1. Why do the stars twinkle? We see the stars shining, not because the luminosity of the stars has changed, but because of the occlusion of the atmosphere.

The atmosphere is between us and the stars. When starlight passes through the atmosphere, it will be affected by the density and thickness of the atmosphere. The atmosphere is not absolutely transparent, and its transparency will change according to its density.

So when we look at the stars through it on the ground, we will see that the stars seem to be flashing. 2. Why do people yawn? When we feel tired, a lot of carbon dioxide has been produced in our bodies.

When there is too much carbon dioxide, oxygen must be supplemented to balance the needs of the body. Because these residual carbon dioxide will affect our body's functional activities, then the body will send out a protective reaction, so we yawn.

Yawning is a deep breathing action, which will let us breathe in more oxygen and expel more carbon dioxide than usual, and it can also eliminate fatigue. 3. Why can snakes walk without feet? Snakes have many scales, which are the outermost armor on their bodies.

Scales are not only used to protect the body, but also to be their "feet". When a snake crawls forward, its body will be S-shaped.

Every scale outside the S-shape will tilt upward to help the snake catch the uneven road when it moves forward. These scales cooperate with the muscles of the snake and can push the body forward, so the snake can walk without feet! 4. Why do sunflowers always bloom towards the sun? There is a substance called "auxin" in the stem under the sunflower disk.

This substance has the function of accelerating replication, but it is anti-optical, and it will run to the backlight side whenever it encounters light. So when the sun rises, the stem of the sunflower immediately hides to the side of the backlight, as if the whole plant is bent in the direction of the sun.

5. Why does hair turn white when people are old? There is a substance called melanin in our hair. The more melanin, the darker our hair will be. Without melanin, hair will turn yellow or white.

When human beings reach old age, various functions of the body will gradually decline, and the formation of pigments will be less and less, so the hair will gradually turn white! 6. Why do fireflies glow? Fireflies emit light because there is a luminous body at the end of their abdomen, which is filled with a lot of phosphorus-containing luminescent substances and luminescent enzymes, so that fireflies can emit flashing light. The purpose of fireflies is not only lighting, but also courtship, vigilance and trapping.

This is also a communication tool for them. Different kinds of fireflies emit light in different ways, frequencies and colors, so they can convey different information. 7. Why do you growl when you are hungry? When you are hungry, you will purr. This is because the food you have eaten before has almost been digested. Although the stomach is empty, the gastric juice in the stomach will continue to secrete.

At this time, the contraction of the stomach will gradually expand, and the liquid and gas inside will be stirred up and purr. Don't be embarrassed by your stomach growling next time! Because this is a normal physiological action.

8. Why can't ostriches fly? A giant ostrich, but they can't fly into the sky! This is not because their wings are useless, but because their feathers are too soft and their wings are too small to fly at all. In addition, the ostrich's muscles are underdeveloped and its sternum is flat, which is not conducive to flying.

Ostriches live in Africa. Because they have lived in desert areas for a long time, their bodies gradually evolved into what they are now in order to adapt to the environment. 9. Why can't it go bad easily? Lunch meat, black bean shad, tomato sauce beans.

They are all delicious canned food, which can be preserved for a long time without deterioration.

This is because the can is sealed, so bacteria can't enter. When people make canned food, they pump all the air out of the canned food and then seal it.

In the absence of air, even if the food inside is contaminated with a little bacteria, they can't survive or reproduce! 10. Why does the baby cry all the time when it is born? Babies cry when they are born, not because they are unhappy, but because they are taking the first breath of air! When babies leave their mother's body and are born, the first breath of air will rush to their throats, violently impact the vocal cords, make them vibrate, and then make a sound similar to crying. 1 1. Why do lizards keep bouncing up after their tails are broken? In order to protect themselves, many lizards also protect their eyes and ears; When some lizards are attacked, their tails will be broken due to the severe contraction of their muscles.

Because there are still some nerves alive in the broken tail, it will keep bouncing, thus distracting the enemy and running away. Don't think that their lives will end like this. In fact, it only takes a few months, and their tails will grow back and move on.

12. Why is the squirrel's tail so big? Don't look at the relaxed mouse tail! When the squirrel jumps around the tree, its tail plays a great role. It can keep balance when the squirrel jumps to the tree to avoid falling and being injured.

In addition, this big tail can play a more protective role in winter, tightly surrounding the squirrel's body, which is convenient and practical. 13. Why can't a person have one or three thumbs? The average person has five fingers, each with a different length.

However, does anyone realize that besides the thumb, other fingers also have three sections, while the thumb alone has only two sections? It turns out that the number of joints is just the same as the other four fingers. If it is three knots, the thumb will appear weak, so that it can't lift heavy objects; If there is only one section, it can't grasp things freely with the other four fingers! 14. Why don't you scratch yourself? When others scratch ourselves, we will feel itchy and laugh constantly; However, when we scratch ourselves, we not only don't laugh, but also don't itch.

Based on our psychological preparation, the brain will send out a message that there is no danger, and the nerves will relax, so that they will not laugh and itch! 15. Why are most seawater blue and green? Looking at the sea, it is often found that the sea water is blue-green. However, when you pick up the sea water, you can only see it as transparent and colorless as old water.

It turns out that the sea itself is around us.

2. About 20 words of scientific and technological knowledge.

3. Why can snakes walk without feet? Can a snake walk without feet? A snake has many scales on its body, which is the outermost layer of armor. Scales are not only used to protect their bodies, but also can be their "feet". When a snake crawls forward, its body will be S-shaped. Every scale except the S-shape will be tilted to help the snake grasp the uneven road when it moves forward. These scales cooperate with the muscles of snakes and can push their bodies to crawl forward, so snakes can walk without feet! 4. Why do sunflowers always bloom towards the sun? There is a substance called "auxin" in the stem under the sunflower disk. This substance has the function of accelerating replication, but it is anti-optical, and it will run to the backlight side whenever it encounters light. So when the sun rises, the stem of sunflower will immediately hide to the side of the backlight, and it seems that the whole plant is bent towards the sun. 5. Why do people get old? When people get old, their hair will turn white. There is a substance called melanin in our hair. The more melanin, the darker the hair will be. Without melanin, hair will turn yellow or white. When human beings reach old age, various functions of the body will gradually decline, and the formation of pigments will be less and less, so the hair will gradually turn white! 6. Why do fireflies glow? Can fireflies shine? Fireflies emit light because there is a luminous body at the end of their abdomen, which is filled with a lot of phosphorus-containing luminescent substances and luminescent enzymes, so that fireflies can emit flashing light. Fireflies shine not only for lighting, but also for courtship, vigilance, trapping and other purposes. This is also a communication tool for them. Different kinds of fireflies emit light in different ways, frequencies and colors, so they can convey different information. 7. Why are they hungry? Do you growl when you are hungry? When you are hungry, you will purr. This is because the food you have eaten before has almost been digested. Although the stomach is empty, the gastric juice in the stomach will continue to secrete. At this time, the contraction of the stomach will gradually expand, and the liquid and gas inside will stir up and make a purring sound. Don't be embarrassed by the growling of your stomach next time! Because this is a normal physiological action. 8. Why can't ostriches fly? Can't ostriches fly? A giant ostrich, but they can't fly into the sky! This is not because their wings are useless, but because their feathers are too soft and their wings are too small to fly at all. In addition, the ostrich's muscles are underdeveloped and its sternum is flat, which is not conducive to flying. Ostrich has lived in Africa for a long time, and in order to adapt to the environment, its body has gradually evolved into what it is now. 9. Why can't the food in cans go bad easily? Isn't the food in cans easy to go bad? Lunch meat, black beans, tomato sauce beans.

They are all delicious canned food, which can be preserved for a long time without deterioration. This is because the can is sealed and bacteria can't get in. When people make canned food, the air inside is pumped out and then sealed. Without air, even if the food inside is stained with a little bacteria, they can't survive or reproduce! 10. Why do babies always cry at birth? Do babies always cry when they are born? Babies cry when they are born, not because they are unhappy, but because they are taking the first breath of air! When babies leave their mother's body and are born, the first breath of air will rush to their throats, violently impact the vocal cords, make them vibrate, and then make a sound similar to crying.

3. Life science tips

If the cover of a long-standing book is rolled up, it is because the humidity in the air is constantly changing; Because the paper of the book absorbs the moisture in the air, it begins to "evaporate moisture" when the air is dry, and it begins to absorb moisture when the humidity in the air is high, so it is easy to "deform" the paper fiber by constantly absorbing and evaporating moisture, so the paper will curl the lever principle.

Using the lever principle, using chopsticks not only saves labor, but also saves distance, making the operation more flexible, but it is more laborious (it doesn't matter if you spend a little effort). The strength and resistance of the lever refer to the force exerted on the lever, the strength refers to the force exerted by fingers on chopsticks, and the resistance refers to the force exerted by vegetables on chopsticks.

To determine the relationship between the force arm and the resistance arm of chopsticks, we need to find the fulcrum. The fulcrum is at the upper end of chopsticks, and the power arm is smaller than the resistance arm. Chopsticks are a laborious lever. They are all laborious levers.

Because the position of food is on the head of chopsticks. You can feel it with chopsticks.

Its fulcrum should be in the tiger's mouth (the index finger is connected with the thumb), and the strength is the force of the finger on the chopsticks, generally up and down the midpoint of the chopsticks (even if it is taken down, it can't reach the end of the chopsticks). Resistance is the force that prevents chopsticks from closing, which generally acts on the head of chopsticks.

Unless you put the dish in the middle alone, it will not be used normally. Therefore, it is a lever with less water in the power arm than in the resistance arm, and it is a laborious lever. Different people hold chopsticks in different postures, which will cause different degrees of exertion, but they are all laborious levers.

About 4.20 words of scientific knowledge. Thank you.

Small scientific knowledge

Why does sorbet get angry?

The reason why sorbet bubbles is because there is a lot of invisible water vapor in the outside air. When it comes to cold sorbet, it will liquefy into droplets when it is cold. It seems that the sorbet is bubbling.

Why do sunflowers always face the sun?

Sunflower stems contain a wonderful auxin. This auxin is very afraid of light. When it is illuminated, it will go to the backlight side, and the cells on the backlight side will multiply rapidly. Therefore, the backlit side will grow faster than the bright side, which will bend the sunflower to light.

Why does cicada shed its skin?

Cicada's shell (exoskeleton) is hard and can't expand with the growth of cicada. When the cicada grows to a certain stage, the cicada's exoskeleton restricts its growth, and the cicada loses its original exoskeleton, which is cicada slough.

5.50 Less scientific knowledge

Why do sunflowers always face the sun? Sunflower stems contain a wonderful auxin.

This auxin is very afraid of light. When it is illuminated, it will go to the backlight side, and the cells on the backlight side will multiply rapidly. Therefore, the backlit side will grow faster than the bright side, which will bend the sunflower to light.

2. Why do the stars twinkle? We see the stars shining, not because the luminosity of the stars has changed, but because of the occlusion of the atmosphere. The atmosphere is between us and the stars. When starlight passes through the atmosphere, it will be affected by the density and thickness of the atmosphere.

The atmosphere is not absolutely transparent, and its transparency will change according to its density. So when we look at the stars through it on the ground, we will see that the stars seem to be flashing.

3. Why do people yawn? When we feel tired, a lot of carbon dioxide has been produced in our bodies. When there is too much carbon dioxide, oxygen must be supplemented to balance the needs of the body.

Because these residual carbon dioxide will affect our body's functional activities, then the body will send out a protective reaction, so we yawn. Yawning is a deep breathing action, which will let us breathe in more oxygen and expel more carbon dioxide than usual, and it can also eliminate fatigue.

How high is the blue sky? "Blue sky" is actually the earth's atmosphere. The atmosphere surrounds the earth's air and is divided into five layers according to the air density, with a total thickness of 2000-3000 kilometers.

But most of the air is concentrated below 15 km from the ground, and the higher the air, the thinner it is. How thick the atmosphere is, how high the blue sky should be.

5. Why are there no stars in the daytime? Because part of the sunlight is scattered by the gas and dust in the atmosphere during the day, the sky is very bright and the light radiated by the sun is so strong that we can't see the stars. 6. What celestial bodies are there in the solar system? There are nine planets in the solar system.

They are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. In addition, there are many asteroids, comets and meteors in the solar system, and there are 2958 officially numbered asteroids.

The most famous comet is Halley's comet. 7. Why does it thunder? This is a natural phenomenon that negative electricity meets positive electricity.

When it rains, some clouds in the sky are positively charged and some are negatively charged. When two clouds meet, they will discharge, emit bright and bright lightning, and at the same time release a lot of heat, which will make the surrounding air heated, expand and make a loud noise. This is thunder. 8. Why can an airplane fly into the sky? This plane has two wings, like those of a bird. It has a propeller.

The wing can generate lift and lift the plane into the air; Propeller can produce the ability to push the plane forward. Therefore, the plane can fly into the sky like a bird.

33. For a quartz clock hanging on the wall, when the battery runs out and stops, its second hand often stops at the position of "9" on the dial. This is because the second hand is most hindered by the large torque at the "9" position.

9. Before the water boils, the bubbles in the water rise and vibrate up and down due to convection. Most of the bubbles burst under the pressure in the water, and their cracking and vibration sound together with the container produce a * * * sound, so the sound is very loud. After water boils, it is isothermal up and down, and the bubble volume increases. Under the action of buoyancy, it will burst as soon as it reaches the water surface, so the noise is relatively small.

10. Fire-water incompatible substances must reach the ignition point when burning. Because of the large specific heat of water, water can absorb a lot of heat when it comes into contact with fire, thus reducing the temperature of ignition materials; At the same time, the vaporized water vapor surrounds the burning object, making it impossible for the object to contact with air. Without air, combustion cannot be carried out. 1 1. Sit on the ground and walk for 80,000 days. Because the radius of the earth is 6370 kilometers, every time the earth makes a circle, the distance that objects on its surface "walk" is about 40003.6 kilometers, about 80000 miles.

This is a poem sung by * *, which also scientifically reveals the relationship between motion and stillness-motion is absolute, and stillness is always relative to the reference object. 12. According to the principle of lever balance, if the power arm is a fraction of the resistance arm, then the power is several times the resistance.

If the weight of the arm is very large, it is entirely possible to "dial one or two kilograms." 13. When the distance between molecules is large (more than several hundred angstroms), the attraction between molecules is very small, almost zero, so it is difficult to reassemble a broken mirror.

14. If the directions of the components are the same, the resultant force is equal to the sum of the components. 15. Tofu can't be hung with hemp rope. When the pressure is constant, if the stress area is small, the pressure will be great.

16. True gold is not afraid of fire, and truth is not afraid of argument. Judging from the melting point of gold, although it is not the highest, it is 1068℃, while the temperature of general flame is about 800℃. Because the temperature of the flame is lower than the melting point of gold, gold cannot be melted. 17. With a long whistle, people in the valley should give a long whistle. After many reflections, the sound can form a loud echo, which lasts for a long time. As if the mountains were shouting and the valleys were echoing.

18. Looking at the sky from the well, you can see very little. Because light travels along a straight line, from the knowledge of geometric drawing, the frog's field of vision will be very small. 19. It can be seen from the pressure formula that when the pressure is constant, the smaller the stress area, the greater the pressure.

People will feel very uncomfortable sitting on such a blanket. 20. Good years are bright. Because snow is a bad conductor of heat, when it covers crops, it can well prevent heat conduction and air convection, so it can play a role in heat preservation.

2 1. It is cold before frost and cold after snow. In the late autumn night, the temperature near the ground suddenly turns cold (the temperature is below 0℃), and the water vapor in the air condenses into small ice crystals and adheres to the ground to form frost, so it feels "cold before frost". When snow melts, it needs to absorb heat to reduce the temperature of the air, so we have the feeling of "cold after snow".

22. Eggs touch stones-overreached eggs touch stones. Although the force is the same, the pressure that each object can bear is certain. If this limit is exceeded, the object may be damaged. Eggs can withstand less pressure, so they will break.

23. Before the jade is polished, the surface is uneven and the light is diffuse. After the jade is polished, the surface is smooth and the light is mirrored. 24. Fans have a cool breeze, which is suitable for summer but not for winter.

6. Popular science knowledge of primary school students

Ideal is a stone, knocking out a single spark; Ideal is fire, lighting the extinguished lamp; Ideal is a lamp that illuminates the road at night; Ideal is the road that leads you to the dawn.

In the age of hunger and cold, the ideal is food and clothing; In the era of food and clothing, ideal is civilization. In chaotic times, the ideal is stability; In a stable era, the ideal is prosperity.

Ideals are like pearls, one after another, running through ancient and modern times, stringing together the future, and the sky is endless. Beautiful pearl chain, the backbone of history, shines from the past to the present, and ancestors shine on future generations.

Ideal is a compass to guide ships; Ideal is a ship, carrying you to sea for a long voyage. But the ideal is sometimes the arc of the kiss of the sea and the sky, which is elusive and tortures your enterprising heart.

Ideal makes you smile and observe life; Ideal makes you stubbornly resist fate. Ideal makes you forget the early gray hair on your temples; Ideal makes your head white and naive.

Ideal is an alarm clock to break your golden dream; Ideal is soap to wash away your selfishness. Ideal is both harvest and sacrifice.

If the ideal brings you honor, it is only a by-product, and it brings more misunderstood loneliness, laughter in loneliness and bitterness in laughter. Ideal makes honest people often suffer misfortune; Ideals keep the unfortunate people alive.

Ordinary people are great because they have ideals; The ideal person is a "capitalized person". There are always people in the world who abandon their ideals, but ideals never abandon anyone.

Give new life to sinners, and ideal is the immortal grass that revives the soul; Call the prodigal son back, the ideal is a loving mother. The ideal is defiled, don't resent it, it's the devil testing your loyalty; Ideal has been pickpocketed, don't cry, go and get it back, and be careful in the future! Heroes lose their ideals, degenerate and mediocre, and boast of their achievements in those years in disgust; Mediocre people have lost their ideals and lived all their lives, ridiculously cursing the immediate environment.

Ideal flowering, peaches and plums should bear sweet fruit; The ideal bud, elm poplar will have thick shade. Please take the ideal horse and start with the whip. Spring has just started, and the sky is sunny.

7. Kneel for 10 scientific knowledge, each with three or four crosses.

Have a good sleep: poor sleep is related to the decline of immune system function. T cells in the body are responsible for dealing with viruses and tumors. If you don't get enough sleep, the number of T cells will decrease and the chance of getting sick will increase. You don't have to sleep for eight hours, and you wake up feeling refreshed in the morning.

Do some exercise: exercise for 30 to 45 minutes every day, the number of immune cells will increase and the resistance will increase relatively. However, if the exercise is too intense or lasts for more than 1 hour, the body will produce some hormones and inhibit the activity of the immune system.

Do * * *: * * to relax and reduce stress. 1 month for 45 minutes every day, the immune function will be significantly improved.

Daydreaming: Daydreaming for 5 minutes every day, taking a deep breath and daydreaming at the same time can increase the number and activity of immune cells.

Take part in an art activity: Laughter can significantly increase interferon and make immune cells more active. If you feel that you lack a sense of humor, you can watch more comedies and funny cartoons. Music can increase antibodies against infection and cancer. No matter what kind of music you like, you can have a healthy physiological reaction when you listen to it.

Communicate with your bosom friend once: people with many friends are not easy to catch a cold, and their immune function is better than those with withdrawn personality. Studies have shown that good social relations help to resist stress, reduce stress and affect immune cell function.

Pay attention to the method of heating in winter.

When the cold current comes, some people are shivering and try their best to keep warm, but nine times out of ten methods are not advisable, such as:

Active heating range is too strong. Doing more activities in winter can not only exercise, but also drive away the cold. However, for the elderly, we must do our best when exercising. Don't choose those sports with too much exercise, but choose jogging, cycling, playing Tai Ji Chuan and other sports with less exercise. If symptoms such as dizziness, headache, weakness of limbs, chest tightness, shortness of breath, insomnia and dreaminess appear after exercise, it means that the amount of exercise is too large, so we should pay attention to reducing the amount of exercise and stop the exercise with particularly bad reaction in time.

The method of dispelling cold and heating is out of order. Because most elderly people are afraid of the cold, they like to lie down with a hot water bottle when sleeping, or let the electric blanket heat the bed to keep warm, which often causes skin erythema or burns. Generally, when the room temperature reaches 18-25 degrees Celsius, it is also a suitable temperature for the human body, and no other means are needed for heating.

The sun is too long to keep warm. When winter comes, some old people like to take their grandchildren and move a chair to the dam to bask in the sun to keep warm. This is a good thing. Proper sunbathing is beneficial to the absorption of calcium, but doctors remind that sunbathing has a certain degree. Too long time is harmful to the body, because it will damage the skin, destroy the natural barrier of the human body, and make harmful chemicals and microorganisms in the atmosphere invade the human body, causing infection and vision loss. In particular, the skin of infants and young children is delicate and cannot be directly exposed to direct light for a long time.

Sleeping with your head covered is harmful to your health. Some old people like to sleep with their heads covered in winter, thinking that it can be warmer. This way of sleeping is harmful to health. On the other hand, due to the decrease of oxygen content in the bed, carbon dioxide and other waste gases gradually increase, which affects the normal breathing movement and even causes suffocation. Second, because of lack of oxygen in bed, cardiovascular and cerebrovascular diseases are easily induced.

8. What are the common scientific knowledge?

1. If the teeth are yellow, you can chew peanuts in your mouth and brush your teeth for three minutes to turn white;

2. If there is a small area of skin damage or burns, immediately apply a little toothpaste to stop bleeding and relieve pain;

3. Always leave ugly tea stains in the cup filled with tea, and wash it with toothpaste, which is very clean;

4. Open your mouth slightly when you look up at the eye drops, so that your eyes won't blink;

5. If there is an ulcer in the mouth, stick it on the ulcer with vitamin C, and it will basically be fine after the ulcer dissolves;

common sense

1. Detailed interpretation: that is, a mentally sound adult living in society should have basic knowledge, including survival skills (self-care ability), basic labor skills, basic natural science and humanities and social science knowledge. Are based on reverence for nature.

2. Source: Sun Yat-sen's "General Plan for the Founding of the People" III: "Anyone who wants to consolidate the heart of our country and correct the people's strength of our country must be familiar with this book. And spread it to the people of China, making it common sense. " Xia Mianzun and Ye Shengtao's Wen Xin V: "There are words outside the poem, which can be read. If you want to read their common sense, it doesn't hurt to read "White Elephant Ci". "

3. Interpretation of scientific common sense: refers to some things that happen in life and can be explained or solved by physical and chemical methods.

9. What little scientific knowledge do you know?

1. Rabbits beat the ground with their legs to transmit information, mostly with their hind legs, which is a way for them to express their feelings to female rabbits. 2. The biggest monkey in the world is a baboon and the smallest monkey is a bonobo. 3. The real name of "Four Elephants" is Elk, which is a rare animal in China. 4. Why does sorbet get angry?

The reason why sorbet bubbles is because there is a lot of invisible water vapor in the outside air. When it comes to cold sorbet, it will liquefy into droplets when it is cold. It seems that the sorbet is bubbling. 5. Why do sunflowers always face the sun?

Sunflower stems contain a wonderful auxin. This auxin is very afraid of light. When it is illuminated, it will go to the backlight side, and the cells on the backlight side will multiply rapidly. Therefore, the backlit side will grow faster than the bright side, which will bend the sunflower to light. 6. Why do cicadas shed their skin?

Cicada's shell (exoskeleton) is hard and can't expand with the growth of cicada. When the cicada grows to a certain stage, the cicada's exoskeleton restricts its growth, and the cicada loses its original exoskeleton, which is cicada slough. 7. How do bees make honey?

First, the bees spit the sweet juice of the flowers they picked into an empty hive. At night, they suck sweet juice into their honey stomachs to make it, and then spit it out and swallow it. It takes 100~240 times to make sweet honey. 8. Why do the stars twinkle?

We see the stars shining, not because the luminosity of the stars has changed, but because of the occlusion of the atmosphere. The atmosphere is between us and the stars. When starlight passes through the atmosphere, it will be affected by the density and thickness of the atmosphere. The atmosphere is not absolutely transparent, and its transparency will change according to its density. So when we look at the stars through it on the ground, we will see that the stars seem to be flashing.

10. What are the five great tricks in life to share with you?

Why do the stars twinkle?

We see the stars shining, not because the luminosity of the stars has changed, but because of the occlusion of the atmosphere. The atmosphere is between us and the stars. When starlight passes through the atmosphere, it will be affected by the density and thickness of the atmosphere. The atmosphere is not absolutely transparent, and its transparency will change according to its density. So when we look at the stars through it on the ground, we will see that the stars seem to be flashing.

Why do people yawn? When we feel tired, a lot of carbon dioxide has been produced in our bodies. When there is too much carbon dioxide, oxygen must be supplemented to balance the needs of the body. Because these residual carbon dioxide will affect our body's functional activities, then the body will send out a protective reaction, so we yawn. Yawning is a deep breathing action, which will let us breathe in more oxygen and expel more carbon dioxide than usual, and it can also eliminate fatigue.

Why can snakes walk without feet? Snakes have many scales, which are the outermost armor on their bodies. Scales are not only used to protect the body, but also to be their "feet". When a snake crawls forward, its body will be S-shaped. Every scale outside the S-shape will tilt upward to help the snake catch the uneven road when it moves forward. These scales cooperate with the muscles of the snake and can push the body forward, so the snake can walk without feet!

Why do sunflowers always bloom towards the sun? There is a substance called "auxin" in the stem under the sunflower disk. This substance has the function of accelerating replication, but it is anti-optical, and it will run to the backlight side whenever it encounters light. So when the sun rises, the stem of the sunflower immediately hides to the side of the backlight, as if the whole plant is bent in the direction of the sun.

Why does the hair turn white when people are old? There is a substance called melanin in our hair. The more melanin, the darker our hair will be. Without melanin, hair will turn yellow or white. When human beings reach old age, various functions of the body will gradually decline, and the formation of pigments will be less and less, so the hair will gradually turn white!