You see a rocket taking off. She does the work - lifts the astronauts and cargo. The kinetic energy of the rocket increases, as the rocket gains more and more speed as it rises. The potential energy of the rocket also increases, as it rises higher and higher above the Earth. Therefore, the sum of these energies, that is the mechanical energy of the rocket also increases.

We remember that when the body does work, its energy decreases. However, the rocket does work, but its energy does not decrease, but increases! What is the solution to the contradiction? It turns out that in addition to mechanical energy, there is another type of energy - internal energy. It is due to a decrease in the internal energy of the burning fuel that the rocket makes mechanical work and, in addition, increases its mechanical energy.

Not only combustible, but also hot bodies have internal energy that can easily be converted into mechanical work. Let's do an experiment. We heat a weight in boiling water and put it on a tin box attached to a pressure gauge. As the air in the box warms up, the fluid in the pressure gauge will begin to move (see figure).

The expanding air does work on the fluid. Due to what energy does this happen? Of course, due to the internal energy of the kettlebell. Therefore, in this experiment we observe the conversion of the internal energy of the body into mechanical work. Note that the mechanical energy of the weight in this experiment does not change - it is always equal to zero.

So, internal energy- this is such an energy of the body, due to which mechanical work can be performed, while not causing a decrease in the mechanical energy of this body.

The internal energy of any body depends on many reasons: the type and state of its substance, the mass and temperature of the body, and others. All bodies have internal energy: large and small, hot and cold, solid, liquid and gaseous.

The most easily used for human needs is the internal energy of only, figuratively speaking, hot and combustible substances and bodies. These are oil, gas, coal, geothermal sources near volcanoes and so on. In addition, in the 20th century, man learned to use the internal energy of the so-called radioactive substances. These are, for example, uranium, plutonium and others.

Look at the right side of the diagram. The popular literature often mentions thermal, chemical, electrical, atomic (nuclear) and other types of energy. All of them, as a rule, are varieties of internal energy, since they can be used to perform mechanical work without causing a loss of mechanical energy. We will consider the concept of internal energy in more detail in the further study of physics.

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. At the same time, the mechanical energy of the air did not change: neither its speed nor its position relative to the Earth 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 kinetic energy the motion of its molecules and the potential energy of their interaction. kinetic energy ( Ek) molecules have, since they are in motion, and potential energy ( En) 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 hot water is poured into a glass of cold water, the temperature of the hot water will decrease and that of the cold water will increase. 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.

Internal energy is the energy of movement and interaction of molecules.

The kinetic energy of all the molecules that make up the body, and the potential energy of their interaction are internal energy of the body.

When the body stops, the mechanical movement stops, but the random (thermal) movement of its molecules increases. mechanical energy converted into internal energy of the body

Internal energydepends on body temperature, state of aggregation of the substance and other factors.

The internal energy of a body does not depend on the mechanical movement of the body, nor on the position of this body relative to other bodies.

If we consider the kinetic and potential energy one molecule, then this is a very small value, because the mass of the molecule is small. Since the body contains many molecules, the internal energy of the body, equal to the sum of the energies of all molecules, will be large.

Ways to change internal energy

When the temperature rises, the internal energy of the body increases, as the average speed of movement of the molecules of this body increases. Conversely, as the temperature decreases, the internal energy of the body decreases.

Experience: If you heat a bottle with a rubber stopper, the cork will fly out after a while.

Thus, the internal energy of the body changes when the speed of the molecules changes.

Internal energy can be changed in two ways:

1) doing mechanical work. Internal energy increases if work is done on the body, and decreases if work is done on the body.

2) by heat transfer (thermal conduction, convection, radiation). If the body gives off heat, then the internal energy decreases, and if it receives heat, then it increases.

Types of heat transfer. Experiments illustrating the types of heat transfer. Heat transfer in nature, technology, mechanics.

Heat transfer (heat transfer) is a process of change in internal energy that occurs without doing work.

1)

Thermal conductivity - a type of heat transfer in which energy is transferred from one body to another upon contact or from one part of it to another. Different substances have different thermal conductivity. The thermal conductivity of metals is high, that of liquids is less, that of gases is low. With heat conduction, there is no transfer of matter.

2) Convection- a type of heat transfer in which energy is transferred by jets of gas and liquid. There are two types of convection: natural and forced. There is no convection in solids, since their particles do not have high mobility. Many manifestations of convection can be found in nature and human life. Convection also finds application in engineering.

3) Radiation A type of heat transfer in which energy is transferred by electromagnetic waves. Bodies with a dark surface absorb and radiate energy better than bodies with a light surface. This is used in practice.

* During heat exchange, the amount of heat given off is equal in absolute value to the amount of heat received, or their sum is equal to zero. This is called the heat balance level.

All the macroscopic bodies around us have particles in their composition: atoms or molecules. Being in constant motion, they simultaneously possess two types of energy: kinetic and potential and form the internal energy of the body:

U = ∑ E k + ∑ E p

This concept also includes the energy of interaction with each other of electrons, protons, neutrons.

Is it possible to change the internal energy

There are 3 ways to change it:

• due to the heat transfer process;
• by doing mechanical work;
• through chemical reactions.

Let's consider in more detail all the options.

If work is done by the body itself, then its internal energy will decrease, and when work is done on the body, its internal energy will increase.

The simplest examples of increasing energy are cases of making fire with the help of friction:

• with the use of tinder;
• with the help of a flint;
• using matches.

Thermal processes associated with temperature changes are also accompanied by changes in internal energy. If a body is heated, its energy will increase.

The result of chemical reactions is the transformation of substances that differ from each other in structure and composition. For example, in the process of fuel combustion, after the combination of hydrogen with oxygen, carbon monoxide is formed. When hydrochloric acid is combined with zinc, hydrogen will be released, and as a result of the combustion of hydrogen, water vapor will be released.

The internal energy of the body will also change due to the transfer of electrons from one electron shell to another.

Energy of bodies - dependence and characteristics

Internal energy is a characteristic of the thermal state of the body. It depends on:

• state of aggregation, and changes during boiling and evaporation, crystallization or condensation, melting or sublimation;
• body weight;
• body temperature characterizing the kinetic energy of particles;
• kind of substance.

Internal energy of a monatomic ideal gas

This energy, ideally, is the sum of the kinetic energies of each particle, which is randomly and continuously moving, and the potential energy of their interaction within a particular body. This happens due to a change in temperature, which is confirmed by Joule's experiments.

To calculate the internal energy of a monatomic gas, use the equation:

Where, depending on the change in temperature, the internal energy will change (increase with an increase in temperature, and decrease with its decrease). Internal energy is a state function.

The internal energy of any body is associated with the movement and state of the particles (molecules, atoms) of the substance. If the total energy of the body is known, then the internal energy can be found by excluding from the total the motion of the entire body as a macroscopic object, as well as the energy of interaction of this body with potential fields.

Also, internal energy contains the energy of vibrations of molecules and the potential energy of intermolecular interaction. If we are talking about an ideal gas, then the main contribution to the internal energy comes from the kinetic component. The total internal energy is equal to the sum of the energies of individual particles.

As you know, the kinetic energy of the translational motion of a material point, which models a particle of matter, strongly depends on the speed of its movement. It is also worth noting that the energy of oscillatory and rotational movements depends on their intensity.

Recall from the course of molecular physics the formula for the internal energy of an ideal monatomic gas. It is expressed in terms of the sum of the kinetic components of all gas particles, which can be averaged. Averaging over all particles leads to an explicit dependence of the internal energy on the temperature of the body, as well as on the number of degrees of freedom of the particles.

In particular, for a monatomic ideal gas, whose particles have only three degrees of freedom of translational motion, the internal energy turns out to be directly proportional to three-seconds of the product of the Boltzmann constant and temperature.

Temperature dependence

So, the internal energy of the body actually reflects the kinetic energy of the movement of particles. In order to understand what is the relationship of this energy with temperature, it is necessary to determine the physical meaning of the temperature value. If you heat a vessel filled with gas and having movable walls, then its volume will increase. This indicates that the pressure inside has increased. The pressure of the gas is created due to the impact of particles on the walls of the vessel.

Since the pressure has increased, it means that the impact force has also increased, which indicates an increase in the speed of movement of molecules. Thus, an increase in the temperature of the gas led to an increase in the speed of the molecules. This is the essence of the temperature value. Now it becomes clear that an increase in temperature, leading to an increase in the speed of particles, entails an increase in the kinetic energy of intramolecular motion, and hence an increase in internal energy.