Option 1. Equipment: A test tube with water and an alcohol lamp.

To demonstrate the poor thermal conductivity of the liquid, water is poured into the test tube ¾ of the volume. Holding the test tube in your hands at a slight angle above the flame of the spirit lamp, heat the water at the open end (Fig. 130). They show that the water here boils quickly, but at the bottom there is no great heating.

Rice. 130 Fig. 2.105 Fig. 131

Experience 4. Thermal conductivity of gases

Option 1. Equipment: two test tubes, two stoppers, two rods, two balls, a spirit lamp, a tripod, a hanger.

Poor thermal conductivity of air is demonstrated using two identical tubes closed with stoppers through which short rods are passed. Steel balls are attached to the ends of the rods with plasticine or paraffin (Fig. 131). The test tubes above the alcohol lamp are arranged so that convection occurs in one of them, and the thermal conductivity of air occurs in the other. It is noticed that in one test tube the ball quickly falls away from the rod.

Option 2. See fig. 2.105

Experience 5. Convection of liquids

Option 1. Equipment: a device for demonstrating the convection of a liquid, potassium permanganate, a spirit lamp, a tripod.

The device, which is a closed glass tube (Fig. 132), is fixed in the leg of the tripod. (It is better to hang the tube than to clamp it at the bottom, for in the latter case the glass is more likely to break.) Fill the tube with water through the upper opening of any elbow so that there are no air bubbles along the entire closed path inside the tube.

When performing the experiment, potassium permanganate crystals are placed in a spoon with a grid and lowered into the knee (you can simultaneously lower two spoons with potassium permanganate crystals into both knees). Then a spirit lamp is brought to the lower part of this knee and convection is observed.

Rice. 132 Fig. 133

Experience 6. Convection of gases

Option 1. Equipment: spirit lamp, matches, paper snake, metal point.

To demonstrate gas convection, a paper snake is made, which rotates in a stream of ascending hot air coming from a spirit stove or electric stove (Fig. 133). (When installing the snake on the point, do not pierce the paper.)

Experience 7. Heating by radiation

Option 1. Equipment: heat sink, open demonstration pressure gauge, table lamp (or electric stove).

The heat sink, connected by a tube to a demonstration manometer (see Fig. 123), is fixed in a tripod opposite the radiator. As a radiating body, you can take an electric stove, a vessel with hot water, etc. A heat sink is brought to it from the side with the dark side and the readings of the pressure gauge are observed for 1-2 minutes.

Then the heat sink is turned with a shiny surface to the lamp located at the same distance from the heat sink, and during the same time the reading of the pressure gauge is monitored. They make a conclusion.

In the second series of experiments, the lamp incandescence (or the distance to the emitter) is reduced and the change in the pressure gauge readings is again observed under the same conditions. They make a conclusion.

Option 2. See Fig. 2.99; 2.101.

Question. In which case a change in the readings of a liquid manometer

Is it faster if the heat transfer and heat sink face each other with shiny surfaces or if they face each other with black surfaces?

Rice. 123 Fig. 2.101 Fig. 2.99

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• Participant:Sharoglazova Ksenia Sergeevna
• Head: Pecherskaya Svetlana Yurievna

The purpose of this work: the study of the phenomenon of thermal conductivity, having done a series of experiments with solids, liquids and gases.

Relevance: Nowadays, new materials are being developed. Knowledge of the thermal conductivity of various substances makes it possible not only to widely use them, but also to prevent their harmful effects in everyday life, technology and nature.

Target: the study of the phenomenon of thermal conductivity, having done a series of experiments with solids, liquids and gases.

Tasks:

• to study the theoretical material on this issue;
• investigate the thermal conductivity of solids;
• investigate the thermal conductivity of liquids;
• investigate the thermal conductivity of gases;
• draw conclusions about the results.

Hypothesis: all substances (solid, liquid and gaseous) have different thermal conductivity.

Equipment: spirit lamp, tripod, wooden stick, glass stick, copper wire, test tube with water.

Elements of the teaching materials for the textbook by A.V. Peryshkin: textbook "Physics. Grade 8 "A.V. Peryshkina

Internal energy, like any kind of energy, can be transferred from one body to another. Internal energy can also be transferred from one part of the body to another. So, for example, if one end of a nail is heated in a flame, then its other end, which is in the hand, will gradually heat up and burn the hand. The phenomenon of transfer of internal energy from one part of the body to another or from one body to another when they are in direct contact is called thermal conductivity.

Let us study this phenomenon by doing a series of experiments with solids, liquids and gases.

Video: https://cloud.mail.ru/public/JCFY/CFTcCeqhE

. Investigation of the thermal conductivity of solids on the example of a wooden stick, a glass rod and a copper rod

Let's bring the end of a wooden stick into the fire. It will ignite.

Conclusion: wood has poor thermal conductivity.

We bring the end of a thin glass rod to the flame of an alcohol lamp. After a while, it will heat up, while the other end will remain cold.

Conclusion: glass has poor thermal conductivity.

If we heat the end of a metal rod in a flame, then very soon the entire rod will become very hot. We can no longer hold it in our hands.

Conclusion: metals conduct heat well, that is, they have a high thermal conductivity. Silver and copper have the highest thermal conductivity.

Consider the transfer of heat from one part of a solid body to another in the following experiment. We fix one end of a thick copper wire in a tripod. Attach a few carnations to the wire with wax (Fig. 6). When the free end of the wire is heated in the flame of an alcohol lamp, the wax will melt. The cloves will gradually fall off. First, those that are closer to the flame will disappear, then all the rest in turn.

Let's find out how energy is transferred along the wire. The speed of the oscillatory movement of metal particles increases in that part of the wire that is closer to the flame. Since particles constantly interact with each other, the speed of movement of neighboring particles increases. The temperature of the next part of the wire begins to rise, and so on. It should be remembered that during heat conduction, there is no transfer of matter from one end of the body to the other.

Experience 2. Study of the thermal conductivity of liquids using water as an example

Consider now the thermal conductivity of liquids. Take a test tube with water and begin to heat its upper part. The water at the surface will soon boil, and at the bottom of the test tube, during this time, it will only heat up (Fig. 7). This means that liquids have low thermal conductivity, with the exception of mercury and molten metals. This is due to the fact that in liquids the molecules are located at greater distances from each other than in solids.

Conclusion: the thermal conductivity of liquids is less than the thermal conductivity of metals.

Experience 3. Study of the thermal conductivity of gases

We investigate the thermal conductivity of gases.

We put a dry test tube on a finger and heat it in the flame of an alcohol lamp with the bottom up (Fig. 8). The finger will not feel warm for a long time. This is due to the fact that the distance between gas molecules is even greater than that of liquids and solids.

Conclusion: The thermal conductivity of gases is even lower than that of liquids. So, the thermal conductivity of different substances is different.

Conclusions and discussion

Conclusion: The experiments carried out show that the thermal conductivity of various substances is different. Metals have the highest thermal conductivity, liquids have low thermal conductivity, and gases have the lowest thermal conductivity.

Using §4 of the physics textbook for grade 8, we present the results in the form of a table:

Explanation of the phenomenon of heat conduction from a molecular kinetic point of view: thermal conductivity is the transfer of energy from one part of the body to another, which occurs when molecules or other particles interact. In metals, the particles are close, they constantly interact with each other. The speed of oscillatory motion in the heated part of the metal increases and is quickly transferred to neighboring particles. The temperature of the next part of the wire rises. In liquids and gases, molecules are located at greater distances than in metals. In a space where there are no particles, heat conduction cannot take place.

Application of thermal conductivity

Thermal conductivity in the kitchen

Thermal conductivity and its regulation are important in the process of cooking. Often, during the heat treatment of the product, it is necessary to maintain a high temperature, therefore, metals (copper, aluminum ...) are used in the kitchen, as their thermal conductivity and strength are higher than those of other materials. Pots, pans, baking sheets, and other utensils are made of metal. When they come into contact with a heat source, this heat is easily transferred to the food. Sometimes it is necessary to reduce the thermal conductivity - in this case, use pans made of materials with a lower thermal conductivity, or cook in ways that transfer less heat to the food. Cooking food in a water bath is one example of a decrease in thermal conductivity. For dishes intended for cooking, materials with high thermal conductivity are not always used. In an oven, for example, ceramic dishes are often used, the thermal conductivity of which is much lower than that of metal dishes. Their most important advantage is the ability to keep the temperature. A good example of the use of materials with high thermal conductivity in the kitchen is the stove. For example, electric stove burners are made of metal to ensure good heat transfer from the hot coil of the heating element to the pot or pan. People use materials with low thermal conductivity between hands and utensils to avoid getting burned. The handles of many pots are made of plastic, and the trays are removed from the oven with oven mitts made of cloth or plastic with low thermal conductivity.

Materials with low thermal conductivity are also used to maintain the temperature of food unchanged. So, for example, to keep morning coffee or soup, which is taken on a trip or for lunch at work, remained hot, it is poured into a thermos, cup or jar with good thermal insulation. Most often, food remains hot (or cold) in them due to the fact that between their walls there is a material that conducts heat poorly. It can be foam or air, which is in a closed space between the walls of the vessel. It does not allow heat to pass into the environment, food to cool, and hands to get burned. Styrofoam is also used for cups and takeaway food containers. In a vacuum Dewar (known as a "thermos", after the brand name), there is almost no air between the outer and inner wall - this further reduces thermal conductivity.

Heating system

The task of any heating system is the efficient transfer of energy from the coolant (hot water) to the room. To do this, use special elements of the heating system - radiators. Radiators are designed to increase the heat transfer of the thermal energy accumulated in the system to the room. They are a sectional or monolithic structure, inside which the coolant circulates. The main characteristics of a heating radiator: material of manufacture, type of construction, overall dimensions (number of sections), heat transfer. The higher this indicator, the less heat loss will be during the transfer of energy from the coolant to the room. The best material for making radiators is copper. The most commonly used cast iron radiators; aluminum radiators; steel radiators; bimetallic radiators.

Thermal conductivity for heat

We use materials with low thermal conductivity to maintain a constant body temperature. Examples of such materials are wool, down, and synthetic wool. The skin of animals is covered with fur, and birds are covered with down with low thermal conductivity, and we borrow these materials from animals or create synthetic fabrics similar to them, and make clothes and shoes from them that protect us from the cold. In addition, we make blankets, as it is more comfortable to sleep under them than in clothes. Air has a low thermal conductivity, but the problem with cold air is that it is usually free to move in any direction. It displaces the warm air around us, and we get cold. If the movement of air is limited, for example, by enclosing it between the outer and inner walls of the vessel, then it provides good thermal insulation. Snow and ice also have low thermal conductivity, so people, animals and plants use them for thermal insulation. In fresh, unpacked snow, there is air inside, which further reduces its thermal conductivity, especially since the thermal conductivity of air is lower than that of snow. Thanks to these properties, ice and snow cover protects plants from freezing. Animals dig holes and entire caves for wintering in the snow. Travelers passing through snow-covered areas sometimes dig such caves to spend the night in them. Since ancient times, people have been building ice shelters, and now they are creating entire entertainment centers and hotels. Fires often burn in them, and people sleep in furs and synthetic sleeping bags.

To ensure normal life in the body of people and animals, it is necessary to maintain a certain temperature within very narrow limits. Blood and other fluids, as well as tissues, have different thermal conductivity and can be adjusted depending on the needs and ambient temperature. So, for example, the body can change the amount of blood in a part of the body or throughout the body by dilating or constricting blood vessels. Our body can also thicken and thin the blood. At the same time, the thermal conductivity of the blood, and, consequently, of the part of the body where this blood flows, changes.

Heat therapy

Modern methods of heat treatment can be divided into three large groups: 1) contact application of heated media; 2) light-thermal irradiation; and 3) the use of heat generated in tissues during the passage of high-frequency electric current. Let us dwell on the use of heated media. For heat treatment, media are selected that allow creating a significant supply of heat in them. This warmth must then be slowly and gradually transferred to the body throughout the procedure. To do this, the medium must possibly have a high heat capacity and relatively low thermal conductivity and convection capacity. The following media are mainly used for heat treatment: air, water, peat, therapeutic mud and paraffin.

Thermal conductivity in the bath

Many people like to relax in saunas or baths, but it would be impossible to sit there on benches made of a material with high thermal conductivity. It takes a long time to equalize the temperature of such materials with body temperature, so materials with low thermal conductivity are used instead, such as wood, the upper layers of which take on body temperature much faster. Since the temperature in the sauna gets quite high, people often wear hats made of wool or felt to protect their heads from the heat. In Turkish hammam baths, the temperature is much lower, so they use a material with a higher thermal conductivity - stone - for benches.

Is it warm for prickly animals in needles?

Wool not only saves animals from the cold, but also serves as a means of protection. And to make the protection more impressive and reliable, the hairline sometimes changes, turning into a kind of armor. Needles, for example. But does such a vestment retain the properties inherent in wool, do hedgehogs and porcupines in their prickly fur coats get chilly?

Scientists of the Institute of Problems of Ecology and Evolution. A.N. Severov, Russian Academy of Sciences, thoroughly studied the heat-conducting and heat-insulating properties of needles taken from the back of an adult male North American porcupine from the collection of the Zoological Museum of Moscow State University, and made sure that these same needles heat very well. To understand the internal structure of the needles, thin sections were made on them, on which gold was deposited for examination in an electron microscope. Keratin - the main component of the needles - conducts heat 10 times better than air. And thanks to this, the needles increase the thermal conductivity of the “armor”. Consequently, heat loss from the animal's body also increases. However, the internal porous structure of the needles creates additional shielding of thermal radiation, which, most likely, compensates for the increase in thermal conductivity. So the porcupine, like other prickly animals, does not suffer from the cold at all. The spiny cover retains just as much heat as a warm-blooded animal of this size needs.

Polypropylene

So far, it is the best basis for materials (fibers, threads, yarn, fabrics, fabrics) used in the production of underwear sportswear, thermal underwear and thermal socks. Among all synthetic materials used in this area, it has the lowest thermal conductivity. Therefore, clothing made of polypropylene is the best way to keep warm in winter and cool in summer.

Which material has the highest thermal conductivity?

The material with the highest thermal conductivity is not at all any metal (silver or copper), as many people think. The highest thermal conductivity has a material that looks like glass - diamond. Its thermal conductivity is almost 6 times greater than that of silver or copper. If you make a teaspoon of diamond, then you will not be able to use it, as it will burn your fingers in the same second.

What are piles made of when constructing buildings in regions with permafrost?

Great difficulties for the builders of buildings are delivered by the subsidence of the foundation, especially in regions with permafrost. Houses often give cracks due to thawing of the soil under them. The foundation transfers some amount of heat to the soil. Therefore, buildings began to be built on piles. In this case, heat is transferred only by thermal conductivity from the foundation to the pile and further from the pile to the ground. What should piles be made of? It turns out that the piles, made of durable solid material, must be filled with kerosene inside. In summer, the pile conducts heat from top to bottom poorly, because. liquid has low thermal conductivity. In winter, due to the convection of the liquid inside the pile, on the contrary, it will contribute to additional cooling of the soil.

"Fireball"

An ordinary balloon, inflated with air, ignites easily in a candle flame. He immediately bursts. If, however, the same ball filled with water is brought to the flame of a candle, it becomes “refractory”. The thermal conductivity of water is 24 times greater than that of air. This means that water conducts heat 24 times faster than air. Until the water evaporates inside the balloon, it will not burst.

Korobitsyn Denis

Thermal conductivity of various materials with increasing heating temperature.

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INTRODUCTION

One day, I asked my mother why she always gives us wooden spoons when we sit down to eat. She replied that wooden ones heat up more slowly than iron ones and you won’t burn yourself with them. I thought, because I noticed that metal objects heat up very quickly, but why? It turned out that all solid materials have such a property, called thermal conductivity. I was wondering which materials conduct heat faster and which ones slower, and what happens if you increase the heating temperature, will these materials heat up in the same order?

Hypothesis: I think that different materials have different thermal conductivity and that as the heating temperature increases, they will heat up in the same order.

Object: thermal conductivity.

Subject: thermal conductivity of some materials.

Purpose: To determine why different objects heat up differently, despite the fact that they were heated under the same conditions, but were made of different materials.

Tasks:

1) study the literature and Internet materials on the issue of thermal conductivity of materials;

2) conduct an experiment in order to determine the thermal conductivity of materials;

3) introduce classmates to the topic studied.

To implement these tasks and confirm the hypothesis:

1. Select scientific literatureon the issue of thermal conductivity of materials;
2. I will study this literature and draw conclusions;
3. To confirm the theoretical conclusions, I will conduct an experiment;
4. Based on the results of the experiment, I will draw conclusions;
5. I will acquaint classmates with the results of these conclusions.

II MAIN PART

2.1 What is thermal conductivity?

The main source of heat on Earth is the Sun. But, in addition, people use many artificial sources of heat: a fire, a stove, water heating, gas and electric heaters, etc.

It was not immediately possible to answer the question of what heat is. Only in the 18th century did it become clear that all bodies are made up of molecules, that molecules move and interact with each other. Then scientists realized that heat is related to the speed of movement of molecules. When bodies are heated, the speed of molecules increases, and when cooled, it decreases.

You know that if you dip a cold spoon into hot tea, after a while it will heat up. It is clear from the example that heat can be transferred from a hotter body to a cooler body.

Thermal conductivity- the transfer of energy from more heated parts of the body to less heated ones, as a result of thermal motion and interaction of particles.

Wool, hair, bird feathers, paper, cork and other porous bodies have poor thermal conductivity. This is due to the fact that air is contained between the fibers of these substances. Vacuum (space freed from air) has the lowest thermal conductivity.

1. Snow is a porous, loose substance, it contains air. Therefore, snow has poor thermal conductivity and well protects the earth, winter crops, fruit trees from freezing.

2. Kitchen potholders are made of a material that has poor thermal conductivity. Handles of teapots, pans are made of materials with poor thermal conductivity. All this protects hands from burns when touching hot objects.

3. Substances with good thermal conductivity (metals) are used to quickly heat bodies or parts.

2.1 Conducting the experiment

For the experiment, I needed: a glass bowl, a wooden, metal and plastic spoon, a glass tube, plasticine, chips, margarine, a stopwatch, a sheet for recording results and a pen.

Having prepared all the necessary materials, I began to conduct the experiment. I set the spoons and glass tube vertically in the bowl and attached them with plasticine to the sides of the bowl. Then, using identical cubes of margarine, I attached the chips to each item. Then he filled the bowl with warm water and turned on the stopwatch. I expected to make an experiment with warm water, and then with boiling water.

After 10 minutes had passed, and not one chip had moved, I decided that the water temperature was not enough to melt the margarine.

I drained the warm water and carefully poured boiling water, turned on the stopwatch. Next, I wrote down the sequence in which the chips slid off the objects:

metal spoon - 52 seconds;

glass tube - 4 minutes 13 seconds;

plastic spoon - 5 minutes 7 seconds;

wooden spoon - 6 minutes 18 seconds.

I want to add that when the chip slipped off the metal spoon, after two minutes I added more boiling water, because the margarine did not melt under the rest of the chips.

Thus, I found out that metal is the best conductor of heat, and wooden objects conduct heat worse than all the selected materials. This means that metal has a high thermal conductivity, it heats up quickly and cools down quickly, while wood, on the contrary, has a low thermal conductivity, heats up slowly and cools down slowly. Also, I noticed that a metal spoon heated up in less than a minute, other objects heated up much longer, which means that metal conducts heat very quickly, unlike plastic, glass and wood.

III CONCLUSION

Thus, as a result of the work done, I found out that thermal conductivity is a property of solid materials, which allows you to evaluate how quickly a particular material heats up and cools down.

As a result of the experiment, it was found that metal objects have the highest thermal conductivity, then glass, then plastic, and wood has the lowest thermal conductivity.

The hypothesis was partially verified, since the temperature of warm water was low and the first part of the experiment could not be carried out. However, in the second part of the experiment, we confirmed the hypothesis - different materials have different thermal conductivity.

IV REFERENCES

1. A. V. Peryshkin, Textbook of physics - M .: Bustard, 2010, - pp. 11-14

2. Site materials http://class-fizika.narod.ru/8_3.htm

3. Site materials http://elementy.ru/trefil/21095

4. Site materials http://www.fizika.ru/kniga/index.ph

5. Site materials http://class-fizika.spb.ru/index.php/opit/726-op-teplpr

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I INTRODUCTION……………………………………………………………………………………..3

II MAIN PART…………………………….………………………………………………4

2.1 What is thermal conductivity ...…………………………………………………………………4

2.2. Conducting an experiment……………………………………………………………………..5

III CONCLUSION……………………………………………………………………………....6

IV LIST OF LITERATURE…………………………………………………………...………7

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Municipal Autonomous Educational Institution "Secondary School No. 8 with an in-depth study of individual subjects in the city of Nazarovo, Krasnoyarsk Territory" Thermal conductivity of materials Author: Denis Korobitsyn 4 "B" class Leader: Adolf E.Ya., primary school teacher Nazarovo 2015

Purpose: to determine why different objects heat up differently, despite the fact that they were heated under the same conditions, but were made of different materials. Hypothesis: I think different materials have different thermal conductivity and that as the heating temperature increases, they will heat up in the same order.

Tasks: 1) to study the literature and Internet materials on the issue of thermal conductivity of materials; 2) conduct an experiment to determine the thermal conductivity of materials; 3) introduce classmates to the topic studied.

In the 18th century, scientists realized that heat is related to the speed of molecules. When bodies are heated, the speed of molecules increases, and when cooled, it decreases. Heat is transferred from a hotter body to a cooler one.

Thermal conductivity is the transfer of energy from more heated parts of the body to less heated ones, as a result of thermal motion and interaction of particles.

Wool, hair, bird feathers, paper, cork and other porous bodies have poor thermal conductivity. This is due to the fact that air is contained between the fibers of these substances.

For the experiment, I needed: a glass bowl, a wooden, metal and plastic spoon, a glass tube, plasticine, chips, margarine, a stopwatch, a sheet for recording results and a pen.

The sequence of slipping chips from objects: metal spoon - 52 seconds; glass tube - 4 minutes 13 seconds; plastic spoon - 5 minutes 7 seconds; wooden spoon - 6 minutes 18 seconds.

Metal has the highest thermal conductivity, which means it heats up quickly and cools down quickly. The second thermal conductivity was glass, the third - plastics. Wood has the worst thermal conductivity, it heats up slowly and cools slowly.

The hypothesis was partially verified, since the temperature of warm water was low and the first part of the experiment could not be carried out. However, in the second part of the experiment, I confirmed the hypothesis - different materials have different thermal conductivity.

THANK YOU FOR YOUR ATTENTION!

Lesson topic:Entertaining physics lesson

on the topic "thermal phenomena"

Lesson Objectives:

1. Educational: to systematize students' knowledge on the topic "Thermal phenomena" and demonstrate to students entertaining experiments using home-made equipment.

2. Nurturing:

3. Developing: to develop logic, clarity and brevity of speech, physical terminology, generalization skills, general erudition of students.

Equipment:

Demos:

Lesson plan

Organizing time

Setting the goal of the lesson

Knowledge update

Demonstration of entertaining experiments and their explanation based on the material covered earlier

Homework

Lesson summary

During the classes

Organizing time

Setting the goal of the lesson

For several lessons, we have considered various thermal processes and learned to explain them on the basis of modern knowledge of physics.

Today in the lesson we will look at a number of entertaining experiments on this topic and explain what we observe based on the knowledge we have.

Knowledge update

But from the beginning, let's recall the material we studied earlier.

Questions:

1. What are the thermal phenomena?

   Give examples of thermal phenomena?

   What characterizes the temperature?

   How is the temperature of a body related to the speed of movement of its molecules?

   What is the difference between the movement of molecules in gases, liquids and solids?

Demonstration of entertaining experiments

Physics around us! We meet her everywhere. And what experiments can be carried out at home without using expensive instruments and equipment? Very simple and entertaining...

Experiment #1

"Focus for New Year's Eve"

This trick is best shown on New Year's Eve in a room lit only by a Christmas tree garland. The magician takes two candles from the table. He connects them with wicks, pronounces a "magic spell" - and now ... smoke appears at the point of contact of the wicks, followed by fire. The magician spreads candles to the sides - they burn! What is the secret of focus?

Answer: Those who are fond of chemistry have probably already figured out what the secret of the trick is in a self-igniting mixture. Before demonstrating the trick, prepare the props, for this you need to sprinkle the wick of one of the candles with potassium permanganate powder (potassium permanganate), and soak the other with liquid glycerin. Remember, ignition does not occur immediately, it takes some time. Be careful. The fire is real.

Experiment #2

"BOILER"

Can water boil at room temperature?

To answer this question, we will conduct the following experiment: I filled a disposable medical syringe, in which there was no needle, by 1/8 with water. Then close the hole with your finger and sharply pull the piston to its extreme position. The water inside the syringe "boiled", remaining cold. Why does water "boil"?

Answer: The boiling point depends on pressure. The lower the gas pressure above the liquid surface, the lower the boiling point of this liquid.

Experiment #3

"Can not be?"

For an experiment, boil a hard-boiled egg.
Peel it off the shell. Take a piece of paper
80 by 80 mm, roll it up like an accordion and set it on fire. Then dip the burning paper into a wide-mouthed bottle.
After 1-2 seconds, cover the neck with an egg (see figure). The burning of the paper stops, and the egg begins to be drawn into the decanter. Explain the observed phenomenon.

Answer: When the paper burns, the air inside the bottle heats up and expands. When the flame went out, the air in the bottle cooled and, accordingly, its pressure decreased, and atmospheric pressure pushed the egg into the bottle.

Comment: This experience can be made more interesting by inserting an incompletely peeled banana into the neck of the bottle. Being drawn into the bottle, he will be cleansed at the same time

Experiment #4

"Crawling Glass"

Take a clean window glass about 30 - 40 cm long. Place two matchboxes under one edge of the glass so that an inclined plane is formed. Moisten the rim of a glass of thin glass with water and place upside down on the glass. Bring a burning candle to the wall of the glass and the glass will slowly crawl. How to explain it?

Answer: This is due to the fact that when heated, the air inside the glass expands and slightly raises the glass. Water prevents air from escaping from the glass, as a result, the friction force between the glass and the glass decreases and the glass creeps down.

Experiment #5

"Observation of Evaporation and Condensation"

Experiment #6

Observe convection in cold and hot water using potassium permanganate crystals, a drop of brilliant green, or any other coloring matter as a dye. Compare the nature and speed of convection and draw conclusions

Experiment #7

It's interesting that...

The longest experiment in the history of scientific research is taking place at a university in Australia. Back in 1927, the first dean of the Faculty of Physics of this university, T. Parnell, melted some bitumen, poured it into a funnel with a stopper at the end, let it cool and settle for three years, and then took out the stopper. Since then, on average, once every 9 years, a drop of resin falls from the funnel into a glass placed below. The last drop fell at Christmas in 1999. It is believed that the funnel will be empty not earlier than in another 100 years.

PEOPLE'S WISDOM

Proverbs:

"A lot of snow - a lot of bread" Why?

Answer: Snow has poor thermal conductivity, i.e. snow is a "fur coat" for the earth, it keeps it warm. The fur coat is thick, the frost will not get to the winter crops, it will protect them from freezing.

"Without a lid, the samovar does not boil; without a mother, a child cannot frolic." Why doesn't a samovar boil for a long time without a lid?

Answer: With the lid open, some of the molecules with high kinetic energy will fly away from the surface of the water, taking energy with them.

"Frozen - as at the bottom of the sea." Why is it always cold on the seabed?

Answer: The sun's rays do not warm up the deep layers of water: thermal, infrared rays - are absorbed by almost all the water surface. In addition, water has a relatively low thermal conductivity.

Tasks - riddles

In winter it warms, in spring it smolders, in summer it dies, in autumn it flies.(Snow.)

The world warms, does not know fatigue.(The sun.)

How does the Sun's energy reach the Earth?

Answer.radiation. (by electromagnetic waves)

Hanging pear - you can not eat; do not be afraid - touch, even though there is fire inside.(Electric lamp.)

Runs without legs, burns without fire.(Electricity.)

As the Sun burns, it flies faster than the wind, the road lies in the air, it has no equal in strength.(Lightning.)

Who, without learning, speaks all languages?(Echo.)

He walks along the sea, he walks, and when he reaches the shore, he will disappear there.(Wave.)

Curls around the nose, but not in the hands.(Smell.)

Without wings, without a body, she flew a thousand miles away.(Radio wave. )

How can you carry water in a sieve?(Freezing water.)

Homework

Prepare ice in the freezer. Fold it in a plastic bag and wrap it with a downy scarf or cover it with cotton wool. Can be additionally wrapped in a fur coat. Leave this package for 5-7 hours, then check the ice. Explain the observed state.

Suggest at home a way to preserve frozen food when defrosting the refrigerator.

Lesson summary

Today in the lesson we remembered what thermal phenomena are, observed examples of thermal phenomena in experiments set up using elementary, improvised equipment and explained these phenomena.

Summing up the lesson, grading.

Internal energy, like any kind of energy, can be transferred from one body to another. Internal energy can also be transferred from one part of the body to another. So, for example, if one end of a nail is heated in a flame, then its other end, which is in the hand, will gradually heat up and burn the hand. The phenomenon of transfer of internal energy from one part of the body to another or from one body to another when they are in direct contact is called thermal conductivity.
Let us study this phenomenon by doing a series of experiments with solids, liquids and gases. Let's bring the end of a wooden stick into the fire. It will ignite. The other end of the stick, which is outside, will be cold. This means that the tree has poor thermal conductivity. We bring the end of a thin glass rod to the flame of an alcohol lamp. After a while, it will heat up, while the other end will remain cold. Consequently, glass also has poor thermal conductivity. If we heat the end of a metal rod in a flame, then very soon the entire rod will become very hot. We can no longer hold it in our hands. This means that metals conduct heat well, that is, they have a high thermal conductivity. Silver and copper have the highest thermal conductivity.
Consider the transfer of heat from one part of a solid body to another in the following experiment. We fix one end of a thick copper wire in a tripod. Attach a few carnations to the wire with wax (Fig. 6). When the free end of the wire is heated in the flame of an alcohol lamp, the wax will melt. The cloves will gradually fall off. First, those that are closer to the flame will disappear, then all the rest in turn. Let's find out how energy is transferred along the wire. The speed of the oscillatory movement of metal particles increases in that part of the wire that is closer to the flame. Since particles constantly interact with each other, the speed of movement of neighboring particles increases. The temperature of the next part of the wire begins to rise, and so on. It should be remembered that during heat conduction, there is no transfer of matter from one end of the body to the other. Consider now the thermal conductivity of liquids. Take a test tube with water and begin to heat its upper part. The water at the surface will soon boil, and at the bottom of the test tube, during this time, it will only heat up (Fig. 7). This means that liquids have low thermal conductivity, with the exception of mercury and molten metals. This is due to the fact that in liquids the molecules are located at greater distances from each other than in solids. We investigate the thermal conductivity of gases.
We put a dry test tube on a finger and heat it in the flame of an alcohol lamp with the bottom up (Fig. 8). The finger will not feel warm for a long time. This is due to the fact that the distance between gas molecules is even greater than that of liquids and solids. Therefore, the thermal conductivity of gases is even less. So, the thermal conductivity of different substances is different. The experience shown in Figure 9 shows that the thermal conductivity of different metals is not the same. Wool, hair, bird feathers, paper, cork and other porous bodies have poor thermal conductivity. This is due to the fact that air is contained between the fibers of these substances. Vacuum (space freed from air) has the lowest thermal conductivity.

This is explained by the fact that thermal conductivity is the transfer of energy from one part of the body to another, which occurs during the interaction of molecules or other particles. In a space where there are no particles, heat conduction cannot take place. If there is a need to protect the body from cooling or heating, then substances with low thermal conductivity are used. So, for pots, pans, handles are made of plastic. Houses are built from logs or bricks, which have poor thermal conductivity, which means they protect the premises from cooling.