The change in the internal energy of the body occurs under the action of the force of friction, since, as is known from experience, friction is always accompanied by a change in the temperature of rubbing bodies. The work of the friction force can serve as a measure of the change in internal energy.
2. Using heat transfer. For example, if a body is placed in a burner flame, its temperature will change, and therefore its internal energy will also change. However, no work was done here, because there was no visible movement of either the body itself or its parts.
The change in the internal energy of a system without doing work is called heat exchange(heat transfer).
There are three types of heat transfer: conduction, convection and radiation.
a) thermal conductivity is the process of heat exchange between bodies (or body parts) in their direct contact, due to the thermal chaotic movement of body particles. The amplitude of oscillations of the molecules of a solid body is greater, the higher its temperature. The thermal conductivity of gases is due to the exchange of energy between gas molecules during their collisions. In the case of liquids, both mechanisms work. The thermal conductivity of a substance is maximum in the solid state and minimum in the gaseous state.
b) Convection is the transfer of heat by heated flows of liquid or gas from one part of the volume they occupy to another.
c) Heat transfer at radiation carried out at a distance by means of electromagnetic waves.
Let us consider in more detail how to change the internal energy.
Quantity of heat
As you know, during various mechanical processes, there is a change in mechanical energy W. The measure of change in mechanical energy is the work of forces applied to the system:
During heat transfer, a change in the internal energy of the body occurs. The measure of change in internal energy during heat transfer is the amount of heat.
Quantity of heat is a measure of the change in internal energy during heat transfer.
Thus, both work and the amount of heat characterize the change in energy, but are not identical to internal energy. They do not characterize the state of the system itself (as internal energy does), but determine the process of energy transition from one form to another (from one body to another) when the state changes and essentially depend on the nature of the process.
The main difference between work and heat is that
§ work characterizes the process of changing the internal energy of the system, accompanied by the transformation of energy from one type to another (from mechanical to internal);
§ the amount of heat characterizes the process of transferring internal energy from one body to another (from hotter to less hot), not accompanied by energy transformations.
§ Heat capacity, the amount of heat expended to change the temperature by 1 ° C. According to a stricter definition, heat capacity- thermodynamic quantity, determined by the expression:
§ where Δ Q- the amount of heat communicated to the system and caused a change in its temperature by Delta;T. Finite difference ratio Δ Q/ΔT is called the average heat capacity, the ratio of infinitesimal values d Q/dT- true heat capacity. Because d Q is not a total differential of the state function, then heat capacity depends on the transition path between two states of the system. Distinguish heat capacity system as a whole (J/K), specific heat capacity[J/(g K)], molar heat capacity[J/(mol K)]. All formulas below use molar values heat capacity.
Question 32:
Internal energy can be changed in two ways.
The amount of heat (Q) is the change in the internal energy of the body that occurs as a result of heat transfer.
The amount of heat is measured in the SI system in joules.
[Q] = 1J.
The specific heat capacity of a substance shows how much heat is needed to change the temperature of a unit mass of a given substance by 1°C.
Unit of specific heat capacity in the SI system:
[c] = 1J/kg degrees C.
Question 33:
33
The first law of thermodynamics, the amount of heat received by the system goes to changing its internal energy and doing work on external bodies. dQ=dU+dA, where dQ is the elementary amount of heat, dA is the elementary work, dU is the increase in internal energy. Application of the first law of thermodynamics to isoprocesses
Among the equilibrium processes that occur with thermodynamic systems, there are isoprocesses, at which one of the main state parameters is kept constant.
Isochoric process (V= const). Diagram of this process (isochore) in coordinates R, V is depicted as a straight line parallel to the y-axis (Fig. 81), where the process 1-2
is isochoric heating, and 1
-3 -
isochoric cooling. In an isochoric process, the gas does no work on external bodies, 
Isothermal process (T= const). As already mentioned § 41, the isothermal process is described by the Boyle-Mariotte law
, so that the temperature does not decrease during the expansion of the gas, it is necessary to supply the gas with an amount of heat equivalent to the external work of expansion during the isothermal process.
Question 34:
34 Adiabatic is called a process in which there is no heat exchange ( dQ= 0) between the system and the environment. Adiabatic processes include all fast processes. For example, the process of propagation of sound in a medium can be considered an adiabatic process, since the speed of propagation of a sound wave is so high that the exchange of energy between the wave and the medium does not have time to occur. Adiabatic processes are used in internal combustion engines (expansion and compression of the combustible mixture in cylinders), in refrigeration units, etc.
From the first law of thermodynamics ( dQ= d U+dA) for an adiabatic process it follows that 
p /С V =γ , we find
Integrating the equation in the range from p 1 to p 2 and, accordingly, from V 1 to V 2, and potentiating, we arrive at the expression
Since states 1 and 2 are chosen arbitrarily, we can write
Internal energy can be changed in two ways.
If work is done on a body, its internal energy increases.
Internal energy of the body(denoted as E or U) is the sum of the energies of molecular interactions and thermal motions of a molecule. The internal energy is a single-valued function of the state of the system. This means that whenever a system finds itself in a given state, its internal energy assumes the value inherent in this state, regardless of the system's history. Consequently, the change in internal energy during the transition from one state to another will always be equal to the difference between its values in the final and initial states, regardless of the path along which the transition was made.
The internal energy of a body cannot be measured directly. Only the change in internal energy can be determined:
This formula is a mathematical expression of the first law of thermodynamics
For quasi-static processes, the following relationship holds:
Temperature measured in Kelvin
Entropy, measured in joules/kelvin
Pressure measured in pascals
Chemical potential
Number of particles in systems
Heat of combustion of fuel. conditional fuel. The amount of air needed to burn the fuel.
The quality of a fuel is judged by its calorific value. To characterize solid and liquid fuels, the specific calorific value is used, which is the amount of heat released during the complete combustion of a unit mass (kJ / kg). For gaseous fuels, the volumetric calorific value is used, which is the amount of heat released during the combustion of a unit volume (kJ / m3). In addition, gaseous fuel in some cases is estimated by the amount of heat released during the complete combustion of one mole of gas (kJ / mol).
The heat of combustion is determined not only theoretically, but also empirically, by burning a certain amount of fuel in special devices called calorimeters. The heat of combustion is estimated by the increase in water temperature in the colorimeter. The results obtained by this method are close to the values calculated from the elemental composition of the fuel.
Question 14Change in internal energy during heating and cooling. The work of gas with a change in volume.
The internal energy of the body depends on the average kinetic energy of its molecules, and this energy, in turn, depends on temperature. Therefore, by changing the body temperature, we also change its internal energy. When a body is heated, its internal energy increases, and when it cools, it decreases.
The internal energy of the body can be changed without doing work. So, for example, it can be increased by heating a kettle of water on the stove or by lowering a spoon into a glass of hot tea. The fireplace in which the fire is kindled, the roof of the house illuminated by the sun, etc. are heated. An increase in the temperature of bodies in all these cases means an increase in their internal energy, but this increase occurs without doing work.
Change in internal energy body without doing work is called heat transfer. Heat transfer occurs between bodies (or parts of the same body) that have different temperatures.
How, for example, does heat transfer occur when a cold spoon comes into contact with hot water? First, the average speed and kinetic energy of the hot water molecules exceed the average speed and kinetic energy of the metal particles from which the spoon is made. But in those places where the spoon comes into contact with water, the hot water molecules begin to transfer part of their kinetic energy to the particles of the spoon, and they begin to move faster. In this case, the kinetic energy of water molecules decreases, and the kinetic energy of the particles of the spoon increases. Along with the energy, the temperature also changes: the water gradually cools down, and the spoon heats up. The change in their temperature occurs until it becomes the same for both the water and the spoon.
Part of the internal energy transferred from one body to another during heat exchange is denoted by a letter and is called the amount of heat.
Q is the amount of heat.
The amount of heat should not be confused with temperature. Temperature is measured in degrees, and the amount of heat (like any other energy) is measured in joules.
When bodies with different temperatures come into contact, the hotter body gives off a certain amount of heat, and the colder body receives it.
Work at isobaric gas expansion. One of the main thermodynamic processes that take place in most heat engines is the process of gas expansion with the performance of work. It is easy to determine the work done during the isobaric expansion of a gas.
If during the isobaric expansion of gas from volume V1 to volume V2 the piston moves in the cylinder at a distance l (Fig. 106), then the work A "performed by the gas is equal to
Where p is the gas pressure, is the change in its volume.
Work with an arbitrary gas expansion process. An arbitrary process of gas expansion from volume V1 to volume V2 can be represented as a set of alternating isobaric and isochoric processes.
Work with isothermal gas expansion. Comparing the areas of the figures under the sections of the isotherm and isobar, we can conclude that the expansion of gas from volume V1 to volume V2 at the same initial value of gas pressure is accompanied in the case of isobaric expansion by more work.
Work with gas compression. When the gas expands, the direction of the gas pressure force vector coincides with the direction of the displacement vector, so the work A "performed by the gas is positive (A" > 0), and the work A of external forces is negative: A \u003d -A "< 0.
When compressing gas the direction of the external force vector coincides with the direction of movement, therefore the work A of the external forces is positive (A > 0), and the work A "performed by the gas is negative (A"< 0).
adiabatic process. In addition to isobaric, isochoric and isothermal processes, adiabatic processes are often considered in thermodynamics.
An adiabatic process is a process that occurs in a thermodynamic system in the absence of heat exchange with surrounding bodies, i.e., under the condition Q = 0.
Question 15 Conditions for the equilibrium of the body. Moment of power. Types of balance.
Equilibrium, or balance, of a number of related phenomena in the natural and human sciences.
A system is considered to be in a state of equilibrium if all influences on this system are compensated by others or are absent altogether. A similar concept is stability. Equilibrium can be stable, unstable or indifferent.
Typical examples of balance:
1. Mechanical equilibrium, also known as static equilibrium, is the state of a body at rest, or moving uniformly, in which the sum of the forces and moments acting on it is zero.
2. Chemical equilibrium - a position in which a chemical reaction proceeds to the same extent as the reverse reaction, and as a result there is no change in the amount of each component.
3. The physical balance of people and animals, which is maintained by understanding its necessity and, in some cases, by artificially maintaining this balance [source not specified 948 days].
4. Thermodynamic equilibrium - the state of the system in which its internal processes do not lead to changes in macroscopic parameters (such as temperature and pressure).
R equality to zero of the algebraic sum moments of forces also does not mean that the body is necessarily at rest. For several billion years, the rotation of the Earth around its axis continues with a constant period precisely because the algebraic sum of the moments of forces acting on the Earth from other bodies is very small. For the same reason, a spinning bicycle wheel continues to rotate at a constant frequency, and only external forces stop this rotation.
Types of balance. In practice, an important role is played not only by the fulfillment of the equilibrium condition for bodies, but also by the qualitative characteristic of equilibrium, called stability. There are three types of balance of bodies: stable, unstable and indifferent. The equilibrium is called stable if, after small external influences, the body returns to its original state of equilibrium. This happens if, with a slight displacement of the body in any direction from the initial position, the resultant of the forces acting on the body becomes non-zero and is directed towards the equilibrium position. In stable equilibrium is, for example, a ball at the bottom of the recess.
The general condition for the equilibrium of a body. Combining the two conclusions, we can formulate a general condition for the equilibrium of a body: a body is in equilibrium if the geometric sum of the vectors of all forces applied to it and the algebraic sum of the moments of these forces about the axis of rotation are equal to zero.
Question 16Vaporization and condensation. Evaporation. Boiling liquid. Dependence of liquid boiling on pressure.
Vaporization - the property of dropping liquids to change their state of aggregation and turn into steam. Vaporization that occurs only on the surface of a dropping liquid is called evaporation. Vaporization over the entire volume of a liquid is called boiling; it occurs at a certain temperature, depending on the pressure. The pressure at which a liquid boils at a given temperature is called saturated vapor pressure pnp, its value depends on the type of liquid and its temperature.
Evaporation- the process of transition of a substance from a liquid state to a gaseous state (steam). The evaporation process is the reverse of the condensation process (transition from a vapor to a liquid state. Evaporation (vaporization), the transition of a substance from a condensed (solid or liquid) phase to a gaseous (steam); first-order phase transition.
Condensation - it is the reverse process of evaporation. During condensation, the vapor molecules return to the liquid. In a closed vessel, a liquid and its vapor can be in a state of dynamic equilibrium when the number of molecules leaving the liquid is equal to the number of molecules returning to the liquid from the vapor, that is, when the rates of evaporation and condensation are the same. Such a system is called a two-phase system. A vapor that is in equilibrium with its liquid is called saturated. The number of molecules emitted from a unit surface area of a liquid in one second depends on the temperature of the liquid. The number of molecules returning from vapor to liquid depends on the concentration of vapor molecules and on the average rate of their thermal motion, which is determined by the temperature of the vapor.
Boiling- the process of vaporization in a liquid (transition of a substance from a liquid to a gaseous state), with the appearance of phase separation boundaries. The boiling point at atmospheric pressure is usually given as one of the main physicochemical characteristics of a chemically pure substance.
Boiling is distinguished by type:
1. boiling with free convection in a large volume;
2. boiling under forced convection;
3. as well as in relation to the average temperature of the liquid to the saturation temperature:
4. boiling of a liquid subcooled to saturation temperature (surface boiling);
5. boiling of a liquid heated to saturation temperature
Bubble
Boiling , in which steam is formed in the form of periodically emerging and growing bubbles, is called nucleate boiling. With slow nucleate boiling in a liquid (more precisely, as a rule, on the walls or at the bottom of the vessel), bubbles filled with vapor appear. Due to the intense evaporation of the liquid inside the bubbles, they grow, float, and the vapor is released into the vapor phase above the liquid. In this case, in the near-wall layer, the liquid is in a slightly overheated state, i.e., its temperature exceeds the nominal boiling point. Under normal conditions, this difference is small (on the order of one degree).
Film
When the heat flux increases to a certain critical value, the individual bubbles merge, forming a continuous vapor layer near the vessel wall, which periodically breaks through into the liquid volume. This mode is called film mode.
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The internal energy of a body is not some kind of constant. In the same body, it can change.
When the temperature rises, the internal energy of the body increases, as the average velocity of the molecules increases.
Consequently, the kinetic energy of the molecules of this body increases. Conversely, as the temperature decreases, the internal energy of the body decreases..
In this way, the internal energy of the body changes with a change in the speed of movement of molecules.
Let's try to figure out how to increase or decrease the speed of the molecules. To do this, we will do the following experiment. We fix the thin-walled brass tube on the stand (Fig. 3). Pour a little ether into the tube and close the cork. Then we wrap the tube with a rope and begin to quickly move it first in one direction, then in the other. After a while, the ether will boil, and the steam will push the cork out. Experience shows that the internal energy of the ether has increased: after all, it has heated up and even boiled.
Rice. 3. An increase in the internal energy of the body when doing work on it
The increase in internal energy occurred as a result of the work done when rubbing the tube with a rope.
Heating of bodies also occurs during impacts, extension and bending, i.e., during deformation. The internal energy of the body in all the above examples increases.
Consequently, the internal energy of a body can be increased by doing work on the body.
If the work is done by the body itself, then it internal, energy decreases.
Let's do the following experiment.
Into a thick-walled glass vessel, closed with a cork, we pump air through a special hole in it (Fig. 4).
Rice. 4. Reducing the internal energy of the body when doing work by the body itself
After a while, the cork will pop out of the vessel. At the moment when the cork pops out of the vessel, fog is formed. Its appearance means that the air in the vessel has become colder. The compressed air in the vessel pushes out the cork and does work. He does this work at the expense of his internal energy, which at the same time decreases. You can judge the decrease in internal energy by cooling the air in the vessel. So, the internal energy of a body can be changed by doing work.
The internal energy of the body can be changed in another way, without doing work. For example, water in a kettle put on the stove boils. The air and various objects in the room are heated by a central heating radiator, the roofs of houses are heated by the rays of the sun, etc. In all these cases, the temperature of the bodies rises, which means that their internal energy increases. But the work is not done.
Means, change in internal energy can occur not only as a result of doing work.
How can the increase in internal energy be explained in these cases?
Consider the following example.
Dip a metal needle into a glass of hot water. The kinetic energy of hot water molecules is greater than the kinetic energy of cold metal particles. Hot water molecules, when interacting with cold metal particles, will transfer part of their kinetic energy to them. As a result, the energy of water molecules will decrease on average, while the energy of metal particles will increase. The temperature of the water will decrease and the temperature of the metal spoke will gradually increase. After a while, their temperatures will even out. This experience demonstrates the change in the internal energy of bodies.
So, internal energy of bodies can be changed by heat transfer.
The process of changing internal energy without doing work on the body or the body itself is called heat transfer.
Heat transfer always occurs in a certain direction: from bodies with a higher temperature to bodies with a lower one.
When the temperatures of the bodies equalize, heat transfer stops.
The internal energy of a body can be changed in two ways: by doing mechanical work or by heat transfer.
Heat transfer, in turn, can be carried out: 1) thermal conductivity; 2) convection; 3) radiation.
Questions
- Using Figure 3, describe how the internal energy of a body changes when work is done on it.
- Describe an experiment showing that a body can do work due to internal energy.
- Give examples of changes in the internal energy of a body by means of heat transfer.
- Explain, on the basis of the molecular structure of a substance, the heating of a knitting needle dipped in hot water.
- What is heat transfer?
- What are two ways to change the internal energy of a body?
Exercise 2
- The force of friction does work on the body. Does this change the internal energy of the body? By what signs can one judge this?
- When you go down the rope quickly, your hands get hot. Explain why this is happening.
Exercise
Place the coin on a sheet of plywood or a wooden board. Press the coin against the board and move it quickly in one direction or the other. Notice how many times you need to move the coin to make it warm, hot. Make a conclusion about the relationship between the work done and the increase in the internal energy of the body.
Therefore, by changing the temperature of the body, we change its internal energy. When a body is heated, its internal energy increases, when it is cooled, it decreases.
Let's do an experiment. We fix a thin-walled brass tube on the stand. Pour a little ether into it and close it tightly with a cork. Now we wrap the pipe with a rope and begin to rub the pipe with it, quickly pulling it into the rope in one direction or the other. After some time, the internal energy of the tube with ether will increase so much that the ether will boil and the resulting vapor will push out the cork (Fig. 60).
This experience shows that the internal energy of the body can be changed by doing work on the body, in particular by friction.
By changing the internal energy of a piece of wood through friction, our ancestors made fire. The ignition temperature of wood is 250 °C. Therefore, to get fire, you need to rub one piece of wood over another until their temperature reaches this value. Is it easy? When the heroes of Jules Verne's novel "The Mysterious Island" tried to make fire in this way, they did not succeed.
“If the energy that Neb and Pencroff spent could be turned into heat, it would probably be enough to heat the boiler of an ocean steamer. But the result of their efforts was zero. Pieces of wood, however, warmed up, but much less than the participants themselves this operation.
After an hour of work, Pencroff was covered in sweat and angrily threw away the pieces of wood, saying:
"Don't tell me that savages make fire this way!" I would rather believe that it snows in summer. It is easier, perhaps, to light your own palms by rubbing them one against the other.
The reason for their failure was that fire had to be made not by simply rubbing one piece of wood against another, but by drilling into a plank with a pointed stick (Fig. 61). Then, with a certain skill, it is possible to increase the temperature in the nest of the stick by 20 ° C in 1 s. And it takes only 250/20=12.5 seconds to bring the stick to the point of burning! 
Many people in our time "produce" fire by friction - by rubbing matches against a matchbox. How long have matches been around? The production of the first (phosphorus) matches began in the 1930s. 19th century Phosphorus ignites at rather low heating - only up to 60 °C. Therefore, in order to light a phosphorus match, it was enough to strike it on almost any surface (starting from the nearest wall and ending with the bootleg). However, these matches were very dangerous: they were poisonous and, due to easy ignition, often caused a fire. Safety matches (which we still use today) were invented in 1855 in Sweden (hence their name "Swedish matches"). The phosphorus in these matches has been replaced by other combustible substances.
Thus, friction can raise the temperature of a substance. Doing work on the body(for example, striking a piece of lead with a hammer, bending and unbending a wire, moving one object over the surface of another, or compressing a gas in a cylinder with a piston), we increase its internal energy. If the body itself does the work " (due to its internal energy), then the internal energy of the body decreases and the body cools.
Let's observe this in experience. Take a thick-walled glass vessel and tightly close it with a rubber stopper with a hole. Through this hole, with the help of a pump, we will begin to pump air into the vessel. After some time, the cork will fly out of the vessel with noise, and fog will appear in the vessel itself (Fig. 62). The appearance of fog means that the air in the vessel has become colder and, consequently, its internal energy has decreased. This is explained by the fact that the compressed air in the vessel, pushing out the cork, did the work by reducing its internal energy. Therefore, the air temperature has dropped.
The internal energy of the body can be changed without doing work. So, for example, it can be increased by heating a kettle of water on the stove or by lowering a spoon into a glass of hot tea. The fireplace in which the fire is kindled, the roof of the house illuminated by the sun, etc. are heated. An increase in the temperature of bodies in all these cases means an increase in their internal energy, but this increase occurs without doing work.
The change in the internal energy of a body without doing work is called heat exchange. Heat transfer occurs between bodies (or parts of the same body) that have different temperatures.
How, for example, does heat transfer occur when a cold spoon comes into contact with hot water? First, the average speed and kinetic energy of the hot water molecules exceed the average speed and kinetic energy of the metal particles from which the spoon is made. But in those places where the spoon comes into contact with water, the hot water molecules begin to transfer part of their kinetic energy to the particles of the spoon, and they begin to move faster. In this case, the kinetic energy of water molecules decreases, and the kinetic energy of the particles of the spoon increases. Along with the energy, the temperature also changes: the water gradually cools down, and the spoon heats up. The change in their temperature occurs until it becomes the same for both the water and the spoon.
Part of the internal energy transferred from one body to another during heat transfer is denoted by a letter and is called amount of heat.
Q is the amount of heat.
The amount of heat should not be confused with temperature. Temperature is measured in degrees, and the amount of heat (like any other energy) is measured in joules.
When bodies with different temperatures come into contact, the hotter body gives off a certain amount of heat, and the colder body receives it.
So, there are two ways to change the internal energy: 1) doing work and 2) heat exchange. When implementing the first of these methods, the internal energy of the body changes by the amount of perfect work A, and when implementing the second of them, by an amount equal to the amount of transferred heat Q
Interestingly, both considered methods can lead to exactly the same results. Therefore, according to the final result, it is impossible to determine which of these methods it was achieved. So, taking a heated steel needle from the table, we will not be able to say in what way it was heated - by friction or by contact with a hot body. In principle, it could be either one or the other.
1. Name two ways to change the internal energy of the body. 2. Give examples of increasing the internal energy of the body by doing work on it. 3. Give examples of the increase and decrease in the internal energy of the body as a result of heat transfer. 4. What is the amount of heat? How is it designated? 5. In what units is the amount of heat measured? 6. In what ways can fire be made? 7. When did the production of matches begin?
Press a coin or piece of foil against cardboard or some kind of board. Having made first 10, then 20, etc. movements in one direction or the other, notice what happens to the temperature of the bodies in the process of friction. How does the change in the internal energy of a body depend on the amount of work done?
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Lesson content lesson summary support frame lesson presentation accelerative methods interactive technologies Practice tasks and exercises self-examination workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures graphics, tables, schemes humor, anecdotes, jokes, comics parables, sayings, crossword puzzles, quotes Add-ons abstracts articles chips for inquisitive cheat sheets textbooks basic and additional glossary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in the textbook elements of innovation in the lesson replacing obsolete knowledge with new ones Only for teachers perfect lessons calendar plan for the year methodological recommendations of the discussion program Integrated LessonsIn the article below, we will talk about internal energy and how to change it. Here we will get acquainted with the general definition of SE, with its meaning and two types of change in the state of energy, which a physical body, an object, possesses. In particular, the phenomenon of heat transfer and the performance of work will be considered.
Introduction
Internal energy is that part of the resource of a thermodynamic system that is not dependent on a specific reference system. It can change its meaning within the problem under study.
Characteristics of equal value in the frame of reference, in relation to which the central mass of a body/object of macroscopic dimensions is a state of rest, have the same total and internal energies. They always match. The set of parts that make up the total energy included in the internal energy is not constant and depends on the conditions of the problem being solved. In other words, renewable energy is not a specific type of energy resource. It is a general set of a number of components of the total energy system, which vary according to specific situations. Methods for changing internal energy are based on two basic principles: heat transfer and work.
SE is a specific concept for systems of a thermodynamic nature. It allows physics to use various quantities, such as temperature and entropy, the dimension of the chemical potential, the mass of substances that form the system.
Completing of the work
There are two ways to change the internal energy of a body(s). The first is formed due to the process of performing direct work on the object. The second is the phenomenon of heat transfer.
In cases where the work is done by the body itself, its internal energy index will decrease. When the process is completed by someone or something above the body, then its VE will increase. At the same time, a transformation of a mechanical energy resource into an internal type of energy that an object possesses is observed. Everything can also flow and vice versa: mechanical to internal.
Heat transfer increases the value of SE. However, if the body cools down, then the energy will decrease. With constant maintenance of heat transmission, the indicator will increase. The compression of gases is an example of an increase in the SE index, and their expansion (of gases) is a consequence of a decrease in the value of internal energy.
heat transfer phenomenon
The change in internal energy by the method of heat transfer represents an increase/decrease in the energy potential. It is possessed by the body, without carrying out a certain (in particular mechanical) work. The transferred amount of energy is called heat (Q, J), and the process itself is subject to the universal ZSE. Making changes in VE is always reflected by an increase or decrease in the temperature of the body itself.
Both methods of changing internal energy (work and heat transfer) can be performed with respect to one object in a simultaneous order, i.e., they can be combined.
You can change the SE, for example, by creating friction. Here, the performance of mechanical work (friction) and the phenomenon of heat transfer are clearly monitored. Our ancestors tried to make fire in a similar way. They created friction between the wood, the ignition temperature of which corresponds to 250 ° C.
The change in the internal energy of the body through the performance of work or heat transfer can occur in the same period of time, i.e., these two types of means can work together. However, simple friction in a particular case will not be enough. To do this, one branch had to be sharpened. At present, a person can get fire by rubbing matches, the heads of which are covered with a combustible substance that ignites at 60-100 ° C. The first such products began to be created in the 30s of the XIX century. These were phosphorus matches. They are able to catch fire at a relatively low temperature - 60 ° C. Currently enjoying which were put into production in 1855.
Energy dependency
Speaking about the ways of changing the internal energy, it will be important to mention also the dependence of this indicator on temperature. The fact is that the amount of this energy resource is determined by the average value of the kinetic energy concentrated in the molecule of the body, which, in turn, directly depends on the temperature indicator. It is for this reason that a change in temperature always leads to a change in SE. It also follows from this that heating leads to an increase in energy, and cooling causes it to decrease.
Temperature and heat transfer
Ways to change the internal energy of the body are divided into: heat transfer and mechanical work. However, it will be important to know that the amount of heat and temperature are not the same thing. These concepts should not be confused. Temperature quantities are specified in degrees, and the amount of heat transferred or transferred is specified using joules (J).
The contact of two bodies, one of which will be hot, always leads to the loss of heat by one (hotter) and to its acquisition by the other (colder).
It is important to note that both ways of changing the VE of the body always lead to the same results. It is impossible to determine in what way its change was achieved by the final state of the body.
