Ways to change internal energy - Hypermarket of knowledge. Methods for changing internal energy and their description

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..

Thus, 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. Zoom internal energy body while working 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.

Hence, 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. Air and various items the room is 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. Kinetic energy molecules hot water more 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 more high 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

1. Using Figure 3, describe how the internal energy of a body changes when work is done on it.
2. Describe an experiment showing that a body can do work due to internal energy.
3. Give examples of changes in the internal energy of a body by means of heat transfer.
4. Explain, on the basis of the molecular structure of a substance, the heating of a knitting needle dipped in hot water.
5. What is heat transfer?
6. What are two ways to change the internal energy of a body?

Exercise 2

1. 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?
2. 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.

Internal energy of the body cannot be a constant. It can change in any body. If you increase the body temperature, then its internal energy will increase, because. the average speed of the molecules will increase. Thus, the kinetic energy of the molecules of the body increases. Conversely, as the temperature decreases, the internal energy of the body decreases.

We can conclude: the internal energy of the body changes if the speed of the molecules changes. Let's try to determine by what method it is possible to increase or decrease the speed of movement of molecules. Consider the following experience. We fix a thin-walled brass tube on the stand. Fill the tube with ether and close it with a cork. Then we tie it with a rope and begin to intensively move the rope in different sides. Later certain time, the ether will boil, and the force of the steam will push the cork out. Experience shows that the internal energy of a substance (ether) has increased: after all, it has changed its temperature, while boiling.

The increase in internal energy occurred due to the work done when rubbing the tube with a rope.

As we know, heating of bodies can also occur during impacts, flexion or extension, in other words, during deformation. In all the given examples, the internal energy of the body increases.

Thus, the internal energy of the body can be increased by doing work on the body.

If the work is done by the body itself, its internal energy decreases.

Let's consider another experience.

In a glass vessel, which has thick walls and is closed with a cork, we pump air through a specially made hole in it.

After some time, the cork will fly out of the vessel. At the moment when the cork flies out of the vessel, we can see the formation of fog. Therefore, its formation means that the air in the vessel has become cold. Compressed air, which is in the vessel, when pushing the cork out, does a certain amount of work. This work he performs at the expense of his internal energy, which at the same time is reduced. It is possible to draw conclusions about the decrease in internal energy based on the cooling of the air in the vessel. Thus, the internal energy of the body can be changed by making certain work.

However, internal energy can be changed in another way, without doing work. Consider an example, water in a kettle that is on the stove boils. The air, as well as other objects in the room, are heated by a central radiator. IN similar cases, the internal energy increases, because body temperature increases. But the work is not done. So we conclude a change in internal energy can occur not due to the performance of a certain work.

Let's consider one more example.

Dip a metal needle into a glass of water. The kinetic energy of hot water molecules is greater than the kinetic energy of cold metal particles. Hot water molecules will transfer part of their kinetic energy to cold metal particles. Thus, the energy of the water molecules will decrease in a certain way, while the energy of the metal particles will increase. The temperature of the water will drop, and the temperature of the spokes slowly, will increase. In the future, the difference between the temperature of the needle and the water will disappear. Due to this experience, we saw a change in internal energy various bodies. We conclude: the internal energy of various bodies changes due to heat transfer.

The process of converting internal energy without performing a certain work on the body or the body itself is called heat transfer.

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In the article below, we will talk about internal energy and how to change it. Here we will get acquainted with common definition VE, with its meaning and two types of change of state by the energy possessed by a physical body, an object. 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 combination of a number of system components full energy 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, there is a transformation of the mechanical energy resource into internal type the energy that an object has. 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 is an increase/decrease 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 specific case will be few. 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.

How to change the mechanical energy of the body? Yes, very simple. Change its location or give it acceleration. For example, kick the ball or lift it higher off the ground.

In the first case, we will change its kinetic energy, in the second, potential. But what about internal energy? How to change the internal energy of the body? To begin with, let's figure out what it is. Internal energy is the kinetic and potential energy of all the particles that make up the body. In particular, the kinetic energy of particles is the energy of their motion. And the speed of their movement, as you know, depends on temperature. That is, the logical conclusion is that by raising the body temperature, we will increase its internal energy. The easiest way to increase body temperature is through heat transfer. Upon contact of bodies with different temperatures a colder body heats up at the expense of a warmer one. The warmer body in this case cools down.

A simple daily example: a cold spoon in a cup of hot tea heats up very quickly, while the tea cools down a little. An increase in body temperature is possible in other ways. What do we all do when our face or hands freeze outside? We three of them. When rubbed, objects heat up. Also, objects heat up during impacts, pressure, that is, in other words, during interaction. Everyone knows how fire was made in ancient times - they either rubbed pieces of wood against each other, or knocked flint on another stone. Also in our time, flint lighters use the friction of a metal rod on flint.

So far, we have been talking about changing the internal energy by changing the kinetic energy of its constituent particles. What about the potential energy of these same particles? As you know, the potential energy of particles is the energy of their relative position. Thus, to change the potential energy of the particles of the body, we need to deform the body: compress, twist, and so on, that is, change the location of the particles relative to each other. This is achieved by influencing the body. We change speed separate parts body, that is, we do work on it.

Examples of changes in internal energy

Thus, all cases of influence on the body in order to change its internal energy are achieved in two ways. Either by transferring heat to it, that is, by heat transfer, or by changing the speed of its particles, that is, by performing work on the body.

Examples of changes in internal energy- this is almost all the processes taking place in the world. The internal energy of particles does not change in the case when absolutely nothing happens to the body, which, you will agree, is extremely rare - the law of conservation of energy is in effect. There is something going on around us all the time. Even with objects that at first glance nothing happens, in fact, there are various changes imperceptible to us: slight changes in temperature, small deformations, and so on. The chair sags under our weight, the temperature of the book on the shelf slightly changes with each movement of air, not to mention the drafts. Well, as for living bodies, it is clear without words that something is happening inside them all the time, and the internal energy changes almost at every moment of time.

If you pump into a thick-walled jar closed with a cork, the bottom of which is covered with water, then after some time the cork will fly out of the jar and fog will form in the jar. The cork flew out of the can, because the air in there acted on it with a certain force. The air at the exit of the cork did the work. It is known that a body can perform work if it has energy. Therefore, the air in the jar has energy.

When the air did work, its temperature dropped, and its state changed. Wherein mechanical energy air has not changed: neither its speed nor its position relative to the Earth have changed. Therefore, the work was done not due to mechanical, but due to other energy. This energy is the internal energy of the air in the jar.

Internal energy body is the sum of the kinetic energy of the movement of its molecules and the potential energy of their interaction. kinetic energy ( Ek) molecules have, since they are in motion, and potential energy (Ep) as they interact. Internal energy is denoted by the letter U. The unit of internal energy is 1 joule. (1 J). U = Ek + En.

Ways to change internal energy

The greater the speed of movement of molecules, the higher the temperature of the body, therefore, the internal energy depends on body temperature . To transfer a substance from a solid state to a liquid state, for example, to turn ice into water, you need to bring energy to it. Therefore, water will have more internal energy than ice of the same mass, and, consequently, the internal energy depends on the aggregate state of the body .

Internal energy can be changed when doing work . If a piece of lead is hit several times with a hammer, then even by touch it can be determined that the piece of lead will heat up. Consequently, its internal energy, as well as the internal energy of the hammer, increased. This happened because work had been done on a piece of lead.

If the body itself does work, then its internal energy decreases, and if work is done on it, then its internal energy increases.

If in a glass of cold water pour hot water, the temperature of the hot water will drop, and cold water- rise. In the considered example, mechanical work is not performed, the internal energy of the bodies changes by heat transfer, as evidenced by a decrease in its temperature.

Hot water molecules have more kinetic energy than cold water molecules. This energy is transferred by hot water molecules to cold water molecules during collisions, and the kinetic energy of cold water molecules increases. The kinetic energy of hot water molecules decreases in this case.

Heat transfer- this is a way of changing the internal energy of the body when energy is transferred from one part of the body to another or from one body to another without doing work.