Various kinds of things happen in the world around us. physical phenomena, which 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 of bodies. 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 various directions, can collide both with each other and with the walls of the vessel. 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, its various properties. 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 from a liquid, turn into solid.
T 
body temperature directly depends on the average kinetic energy 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.
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Goals.
- Educational.
- Give the concept of temperature as a measure of average kinetic energy; consider the history of the creation of thermometers, compare different temperature scales; develop the ability to apply acquired knowledge to solve problems and perform practical tasks, expand students' horizons in the field of thermal phenomena.
- Educational.
- Developing the ability to listen to your interlocutor and express your own point of view
- Developmental.
- Development in students of voluntary attention, thinking (the ability to analyze, compare, build analogies, draw conclusions.), cognitive interest (based on a physical experiment);
- formation of ideological concepts about the knowability of the world.
DURING THE CLASSES
Hello, please sit down.
When studying mechanics, we were interested in the movement of bodies. Now we will consider phenomena associated with changes in the properties of bodies at rest. We will study heating and cooling of air, melting of ice, melting of metals, boiling of water, etc. Such phenomena are called thermal phenomena.
We know that when cold water is heated, it first becomes warm and then hot. The metal part removed from the flame gradually cools. The air surrounding the batteries hot water, heats up, etc.
We use the words “cold”, “warm”, “hot” to denote the thermal state of bodies. The quantity characterizing the thermal state of bodies is temperature.
Everyone knows that the temperature of hot water is higher than the temperature of cold water. In winter, the outside air temperature is lower than in summer.
All molecules of any substance move continuously and randomly (chaotically).
The random chaotic movement of molecules is called thermal motion.
Tell me, what is the difference between thermal motion and mechanical motion?
It involves many particles with different trajectories. The movement never stops. (Example: Brownian motion)
Demonstration of the Brownian motion model
What does thermal motion depend on?
- Experiment No. 1: Dip a piece of sugar in cold water, and the other is hot. Which one will dissolve faster?
- Experiment No. 2: Place 2 pieces of sugar (one larger than the other) in cold water. Which one will dissolve faster?
The question of what temperature is turned out to be very difficult. How, for example, does hot water differ from cold water? For a long time there was no clear answer to this question. Today we know that at any temperature water consists of the same molecules. Then what exactly changes in water as its temperature increases? From experience we saw that sugar will dissolve much faster in hot water. Dissolution occurs due to diffusion. Thus, Diffusion occurs faster at higher temperatures than at lower temperatures.
But the cause of diffusion is the movement of molecules. This means that there is a connection between the speed of movement of molecules and body temperature: in the body with higher temperature molecules move faster.
But temperature depends not only on the average speed of molecules. For example, oxygen, the average speed of molecules of which is 440 m/s, has a temperature of 20 °C, and nitrogen, with the same average speed of molecules, has a temperature of 16 °C. The lower temperature of nitrogen is due to the fact that nitrogen molecules are lighter than oxygen molecules. Thus, the temperature of a substance is determined not only by the average speed of movement of its molecules, but also by their mass. We see the same in experiment No. 2.
We know quantities that depend on both the speed and the mass of the particle. This is impulse and kinetic energy. Scientists have found that it is the kinetic energy of molecules that determines body temperature: temperature is a measure of the average kinetic energy of particles in a body; the greater this energy, the higher the body temperature.
So, when bodies heat up, the average kinetic energy of molecules increases, and they begin to move faster; When cooled, the energy of the molecules decreases and they begin to move more slowly.
Temperature is a quantity that characterizes the thermal state of the body. A measure of the “heat” of a body. The higher the temperature of a body, the greater the average energy of its atoms and molecules.
Is it possible to rely only on your sensations to judge the degree of heating of the body?
- Experiment No. 1: Touch a wooden object with one hand and a metal object with the other.
Compare the sensations
Although both objects are at the same temperature, one hand will feel cold and the other warm
- Experiment No. 2: take three vessels with hot, warm and cold water. Place one hand in a vessel with cold water and the other in a vessel with hot water. After some time, place both hands in a vessel with warm water
Compare the sensations
The hand that was in hot water now feels cold, and the hand that was in cold water now feels warm, although both hands are in the same vessel.
We have proven that our feelings are subjective. Instruments are needed to confirm them.
Instruments used to measure temperature are called thermometers. The action of such a thermometer is based on the thermal expansion of a substance. When heated, the column of the substance used in the thermometer (for example, mercury or alcohol) increases, and when cooled it decreases. The first liquid thermometer was invented in 1631 by the French physicist J. Rey.
The body temperature will change until it comes into thermal equilibrium with the environment.
The law of thermal equilibrium: for any group of isolated bodies, after some time the temperatures become the same, i.e. a state of thermal equilibrium occurs.
It should be remembered that any thermometer always shows its own temperature. To determine the temperature of the environment, the thermometer should be placed in this environment and wait until the temperature of the device stops changing, taking a value equal to the ambient temperature. When the temperature of the environment changes, the temperature of the thermometer will also change.
A medical thermometer designed to measure human body temperature operates somewhat differently. It belongs to the so-called maximum thermometers, recording the highest temperature to which they were heated. Having measured your own temperature, you may notice that, when you find yourself in a colder environment (compared to the human body), the medical thermometer continues to show the same value. To return the mercury column to its original state, this thermometer must be shaken.
With a laboratory thermometer used to measure the temperature of the environment, this is not necessary.
Thermometers used in everyday life allow you to express the temperature of a substance in degrees Celsius (°C).
A. Celsius (1701-1744) - Swedish scientist who proposed the use of a centigrade temperature scale. On the Celsius temperature scale beyond zero (s mid-18th century c.) the temperature of melting ice is taken, and 100 degrees is the boiling temperature of water at normal atmospheric pressure.
Let's listen to a message about the history of the development of thermometers (Presentation by Sidorova E.)
Liquid thermometers are based on the principle of changing the volume of liquid that is poured into the thermometer (usually alcohol or mercury) when the ambient temperature changes. Disadvantage: different liquids expand differently, so thermometer readings vary: Mercury -50 0 C; glycerin -47.6 0 C
We tried to make a liquid thermometer at home. Let's see what comes of it. (Video by Brykina V. Appendix 1)
We learned that there are different temperature scales. In addition to the Celsius scale, the Kelvin scale is widely used. The concept of absolute temperature was introduced by W. Thomson (Kelvin). The absolute temperature scale is called the Kelvin scale or thermodynamic temperature scale.
The unit of absolute temperature is kelvin (K).
Absolute zero is the lowest possible temperature at which nothing can be colder and theoretically impossible to extract from a substance thermal energy, the temperature at which the thermal movement of molecules stops
Absolute zero is defined as 0 K, which is approximately 273.15 °C
One Kelvin is equal to one degree T=t+273
Questions from the Unified State Exam
Which of the following options for measuring hot water temperature using a thermometer gives the most correct result?
1) The thermometer is immersed in water and, after removing it from the water after a few minutes, the readings are taken
2) The thermometer is lowered into the water and waited until the temperature stops changing. After this, without removing the thermometer from the water, take its readings
3) The thermometer is lowered into the water and, without removing it from the water, the readings are immediately taken
4) The thermometer is lowered into the water, then quickly removed from the water and the readings are taken
The figure shows part of the scale of a thermometer hanging outside the window. The air temperature outside is
- 18 0 C
- 14 0 C
- 21 0 C
- 22 0 C
Solve problems No. 915, 916 (“Collection of problems in physics 7-9” by V.I. Lukashik, E.V. Ivanova)
- Homework: Paragraph 28
- No. 128 D “Collection of problems in physics 7-9” V.I.Lukashik, E.V. Ivanova
Methodological support
- “Physics 8” S.V. Gromov, N.A. Motherland
- “Collection of problems in physics 7-9” V.I. Lukashik, E.V.
- Ivanova
Drawings that are publicly available on the Internet
To study the topic “Thermal Movement” we need to repeat:
In the world around us, various kinds of physical phenomena occur that are directly related to changes in body temperature.
Since childhood, we remember that the water in the lake is first cold, then barely warm, and only after a while it becomes suitable for swimming
With such words as “cold”, “hot”, “slightly warm”, we define different degrees of “heating” of bodies, or, in the language of physics, different temperatures of bodies. If you compare the temperature in the lake in summer and late autumn, the difference is obvious.
The temperature of warm water is slightly higher than the temperature of ice water.
As is known, diffusion occurs faster at higher temperatures. It follows from this that the speed of movement of molecules and temperature are deeply interrelated.
Conduct an experiment: Take three glasses and fill them with cold, warm and hot water, and now put a tea bag in each glass and observe how the color of the water changes? Where will this change occur most intensely? 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.
If you increase the temperature, the speed of movement of molecules will increase, if you decrease it, it will decrease. Thus, we conclude:
Phenomena that relate to heating or cooling of bodies and temperature changes are called thermal. These include heating or cooling not only liquid bodies, but also gaseous and solid air.
Molecules, or atoms, which are the basis of all bodies, are in endless chaotic motion. The movement of molecules in different bodies happens in different ways. Gas molecules move randomly at high speeds along a very complex trajectory.When they collide, they bounce off each other, changing the magnitude and direction of the velocities.
Liquid molecules oscillate around equilibrium positions (since they are located almost close to each other) and relatively rarely jump from one equilibrium position to another. The movement of molecules in liquids is less free than in gases, but more free than in solids.
In solids, molecules and atoms vibrate around certain average positions.
As the temperature increases, the particle speed increases, That's why The chaotic movement of particles is usually called thermal.
Interesting:
What is the exact height of the Eiffel Tower? And this depends on the ambient temperature!
The fact is that the height of the tower varies by as much as 12 centimeters.
and the temperature of the beams can reach up to 40 degrees Celsius.
And as you know, substances can expand under the influence of high temperature.
Chaoticity is the most important feature of thermal motion. One of the most important evidence of the movement of molecules 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). Brownian movement was discovered by the English botanist Robert Brown (1773-1858).
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.
Let's remember how the properties of water change with temperature changes.
Body temperature directly depends on the average kinetic energy of 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.
Temperature - a quantity that characterizes the thermal state of the body or, in other words, a measure of the “heating” of the body.
The higher the temperature of a body, the greater the average energy of its atoms and molecules.
Temperature is measured thermometers, i.e. temperature measuring instruments
Temperature is not directly measured! The measured value is temperature dependent!
Currently, there are liquid and electric thermometers.
In modern liquid thermometers, this is the volume of alcohol or mercury. The thermometer measures your own temperature! And, if we want to measure the temperature of some other body using a thermometer, we must wait some time until the temperatures of the body and the thermometer are equal, i.e. thermal equilibrium will occur between the thermometer and the body. The home thermometer “thermometer” needs time to give more precisely the meaning the patient's temperature.
This is the law of thermal equilibrium:
For any group of isolated bodies, after some time the temperatures become the same,
those. a state of thermal equilibrium occurs.
Body temperature is measured using a thermometer and is most often expressed in degrees Celsius(°C). There are also other units of measurement: Fahrenheit, Kelvin and Reaumur.
Most often, physicists measure temperature on the Kelvin scale. 0 degrees Celsius = 273 degrees Kelvin
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The thermal movement of molecules of substances in a liquid state is similar to their movement for substances in crystalline and gaseous states. In crystals, the thermal motion of molecules is expressed mainly in vibrations of molecules relative to equilibrium positions, which practically do not change over time. The thermal motion of molecules in gases is mainly their translational movement and rotation, the directions of which change in collisions.
The thermal movement of molecules of a substance on the surface of a substrate is called migration. During migration, it becomes possible for molecules to collide - two or less often three - with each other. Colliding molecules come together under the influence of van der Waals forces. So, doublets and triplets are formed. They are more difficult to desorb than single molecules, since their bonds with the surface are noticeably stronger. These formations are active centers during the condensation of subsequent settling molecules.
Since the thermal movement of the molecules of a body substance disrupts their ordered arrangement, magnetization decreases with increasing temperature.
Since the thermal movement of the molecules of a body substance disrupts their ordered arrangement, magnetization decreases with increasing temperature. If this body is removed from the external field, then the chaotic movement of the molecules will lead to its complete demagnetization.
Pressure saturated vapors created by the thermal movement of molecules of a substance in the vapor phase at a certain temperature.
The gaseous state occurs when the energy of thermal motion of the molecules of a substance exceeds the energy of their interaction. The molecules of the substance in this state acquire a rectilinear forward motion, A individual properties substances are lost, and they obey the laws common to all gases. Gaseous bodies do not have their own shape and easily change their volume when exposed to external forces or when temperature changes.
Absolute zero (0 K) is characterized by the cessation of thermal movement of the molecules of a substance and corresponds to a temperature below 0 C by 273 16 C.
Kinetic theory matter allows us to establish a connection between pressure and the kinetic energy of thermal motion of the molecules of a substance.
If the internal movements in molecules are connected with their external thermal movement, then it is impossible to understand the properties of a substance, its chemical behavior, without studying this connection, without taking into account those factors that affect the thermal movement of the molecules of a substance (temperature, pressure, environment, etc. ) and through this thermal movement also influence the state internal movement in every single molecule.
Thus, it was found that any substance can be converted from a gaseous state to a liquid state. However, each substance can experience such a transformation only at temperatures below a certain, so-called critical temperature Tc. Above the critical temperature, the substance does not turn into a liquid or solid at any pressure. It is obvious that at a critical temperature the average kinetic energy of thermal motion of the molecules of a substance exceeds the potential energy of their binding in a liquid or solid. Since the attractive forces acting between the molecules of different substances are different, the potential energy of their connection is also different, hence the values of the critical temperature for different substances are also different.
Relaxation times 1 and T2 are introduced above as constants, which must be determined from experience. The values of 7 measured for various substances lie in a wide range from K) 4 sec for solutions of paramagnetic salts to several. Experienced data indicates close connection values of relaxation times with the structure and nature of thermal motion of the molecules of the substance.
The absolute temperature T, K, characterizes the degree of heating of the body. In particular, the melting point of ice (0 C) and the boiling point of water (100 C) at normal atmospheric pressure were taken as the initial values used in the construction of the International Practical Celsius Temperature Scale to establish the origin of temperature and its unit of measurement - degrees. Temperatures above 0 C are considered positive, and temperatures below 0 C are considered negative. In the SI system of units, temperature calculations are made from absolute zero in degrees of the Kelvin thermodynamic scale. The absolute zero of this scale (0 K) is characterized by the cessation of thermal movement of the molecules of a substance and corresponds on the Celsius scale to a temperature of - 273 15 C. Thus, both scales differ only in the starting point, and the division price (degree) is the same for them.
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The term "temperature" appeared at a time when physicists thought that warm bodies consisted of more specific substance - caloric - than the same bodies, but cold. And temperature was interpreted as a value corresponding to the amount of caloric in the body. Since then, the temperature of any body has been measured in degrees. But in fact it is a measure of the kinetic energy of moving molecules, and, based on this, it should be measured in Joules, in accordance with the System of Units C.
The concept of “absolute zero temperature” comes from the second law of thermodynamics. According to it, the process of heat transfer from a cold body to a hot one is impossible. This concept was introduced by the English physicist W. Thomson. For his achievements in physics, he was given the title of nobility “Lord” and the title “Baron Kelvin”. In 1848, W. Thomson (Kelvin) proposed using a temperature scale in which starting point took absolute zero temperature, corresponding to extreme cold, and at the cost of division took a degree Celsius. The Kelvin unit is 1/27316 of the temperature of the triple point of water (about 0 degrees C), i.e. temperature at which pure water is immediately found in three forms: ice, liquid water and steam temperature is the lowest possible low temperature at which the movement of molecules stops and it is no longer possible to extract thermal energy from a substance. Since then the scale absolute temperatures began to be called by his name.
Temperature is measured on different scales
The most commonly used temperature scale is called the Celsius scale. It is based on two points: the temperature of the phase transition of water from liquid to steam and water to ice. A. Celsius in 1742 proposed the distance between reference points divide into 100 intervals, and take the water as zero, with the freezing point as 100 degrees. But the Swede K. Linnaeus suggested doing the opposite. Since then, water has frozen at zero degrees A. Celsius. Although it should boil exactly at Celsius. Absolute zero Celsius corresponds to minus 273.16 degrees Celsius.
There are several more temperature scales: Fahrenheit, Reaumur, Rankin, Newton, Roemer. They have different division prices. For example, the Reaumur scale is also built on the reference points of boiling and freezing of water, but it has 80 divisions. The Fahrenheit scale, which appeared in 1724, is used in everyday life only in some countries of the world, including the USA; one is the temperature of the mixture of water ice and ammonia and the other is the temperature of the human body. The scale is divided into one hundred divisions. Zero Celsius corresponds to 32 Conversion of degrees to Fahrenheit can be done using the formula: F = 1.8 C + 32. Reverse conversion: C = (F - 32)/1.8, where: F - degrees Fahrenheit, C - degrees Celsius. If you are too lazy to count, go to an online service for converting Celsius to Fahrenheit. In the box, enter the number of degrees Celsius, click "Calculate", select "Fahrenheit" and click "Start". The result will appear immediately.
Named after the English (more precisely Scottish) physicist William J. Rankin, former contemporary Kelvin and one of the creators of technical thermodynamics. On his scale important points three: the beginning is absolute zero, the freezing point of water is 491.67 degrees Rankine and the boiling point of water is 671.67 degrees. The number of divisions between the freezing of water and its boiling for both Rankine and Fahrenheit is 180.
Most of these scales are used exclusively by physicists. And 40% of American high school students surveyed today said that they do not know what absolute zero temperature is.
