My sister likes playing table tennis very much. Once, I played table tennis with her and accidentally knocked it to the ground. I was just about to pick it up. My 3-year-old brother waddled by and stepped on the table tennis impartially. The ping-pong ball was squashed. "This is the only table tennis in the family. You hit the table tennis to the ground, so buy it! " My sister said, "I'm not. If you say so, my brother should buy it. " I argued. At this time, the frugal grandmother came out of the room and asked us, "What's the matter? What are you arguing about? " So, I told my grandmother everything, but she smiled and said, "No need to buy it. I'll tell you a good way to restore table tennis! " "Then, grandma asked me to pour a pot of boiling water. I was really "not enough" at that time. What medicine does grandma sell in the gourd? I have no choice but to do as grandma says. Then, grandma put the table tennis in boiling water, and something magical happened: the table tennis actually recovered slowly! What is the reason? Grandma said it was "expansion due to heat and contraction due to cold", but I still didn't understand it, so I asked my parents and consulted many books about "expansion due to heat and contraction due to cold" before I understood the mystery. It turns out that the situation of qi is relatively simple. For gases, the molecular potential energy can be ignored and only the kinetic energy of molecules can be considered. With the increase of temperature, the average kinetic energy of gas molecules increases, and after the average kinetic energy of molecules increases, the collision of molecules becomes more intense. For the container, that is to say, the pressure of the gas will increase. If the pressure is not changed, the volume can only be increased to offset the violent collision caused by the temperature rise. For liquid and solid, both kinetic energy and potential energy of molecules must be considered, and the average kinetic energy of liquid molecules will increase with the increase of temperature. According to the equipartition theorem of energy, in a thermodynamic equilibrium system, the energy of each degree of freedom should be equally divided, and at the same time, the potential energy should be increased, so it is necessary to increase the distance between molecules to increase the potential energy, that is, expand with heat and contract with cold. However, the potential energy should be increased.
There are many trivial things in life. As long as we observe and find out carefully, there are still big secrets in it.
Write a short article about the principle of table tennis "expansion with heat and contraction with cold". Everyone may be familiar with it, but what is its principle? I'm afraid few people know * * *? I just found out a few days ago.
Next, I'll tell you how I know the principle of "thermal expansion and cold contraction".
My sister likes playing table tennis very much. Once, I played table tennis with her and accidentally knocked it to the ground. I'm going to get it. My 3-year-old brother waddled by, stepped on the table tennis impartially and was crushed.
"There is only one table tennis at home. You hit it on the ground. You buy it! " Sister said.
"I don't want it, as you say, it should be bought by my brother.
"I argued.
At this time, my thrifty grandmother came out of the room and asked us, "What's the matter? What are you arguing about? " So, I told my grandmother everything, but she smiled and said, "No need to buy it. I'll tell you a good way to restore table tennis! " "Then, grandma asked me to pour a pot of boiling water. I was really "not enough" at that time. What medicine does grandma sell in the gourd? I have no choice but to do what grandma says.
Then, grandma put the table tennis in boiling water, and something magical happened: the table tennis actually recovered slowly! What is the reason? Grandma said it was "expansion due to heat and contraction due to cold", but I still didn't understand it, so I asked my parents and consulted many books about "expansion due to heat and contraction due to cold" before I understood the mystery. It turns out that the situation of qi is relatively simple. For gases, the molecular potential energy can be ignored and only the kinetic energy of molecules can be considered. With the increase of temperature, the average kinetic energy of gas molecules increases, and after the average kinetic energy of molecules increases, the collision of molecules becomes more intense. For containers,
For liquids and solids, both kinetic energy and potential energy of molecules must be considered, and the average kinetic energy of liquids will increase with the increase of temperature. According to the equipartition theorem of energy, in a thermodynamic equilibrium system, the energy of each degree of freedom should be equally divided, and at the same time the potential energy should be increased, so it is necessary to increase the distance between molecules to increase the potential energy, that is, expand with heat and contract with cold.
However, there are also special cases of "thermal expansion and cold contraction". For example, in the process of four degrees Celsius to zero degrees Celsius, the colder the water, the larger the volume.
There are many trivial things in life. As long as we observe and find out carefully, there are still big secrets in it. ...
I know what it means to expand with heat and contract with cold. My mother cooked the eggs and asked me to look: one was soaked in cold water for a while and the other was put in a bowl.
I asked my mother, "What are you doing?" Mother said, "We will do an experiment today to know what expansion with heat is and contraction with cold.
"I applaud.
I put the eggs on the table, and my mother peeled them off for me first. I knocked on the tables and peeled them off happily.
But it is difficult to peel, and the peeled eggshell still contains a lot of albumin.
My mother peeled me eggs soaked in cold water again. I peeled it three times and twice, and the peeled eggs were smooth and white. I said to my mother, "This egg is really easy to peel. Why? " Mother said, "Think about it first. If we usually fill the kettle too full when boiling water, what will happen after the water boils? " I said, "Of course the water will come out.
"My mother praised me and said," How clever! Correct answer! " "Want to know why?" Mom teased me.
I nodded in agreement.
My mother told me, "Because the water gets bigger when heated, it comes out." .
Many objects will increase in volume when heated and decrease in volume when cooled, which is called thermal expansion and cold contraction.
When a hot egg is put into cold water, both the eggshell and protein will shrink, but protein will shrink more than the eggshell, so that the eggshell and protein will leave, so peeling is easy and protein will not be absorbed.
I finally understand the truth that the principle of thermal expansion and cold contraction is really amazing! ...
One night, I was helping my mother cook dinner. My mother asked me to unscrew the newly bought soy sauce bottle, but I couldn't.
I asked my mother, "Mom, why can't the soy sauce bottle be unscrewed?" Can you help me unscrew it? "Mom said," use your brain, I won't help you twist it.
"... start the science around me. One night, I was cooking dinner for my mother. My mother asked me to unscrew the newly bought soy sauce bottle, but I couldn't.
I asked my mother, "Mom, why can't the soy sauce bottle be unscrewed?" Can you help me unscrew it? "Mom said," use your brain, I won't help you twist it.
I said angrily, "Mom, why don't you unscrew it for me?" Mother said, "If you think again, I won't tell you.
"I can only think.
I thought it should belong to science.
So, I began to turn over the science books I had studied unhappily.
Suddenly, I turned to the lesson that heat expands and cold contracts. My heart is sweeter than eating honey and happier than getting 100.
I said to myself, "let me try this expansion and contraction!" " It's no use watching you swell with heat and shrink with cold. Today, let's try your technique of expanding with heat and contracting with cold.
"Speak, just try it in the kitchen.
Put some hot water first, soak the soy sauce bottle in hot water for five minutes, and then rinse it with cold water. It's easy to unscrew.
I think: Is there so much scientific knowledge hidden in human life? Is this scientific knowledge just waiting for us to dig? After this incident, I sincerely thank science. It helps me to make progress and grow.
bale
Ask for a scientific paper. It's better to be about thermal expansion and cold contraction.
Punch a hole in the thin iron sheet with a nail, so that the nail can move back and forth freely and take it down.
Then clamp the nail with pliers and heat it on the fire. After the nail burns red, take the nail and penetrate the small hole in the iron plate. You will find that your nails can't get through, which means your nails are getting thicker. If you don't heat the nail on the fire, but freeze it on the ice for a while, then the nail will easily go through the hole because it is thinner than before.
Through experiments, you should never underestimate the thermal expansion and cold contraction of solids, because the shape of solids is fixed and the density is much greater than that of gases and liquids, so its power of thermal expansion and cold contraction is also the greatest.
If we don't pay attention to the expansion and contraction of solids, disaster will happen.
In practice, we should take active measures to prevent it.
For example, the rails on the railway are made in sections, and when they are laid, there are certain gaps at the joints.
With these gaps, when the rail expands when heated, there is room for expansion, which keeps the rail straight and ensures driving safety.
If the rails are closely connected one by one, leaving no gaps, they will bend and deform after being heated and expanded in summer, so it is very unsafe for trains to run on them, and even accidents will occur.
So, how big is the expansion of the rails? We can do a simple calculation.
According to the measurement, every time the rail temperature rises by 65438 0℃, its length will be extended by one hundred thousandth, that is to say, every time the rail temperature rises by 65438 0℃, its length will be increased by 65438 0 cm.
If the highest temperature of the rail is 35℃ in hot summer and minus 20℃ in cold winter, the temperature difference of the rail is 55℃ in a year. In this case, the rail extension range of100km is 55m.
Look, don't leave any gaps! In fact, leaving a gap not only ensures safety, but also saves the rails, which can be described as killing two birds with one stone.
If you observe carefully at ordinary times, you will also find that in some large buildings and equipment with large temperature changes, the problem of thermal expansion and cold contraction is considered.
For example, a building often has two or three expansion joints; A bridge is always fixed at one end and supported on rollers at the other end, so the bridge can expand and contract freely when the temperature changes; There are always some U-tubes on the steam pipes in the factory. When pipes are stretched or shrunk by heat, they will only change the bending degree of U-shaped pipes, but will not affect other parts. ...
There are many experiments in my mind about the experiment of thermal expansion and cold contraction, but the one that impressed me the most is the experiment of thermal expansion and cold contraction.
In a science class in grade three, Mr. Xiao appeared at the door of the classroom with steady steps, hey! So much experimental equipment! A small bracket with a ring, a small iron ball with a handle, an alcohol lamp and a glass of cold water.
We are all confused and don't know what's going on.
Just then, Mr. Xiao put the bracket on the podium, then put the iron ball with the handle in the small circle of the bracket and "carried" it back. I feel bored. Suddenly, Mr. Xiao lit the alcohol lamp and cooked the iron ball by hand on the outer flame of the alcohol lamp. When the iron ball was "baked" slightly red, Mr. Xiao took it out. Imagine, Xiao.
This time, however, the iron ball seemed to be possessed, just didn't want to get into the circle. Teacher Xiao took out the iron ball again, put it in cold water with a "zi", and there was a burst of white smoke in the cup. Then put it in the circle, the magic seems to have disappeared, and the iron ball went in. While we were in the fog, Mr. Xiao said with a smile. This is a world full of miracles. Only one temperature can change the volume of an object! There must be many unknown secrets in this world waiting for us to discover. I hope I can become an outstanding scientist in the future and make contributions to every planet and every living thing in the universe.
...
Junior high school composition: Know what heat expands and cold contracts. My mother cooked the eggs and asked me to see them: one was soaked in cold water for a while, and the other was put in a bowl.
I asked my mother, "What are you doing?" Mother said, "We will do an experiment today to know what expansion with heat is and contraction with cold.
"I applaud.
I put the eggs on the table, and my mother peeled them off for me first. I knocked on the tables and peeled them off happily.
But it is difficult to peel, and the peeled eggshell still contains a lot of albumin.
My mother peeled me eggs soaked in cold water again. I peeled it three times and twice, and the peeled eggs were smooth and white. I said to my mother, "This egg is really easy to peel. Why? " Mother said, "Think about it first. If we usually fill the kettle too full when boiling water, what will happen after the water boils? " I said, "Of course the water will come out.
"My mother praised me and said," How clever! Correct answer! " "Want to know why?" Mom teased me.
I nodded in agreement.
My mother told me, "Because the water gets bigger when heated, it comes out." .
Many objects will increase in volume when heated and decrease in volume when cooled, which is called thermal expansion and cold contraction.
When a hot egg is put into cold water, both the eggshell and protein will shrink, but protein will shrink more than the eggshell, so that the eggshell and protein will leave, so peeling is easy and protein will not be absorbed.
I finally understand the truth that the principle of thermal expansion and cold contraction is really amazing! ...
A composition that can change 90 words must be 90 words. Everyone may encounter such a problem in life-it is an interesting phenomenon to accidentally step on table tennis and throw it away.
Never throw it! Table tennis can still be bulged.
It's actually quite simple.
Prepare a pot of hot water, preferably about 90 degrees, and then put the flat table tennis into the hot water to see if the table tennis has recovered. See if it is still alive. Is it as good as new? Someone asked what this principle is, and there are only two words-hot rise.
Because the air in the ball will expand when heated, like an invisible hand to "support" the flat place.
Maybe someone asks: Why not use cold water? Let's do another experiment.
You also need to use a flat table tennis ball, prepare a pot of cold water, and then put the flat table tennis ball into the cold water to see if it bulges. If you look carefully, you will find that table tennis has become smaller.
This is a brother who expands with heat and contracts with cold.
Its principle is just the opposite of thermal expansion: air will condense when it is cold, and then it will become slightly smaller, and the object will also become smaller.
Of course, the interesting phenomenon of thermal expansion and cold contraction can not only make table tennis expand and contract, but also have great power if it is combined with cold and heat! For example, if someone is trapped in a cave sealed by a big stone and can't get out, he only needs to burn the stone very hot with a torch first, and then pour cold water on it, and the stone will automatically crack and be completely shattered after repeated times.
Look, this is an interesting phenomenon in nature. As long as you try to explore, you will find more phenomena! I hope I can help you and adopt it.
My Discovery Composition 600 words In life, we will make many discoveries, and I am no exception.
In my memory, there is a discovery that I will never forget.
This is a much colder winter than before. After school, my mother told me with a sad face that her favorite cup was broken.
I only sighed and ignored my mother, but seeing her face developing in the direction of "eggplant", I quickly asked, "What's the matter?" "I was going to pour a glass of water in the morning. Unexpectedly, the cup exploded as soon as the water was poured into it.
"Mom's face is a little better.
I was surprised: "What's the reason?" My flattering temper has come up again. I went into the computer room with a "whew" and looked up information on the Internet. "oh! It turned out that it was caused by' expansion with heat and contraction with cold'! It is also said on the Internet that the reason why wires hang loosely between two telephone poles is also because of' thermal expansion and cold contraction'. If the wires between telephone poles are pulled tightly, the wires will break as soon as they contract when it is cold in winter ... "I saw a message on the Internet," If you say so, expansion with heat and contraction with cold are really troublesome guys! Isn't it more convenient to eliminate it from life? " I muttered to myself.
A few days later, I subscribed to We Love Science. I saw my favorite Magic Loki and His Students in it. Ye Yuxin, the protagonist, also encountered the same problem as her mother-the cup exploded when pouring water, and it was about the knowledge of thermal expansion and cold contraction. I suddenly remembered the whimsy of the other day and was eager to find the answer, so I continued reading, but what I said was quite contrary to my idea. According to the book, if there is no "heat expansion and cold contraction", winter will be miserable-even if the heating is turned on to the maximum, it will not feel warm, but it will get colder and colder, because the hot water in the heating pipe will not only transfer heat to the radiator, but also to the air around the radiator, and the air will naturally flow to the top of the room when heated and expanded.
The cold air in the room will soon flow to fill this position.
It is the constant convection of hot and cold air that makes the room warm.
If there is no "expansion with heat and contraction with cold", hot air cannot expand with heat, and cold and warm air cannot convection. Even if the radiator is hot again, the room is not warm.
It is also said that if there is no "thermal expansion and cold contraction", the gas stove will not catch fire, because the air can't convection and can't take away the burning carbon dioxide, so the fire won't catch fire.
At the end of the book, it is also said that water generally expands with heat and contracts with cold, but it contracts with heat and expands with cold at a certain temperature, which is between 4 and 0 degrees Celsius, that is, the lower the temperature, the larger the volume.
When water freezes, its volume will be larger than the original liquid, so water pipes often burst in cold winter.
Unexpectedly, this day really can't go on without "expansion with heat and contraction with cold".
It is worthwhile to break a cup and gain so much knowledge!
I didn't expect a 600-word composition. It was crisp in autumn.
I came to the supermarket to buy some school supplies, and I was very happy.
After my careful selection, I finally chose my school supplies.
I took my school supplies and went to the cashier to pay.
At this point, people who pay at the cashier have lined up.
I waited carefully in the back, but my eyes rolled aimlessly. Suddenly, my eyes lit up: an old woman's 10 yuan fell to the ground and the team was moving. People are passing by 10 yuan. Suddenly, a handsome guy with a top-grade MP4 business mobile phone and a brand-name handbag bent down and threw his mobile phone on the ground.
I thought my uncle would pick up the money and return it to my grandmother, but "everyone knows his face, but he doesn't know his heart." My uncle put the money into his pocket without anyone knowing. Although others saw the "good thing" that my uncle did, no one turned a blind eye. I didn't like what my uncle did, so I went up to him with a smile and said, "Uncle, please give her back the 10 yuan my grandmother gave her!" Hearing this, my uncle paused and said to me, "What money?" "Is the money you picked up in front.
"I replied and shouted," Grandma, your money ... "Before I finished, my uncle gave me a heavy push. I stumbled and almost fell down, so I had to lower my head and dare not speak.
Grandma saw it and ignored me. Instead, she scolded me indiscriminately: "You are crazy!" I'm sorry to hear the news.
What a surprise: Uncle Kuo will be greedy 10 yuan's cheap? Why did I help my grandmother, but she was "a dog bit Lv Dongbin ―― she doesn't know how to love people"? Why didn't anyone accuse my uncle? Has everyone forgotten the spirit of changing money? Everyone behind grandma passed by 10 yuan, but no one saw it or told grandma? I cried that day.
Although the sky is clear as blue, my mood is very bad. It is cloudy and rainy.
Thermal expansion and cold contraction [1] is a basic property of an object. In general, an object will expand when heated and contract when cold.
All objects have this property.
(Note: Water will expand when heated above 4 degrees Celsius, and contract when cooled below 4 degrees Celsius.
Objects expand when heated and contract when cooled.
This is because the motion of particles (atoms) in an object changes with temperature. When the temperature rises, the vibration amplitude of particles increases, which makes the object expand. However, when the temperature drops, the vibration amplitude of particles will decrease, thus causing the object to contract.
Everything expands with heat and contracts with cold. We can use this phenomenon to solve some difficulties in our daily life.
Students observe the experiment 1 observe the volume change of copper balls when they are heated and cooled; Description of animation: The main body of the animation is a copper ball suspended by a thin thread, and the animation background is an iron ring, an alcohol lamp and a pot of cold water.
First, students choose a metal ring just enough to cover the copper ball to determine the size of the copper ball, then heat the copper ball on an alcohol lamp, pass through the metal ring, and then cool it in cold water, and then determine the volume change of the copper ball when it is hot or cold through the metal ring.
In experiment 2, a balloon was used to cover the bottle mouth, and the volume change of the balloon was observed when the bottle was heated and cooled.
Description: The main body of the animation is an air bottle with a balloon in its mouth, and the background of the animation is two containers filled with cold water and hot water respectively.
Students first put the air bottle in a hot water vessel to observe the volume change of the balloon, and then put it in a cold water vessel to observe the volume change of the balloon.
3. Report the observation results and form an explanation (1). Through the experiment of 1, it is concluded that copper has the property of thermal expansion and cold contraction, and it is inferred that solids have the property of thermal expansion and cold contraction.
(2) Through Experiment 2, it is concluded that air expands with heat and contracts with cold, and it is inferred that all gases expand with heat and contract with cold.
4. Self-inductance (1) Problem: Liquid (water) has the property of expanding with heat and contracting with cold, as do gas (air) and solid (copper). Can you express this attribute in one sentence? (2) It is concluded that general objects expand when heated and contract when cooled.
5. Application migration (1) Teacher's question: Thinking 1 Why does the flat table tennis recover after being scalded by hot water? Thinking 2 Why is there a gap between the rails? Think about the wire between two telephone poles. Why is it so tight in winter? Thinking 4: Why can't bicycle tires be inflated too much in summer? (2) Analysis and reference: These four thinking questions are all introduced from daily life cases, so as to understand the essence of objects expanding with heat and contracting with cold, which conforms to children's cognitive characteristics and enables students to apply what they have learned to real life and deepen their learning impression.
For the presentation of these four questions, video clips are used to show them, so that the questions can be clearly presented to students.
At the same time, the teacher also gives reference answers for students to think about. The reference answers in reference 1 and reference 3 not only explain the reasons theoretically, but also give the actual figures. For example, if the temperature of the gas rises 1℃, the volume of the gas will expand 1/273, and the wire per 100 meter will stretch about 1℃ when the temperature rises.
In the reference answer of Thinking 2, the historical facts of laying the first railway track in Britain in 1825 are listed to warn students not to follow the laws of nature and make them more interested in learning.
Most substances in nature follow the law of "expansion with heat and contraction with cold", with few exceptions.
Water is an exception.
The density of water is the highest at 4 degrees, and below 4 degrees is abnormal expansion, which is "thermal contraction and cold expansion".
Speaking of ice, the density is only 0.9.
This means that ice will float on the water.
In addition, there is: the metal that contracts and expands with cold-antimony is a silver-gray metal. It always has four "children", and people see it the most often. Its name is "Grey Antimony".
It also has three little "younger brothers", yellow antimony, black antimony and explosive antimony.
However, the chemical "personality" of these three little brothers is unstable.
Antimony likes low temperature. As soon as the temperature exceeds MINUS 80 degrees Celsius, it can't live, so it becomes black antimony.
As long as black antimony is heated, it will become ordinary gray antimony.
As for the explosion of antimony, it is even worse. As long as you touch it with a hard object, you will "fly into a rage" and release a lot of heat, which will soon become gray antimony.
Antimony has an abnormal state-thermal contraction and cold expansion.
As we all know, general objects expand when heated and contract when cooled. However, when liquid antimony cools and solidifies, its volume becomes larger.
In the past, people used this strange temper of antimony to make movable type.
Some liquid antimony is added to the molten lead alloy. However, when the mixed melt is poured into a copper mold for cooling and solidification, the volume of the solid lead alloy will increase a little, so that every tiny stroke will be clearly highlighted.
In addition, the addition of antimony can make lead alloy harder and more wear-resistant.
Please indicate the source for reprinting. I know what a 400-word composition is when it expands with heat and contracts with cold.