In the world around us, various kinds of physical phenomena occur that are directly related to change in body temperature. Since childhood, we have known that cold water, when heated, first becomes barely warm and only after a certain time becomes hot.
With words like “cold”, “hot”, “warm”, we define varying degrees“heating” of bodies, or, speaking in the language of physics, different temperatures tel. Temperature warm water slightly higher than cool water temperature. If you compare the temperature of summer and winter air, the difference in temperature is obvious.
Body temperature is measured using a thermometer and expressed in degrees Celsius (°C).
As is known, diffusion at more high temperature happens faster. It follows from this that the speed of movement of molecules and temperature are deeply interrelated. If you increase the temperature, the speed of movement of molecules will increase, if you decrease it, it will decrease.
Thus, we conclude: body temperature directly depends on the speed of movement of molecules.
Hot water consists of exactly the same molecules as cold water. The difference between them is only in the speed of movement of the molecules.
Phenomena that relate to heating or cooling of bodies and temperature changes are called thermal. These include heating or cooling air, melting metal, and melting snow.
Molecules, or atoms, which are the basis of all bodies, are in endless chaotic motion. The number of such molecules and atoms in the bodies around us is enormous. A volume equal to 1 cm³ of water contains approximately 3.34 · 10²² molecules. Any molecule has a very complex trajectory of movement. For example, gas particles moving at high speeds in different directions can collide with each other and with the walls of the container. Thus, they change their speed and continue moving again.
Figure 1 shows the random movement of paint particles dissolved in water.
Thus, we draw another conclusion: The chaotic movement of particles that make up bodies is called thermal motion.
Chaoticity is the most important feature thermal movement. One of the most important proofs of molecular motion is diffusion and Brownian motion.(Brownian motion is the movement of tiny solid particles in a liquid under the influence of molecular impacts. As observation shows, Brownian motion cannot stop).
In liquids, molecules can vibrate, rotate, and move relative to other molecules. If we take solids, then their molecules and atoms vibrate around certain average positions.
Absolutely all molecules of the body participate in the thermal movement of molecules and atoms, which is why with a change in thermal movement, the state of the body itself and its various properties also change. Thus, if you increase the temperature of ice, it begins to melt, taking on a completely different form - ice becomes liquid. If, on the contrary, you lower the temperature of, for example, mercury, then it will change its properties and turn from a liquid into a solid.
T 
The body temperature directly depends on the average kinetic energy of the molecules. We draw an obvious conclusion: the higher the temperature of a body, the greater the average kinetic energy of its molecules. And, conversely, as the body temperature decreases, the average kinetic energy of its molecules decreases.
If you still have questions or want to learn more about thermal motion and temperature, register on our website and get help from a tutor.
Still have questions? Don't know how to do your homework?
To get help from a tutor, register.
The first lesson is free!
website, when copying material in full or in part, a link to the source is required.
IN this lesson The concept of thermal motion and such a physical quantity as temperature is considered.
Thermal phenomena in human life occupy great importance. We encounter them both during weather forecasts and during boiling. ordinary water. Thermal phenomena are associated with such processes as the creation of new materials, the melting of metals, the combustion of fuel, the creation of new types of fuel for cars and aircraft, etc.
Temperature is one of the the most important concepts associated with thermal phenomena, since often it is temperature that is the most important characteristic of the occurrence of thermal processes.
Definition.Thermal phenomena- these are phenomena associated with heating or cooling of bodies, as well as with changes in their state of aggregation (Fig. 1).
Rice. 1. Ice melting, water heating and evaporation
All thermal phenomena are associated with temperature.
All bodies are characterized by the state of their thermal equilibrium. The main characteristic thermal equilibrium is temperature.
Definition.Temperature- this is a measure of the “warmth” of the body.
Since temperature is a physical quantity, it can and should be measured. To measure temperature, a device called thermometer(from Greek thermo- "warm", metreo- “measuring”) (Fig. 2).
Rice. 2. Thermometer
The first thermometer (or rather, its analogue) was invented by Galileo Galilei (Fig. 3).
Rice. 3. Galileo Galilei (1564-1642)
Galileo's invention, which he presented to his students at university lectures at the end of the 16th century (1597), was called thermoscope. The operation of any thermometer is based on the following principle: physical properties substances change depending on temperature.
Galileo's experiment was as follows: he took a flask with a long stem and filled it with water. Then he took a glass of water and turned the flask upside down, placing it in the glass. Some of the water naturally poured out, but as a result a certain level of water remained in the leg. If you now heat the flask (which contains air), the water level will drop, and if you cool it, then, on the contrary, it will rise. This is due to the fact that when heated, substances (in particular, air) tend to expand, and when cooled, they tend to contract (this is why the rails are not continuous, and the wires between the posts sometimes sag a little).
Rice. 4. Galileo's experiment
This idea formed the basis of the first thermoscope (Fig. 5), which made it possible to evaluate temperature changes (it is impossible to accurately measure temperature with such a thermoscope, since its readings will greatly depend on atmospheric pressure).
Rice. 5. Copy of Galileo's thermoscope
At the same time, the so-called degree scale was introduced. The word itself degree translated from Latin means “step”.
To date, three main scales have been preserved.
1. Celsius
The most widely used scale is one that everyone has known since childhood - the Celsius scale.
Anders Celsius (Fig. 6) is a Swedish astronomer who proposed the following temperature scale: - boiling point of water; - freezing temperature of water. Nowadays we are all accustomed to the inverted Celsius scale.
Rice. 6 Andres Celsius (1701-1744)
Note: Celsius himself said that this choice of scale was caused by a simple fact: but in winter there will be no negative temperature.
2. Fahrenheit scale
In England, USA, France, Latin America and some other countries, the Fahrenheit scale is popular.
Gabriel Fahrenheit (Fig. 7) is a German researcher and engineer who first used his own scale for making glass. The Fahrenheit scale is more subtle: in terms of dimension, a degree on the Fahrenheit scale is smaller than a degree on the Celsius scale.
Rice. 7 Gabriel Fahrenheit (1686-1736)
3. Reaumur scale
The technical scale was invented by the French researcher R.A. Reaumur (Fig. 8). According to this scale, it corresponds to the freezing temperature of water, but Reaumur chose a temperature of 80 degrees as the boiling point of water.
Rice. 8. René Antoine Reaumur (1683-1757)
In physics, the so-called absolute scale - Kelvin scale(Fig. 8). 1 degree Celsius is equal to 1 degree Kelvin, but the temperature in corresponds approximately (Fig. 9).
Rice. 9. William Thomson (Lord Kelvin) (1824-1907)
Rice. 10. Temperature scales
Let us recall that when the temperature of a body changes, its linear dimensions change (when heated, the body expands, when cooled, it contracts). This is due to the behavior of molecules. When heated, the speed of movement of particles increases; accordingly, they begin to interact more often and the volume increases (Fig. 11).
Rice. 11. Changing linear dimensions
From this we can conclude that temperature is related to the movement of the particles that make up bodies (this applies to solid, liquid, and gaseous bodies).
The movement of particles in gases (Fig. 12) is random (since molecules and atoms in gases practically do not interact).
Rice. 12. Movement of particles in gases
The movement of particles in liquids (Fig. 13) is “jump-like”, that is, the molecules lead a “sedentary lifestyle”, but are able to “jump” from one place to another. This determines the fluidity of liquids.
Rice. 13. Movement of particles in liquids
Particle movement in solids(Fig. 14) is called oscillatory.
Rice. 14. Movement of particles in solids
Thus, all particles are in continuous motion. This movement of particles is called thermal movement(disorderly, chaotic movement). This movement never stops (as long as the body has temperature). The presence of thermal movement was confirmed in 1827 by the English botanist Robert Brown (Fig. 15), after whom this movement is called Brownian motion.
Rice. 15. Robert Brown (1773-1858)
Today it is known that the most low temperature, which can be achieved is approximately . It is at this temperature that the movement of particles stops (however, the movement inside the particles themselves does not stop).
Galileo's experiment was described earlier, and in conclusion, let's consider another experiment - the experience of the French scientist Guillaume Amonton (Fig. 15), who in 1702 invented the so-called gas thermometer. With minor changes, this thermometer has survived to this day.
Rice. 15. Guillaume Amonton (1663-1705)
Amonton's experience
Rice. 16. Amonton's experience
Take a flask with water and plug it with a stopper with a thin tube. If you now heat the water, then due to the expansion of the water its level in the tube will increase. Based on the level of water rise in the tube, we can conclude that the temperature is changing. Advantage Amonton thermometer is that it does not depend on atmospheric pressure.
In this lesson we looked at such an important physical quantity, How temperature. We studied ways to measure it, characteristics and properties. In future lessons we will study the concept internal energy.
References
Homework
1. No. 1-4 (paragraph 1). Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
2. Why can’t Galileo’s thermoscope be calibrated?
3. An iron nail was heated on a stove:
How did the speed of movement of iron molecules change?
How will the speed of molecular movement change if a nail is placed in cold water?
How will the speed of movement of water molecules change?
How does the volume of the nail change during these experiments?
4. balloon moved from the room to the cold:
How will the volume of the ball change?
How will the speed of air molecules inside the ball change?
How will the speed of the molecules inside the ball change if it is returned to the room and, in addition, placed next to the battery?
Events physical world are inextricably linked to temperature changes. Every person gets to know her early childhood when he realizes that the ice is cold and the boiling water burns. At the same time, it becomes clear that processes of temperature change do not occur instantly. Later, at school, the student learns that this is connected with thermal movement. And a whole section of physics is dedicated to processes related to temperature.
This scientific concept introduced to replace ordinary terms. IN everyday life Words such as hot, cold or warm appear constantly. They all talk about the degree of heating of the body. This is exactly how it is defined in physics, only with the addition that it is a scalar quantity. After all, temperature has no direction, but only a numerical value.
IN international system units (SI) temperature is measured in degrees Celsius (ºC). But in many formulas describing thermal phenomena, it is required to convert it to Kelvin (K). There is a simple formula for this: T = t + 273. In it, T is the temperature in Kelvin, and t is in Celsius. Associated with the Kelvin scale is the concept of absolute zero temperature.
There are several other temperature scales. In Europe and America, for example, Fahrenheit (F) is used. Therefore, they must be able to be written in Celsius. To do this, subtract 32 from the readings in F, then divide it by 1.8.
Its explanation requires knowledge of concepts such as temperature and thermal motion. And this experiment is easy to perform.
It will require three containers. They should be large enough to easily fit your hands. Fill them with water different temperatures. In the first it should be very cold. In the second - heated. Pour into the third hot water, one in which it will be possible to hold your hand.
Now the experience itself. Lower left hand in a container with cold water, right - with the hottest. Wait a couple of minutes. Take them out and immediately immerse them in a container of warm water.
The result will be unexpected. The left hand will feel like the water is warm, the right hand will feel cold water. This is due to the fact that thermal equilibrium is first established with the liquids in which the hands are initially immersed. And then this balance is suddenly disrupted.
It describes all thermal phenomena. And these statements are quite simple. Therefore, when talking about thermal motion, it is necessary to know these provisions.
First: substances are formed by tiny particles located at some distance from each other. Moreover, these particles can be both molecules and atoms. And the distance between them is many times more sizes particles.
Second: in all substances there is thermal movement of molecules, which never stops. The particles move randomly (chaotically).
Third: particles interact with each other. This action is due to the forces of attraction and repulsion. Their magnitude depends on the distance between particles.
Proof that bodies consist of particles with gaps between them is their So, when a body is heated, its size increases. This happens due to the particles moving away from each other.
Another confirmation of this is diffusion. That is, the penetration of molecules of one substance between particles of another. Moreover, this movement turns out to be mutual. Diffusion proceeds faster the further the molecules are located from each other. Therefore, mutual penetration will occur much faster in gases than in liquids. But in solids, diffusion takes years.
By the way, the latter process also explains thermal motion. After all, the mutual penetration of substances into each other occurs without any outside intervention. But it can be accelerated by heating the body.
A clear proof that thermal motion exists is Brownian motion of particles. It is considered for suspended particles, that is, for those that are significantly larger than the molecules of the substance. These particles can be dust particles or grains. And they should be placed in water or gas.
The reason for the random movement of a suspended particle is that molecules act on it from all sides. Their action is random. The magnitude of the impacts is different at each point in time. Therefore, the resulting force is directed in one direction or the other.
If we talk about the speed of thermal movement of molecules, then there is a special name for it - root mean square. It can be calculated using the formula:
v = √[(3kT)/m 0 ].
In it, T is the temperature in Kelvin, m 0 is the mass of one molecule, k is Boltzmann’s constant (k = 1.38*10 -23 J/K).
Particles attract and repel. In explaining many processes associated with thermal motion, this knowledge turns out to be important.
After all, the forces of interaction depend on the state of aggregation of the substance. Thus, gases practically do not have them, since the particles are removed so much that their effect does not manifest themselves. In liquids and solids they are noticeable and ensure the preservation of the volume of the substance. In the latter, they also guarantee maintenance of shape.
Proof of the existence of attractive and repulsive forces is the appearance of elastic forces during deformation of bodies. Thus, with elongation, the forces of attraction between molecules increase, and with compression, the forces of repulsion increase. But in both cases they return the body to its original shape.
(pV)/N = (2E)/3.
In this formula, p is pressure, V is volume, N is the number of molecules, E is average kinetic energy.
On the other hand, this equation can be written as follows:
If we combine them, we get the following equality:
From it follows the following formula for the average kinetic energy of molecules:
This shows that energy is proportional to the temperature of the substance. That is, as the latter increases, the particles move faster. This is the essence of thermal movement, which exists as long as there is a temperature different from absolute zero.
This lesson examines the concept of thermal motion and such a physical quantity as temperature.
Thermal phenomena are of great importance in human life. We encounter them both during weather forecasts and when boiling ordinary water. Thermal phenomena are associated with such processes as the creation of new materials, the melting of metals, the combustion of fuel, the creation of new types of fuel for cars and aircraft, etc.
Temperature is one of the most important concepts associated with thermal phenomena, since often it is temperature that is the most important characteristic of the occurrence of thermal processes.
Definition.Thermal phenomena- these are phenomena associated with heating or cooling of bodies, as well as with changes in their state of aggregation (Fig. 1).
Rice. 1. Ice melting, water heating and evaporation
All thermal phenomena are associated with temperature.
All bodies are characterized by the state of their thermal equilibrium. The main characteristic of thermal equilibrium is temperature.
Definition.Temperature- this is a measure of the “warmth” of the body.
Since temperature is a physical quantity, it can and should be measured. To measure temperature, a device called thermometer(from Greek thermo- "warm", metreo- “measuring”) (Fig. 2).
Rice. 2. Thermometer
The first thermometer (or rather, its analogue) was invented by Galileo Galilei (Fig. 3).
Rice. 3. Galileo Galilei (1564-1642)
Galileo's invention, which he presented to his students at university lectures at the end of the 16th century (1597), was called thermoscope. The operation of any thermometer is based on the following principle: physical properties of a substance change depending on temperature.
Galileo's experiment was as follows: he took a flask with a long stem and filled it with water. Then he took a glass of water and turned the flask upside down, placing it in the glass. Some of the water naturally poured out, but as a result a certain level of water remained in the leg. If you now heat the flask (which contains air), the water level will drop, and if you cool it, then, on the contrary, it will rise. This is due to the fact that when heated, substances (in particular, air) tend to expand, and when cooled, they tend to contract (this is why the rails are not continuous, and the wires between the posts sometimes sag a little).
Rice. 4. Galileo's experiment
This idea formed the basis of the first thermoscope (Fig. 5), which made it possible to evaluate temperature changes (it is impossible to accurately measure temperature with such a thermoscope, since its readings will greatly depend on atmospheric pressure).
Rice. 5. Copy of Galileo's thermoscope
At the same time, the so-called degree scale was introduced. The word itself degree translated from Latin means “step”.
To date, three main scales have been preserved.
1. Celsius
The most widely used scale is one that everyone has known since childhood - the Celsius scale.
Anders Celsius (Fig. 6) is a Swedish astronomer who proposed the following temperature scale: - boiling point of water; - freezing temperature of water. Nowadays we are all accustomed to the inverted Celsius scale.
Rice. 6 Andres Celsius (1701-1744)
Note: Celsius himself said that this choice of scale was caused by a simple fact: but in winter there will be no negative temperature.
2. Fahrenheit scale
In England, the USA, France, Latin America and some other countries, the Fahrenheit scale is popular.
Gabriel Fahrenheit (Fig. 7) is a German researcher and engineer who first used his own scale for making glass. The Fahrenheit scale is more subtle: in terms of dimension, a degree on the Fahrenheit scale is smaller than a degree on the Celsius scale.
Rice. 7 Gabriel Fahrenheit (1686-1736)
3. Reaumur scale
The technical scale was invented by the French researcher R.A. Reaumur (Fig. 8). According to this scale, it corresponds to the freezing temperature of water, but Reaumur chose a temperature of 80 degrees as the boiling point of water.
Rice. 8. René Antoine Reaumur (1683-1757)
In physics, the so-called absolute scale - Kelvin scale(Fig. 8). 1 degree Celsius is equal to 1 degree Kelvin, but the temperature in corresponds approximately (Fig. 9).
Rice. 9. William Thomson (Lord Kelvin) (1824-1907)
Rice. 10. Temperature scales
Let us recall that when the temperature of a body changes, its linear dimensions change (when heated, the body expands, when cooled, it contracts). This is due to the behavior of molecules. When heated, the speed of movement of particles increases; accordingly, they begin to interact more often and the volume increases (Fig. 11).
Rice. 11. Changing linear dimensions
From this we can conclude that temperature is related to the movement of the particles that make up bodies (this applies to solid, liquid, and gaseous bodies).
The movement of particles in gases (Fig. 12) is random (since molecules and atoms in gases practically do not interact).
Rice. 12. Movement of particles in gases
The movement of particles in liquids (Fig. 13) is “jump-like”, that is, the molecules lead a “sedentary lifestyle”, but are able to “jump” from one place to another. This determines the fluidity of liquids.
Rice. 13. Movement of particles in liquids
The movement of particles in solids (Fig. 14) is called oscillatory.
Rice. 14. Movement of particles in solids
Thus, all particles are in continuous motion. This movement of particles is called thermal movement(disorderly, chaotic movement). This movement never stops (as long as the body has temperature). The presence of thermal movement was confirmed in 1827 by the English botanist Robert Brown (Fig. 15), after whom this movement is called Brownian motion.
Rice. 15. Robert Brown (1773-1858)
Today it is known that the lowest temperature that can be achieved is approximately . It is at this temperature that the movement of particles stops (however, the movement inside the particles themselves does not stop).
Galileo's experiment was described earlier, and in conclusion, let's consider another experiment - the experience of the French scientist Guillaume Amonton (Fig. 15), who in 1702 invented the so-called gas thermometer. With minor changes, this thermometer has survived to this day.
Rice. 15. Guillaume Amonton (1663-1705)
Amonton's experience
Rice. 16. Amonton's experience
Take a flask with water and plug it with a stopper with a thin tube. If you now heat the water, then due to the expansion of the water its level in the tube will increase. Based on the level of water rise in the tube, we can conclude that the temperature is changing. Advantage Amonton thermometer is that it does not depend on atmospheric pressure.
In this lesson we looked at such an important physical quantity as temperature. We studied ways to measure it, characteristics and properties. In future lessons we will study the concept internal energy.
References
Homework
1. No. 1-4 (paragraph 1). Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
2. Why can’t Galileo’s thermoscope be calibrated?
3. An iron nail was heated on a stove:
How did the speed of movement of iron molecules change?
How will the speed of molecular movement change if a nail is placed in cold water?
How will the speed of movement of water molecules change?
How does the volume of the nail change during these experiments?
4. The balloon was moved from the room to the cold:
How will the volume of the ball change?
How will the speed of air molecules inside the ball change?
How will the speed of the molecules inside the ball change if it is returned to the room and, in addition, placed next to the battery?
Any substance consists of tiny particles - molecules. Molecule- is the smallest particle of a given substance that retains all of it chemical properties. Molecules are located discretely in space, i.e. at certain distances from each other, and are in a state of continuous disorderly (chaotic) movement .
Since bodies are made up of large number molecules and the movement of molecules is random, it is impossible to say exactly how many blows one or another molecule will experience from others. Therefore, they say that the position of the molecule and its speed at each moment of time are random. However, this does not mean that the movement of molecules does not obey certain laws. In particular, although the speeds of molecules at some point in time are different, most of them have speed values close to some specific value. Usually, when speaking about the speed of movement of molecules, they mean average speed (v$cp).
It is impossible to single out any specific direction in which all molecules move. The movement of molecules never stops. We can say that it is continuous. Such continuous chaotic movement of atoms and molecules is called -. This name is determined by the fact that the speed of movement of molecules depends on body temperature. The more average speed movement of body molecules, the higher its temperature. Conversely, the higher the body temperature, the greater the average speed of molecular movement.
The movement of liquid molecules was discovered by observing Brownian motion - the movement of very small particles of solid matter suspended in it. Each particle continuously makes abrupt movements in arbitrary directions, describing trajectories in the form of a broken line. This behavior of particles can be explained by considering that they experience impacts from liquid molecules simultaneously with different sides. The difference in the number of these impacts from opposite directions leads to the movement of the particle, since its mass is commensurate with the masses of the molecules themselves. The movement of such particles was first discovered in 1827 by the English botanist Brown, observing particles under a microscope pollen in the water, which is why it was named - Brownian motion.
