What should primary school students know?
Scientific knowledge is the sum of knowledge and experience gained by human beings in the practice of transforming the world, including empirical knowledge and theoretical knowledge. Let's introduce some scientific knowledge to the children. Let's get to know it together!
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 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 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.
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.
Why is the sea mostly 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 seawater itself is not much different from the water we touch every day, and it is also transparent. The green we see is actually a phenomenon caused by the ability of seawater to absorb light. Only green light can be absorbed and reflected by seawater; When the seawater is deep, the green light is also absorbed, and the seawater looks blue.
Why do leaves change color?
The reason why leaves change color is related to the chemical substance chlorophyll. When autumn comes, the days are shorter and the temperature is lower than that in summer, so the leaves stop producing chlorophyll, and the remaining nutrients are transported to the trunk and roots for storage. Leaves lack green chlorophyll and other chemical pigments appear at the same time, so we often see yellow and brown leaves.
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 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.
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.
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 snake's muscles and can push the body forward, so the snake can walk without feet!
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!
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.
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.
Why can't the food in cans go bad easily?
Lunch meat, black beans and ketchup beans are all delicious canned foods, which can be preserved for a long time and are not easy to deteriorate. 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!
Why do babies 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.
Why do lizards keep playing backwards when 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.
Why can't a person's thumb have one or three knots?
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!
Why not tickle 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!
Why is the sea mostly 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 seawater itself is not much different from the water we touch every day, and it is also transparent. The green we see is actually a phenomenon caused by the ability of seawater to absorb light. Only green light can be absorbed and reflected by seawater; When the seawater is deep, the green light is also absorbed, and the seawater looks blue.
Why do you get goose bumps?
Hair grows on the surface of our skin, and there is a vertical hair muscle under each pore. When stimulated by nerve (such as anger, fear, cold, etc. ), the body temperature will drop, the vertical hair muscles will contract, making the hair stand up and form goose bumps. In addition to keeping warm, this physiological system can make animals look bigger than they really are, thus scaring off enemies.
Hippocampus was born in dad's belly?
Almost all animals are females, but the hippocampus is different. It's male. On the belly of the male hippocampus, there is an incubator similar to a kangaroo "pouch", and the female hippocampus will discharge the eggs into the incubator of the male hippocampus. Since then, the male hippocampus has assumed the responsibility of pregnancy. In about three weeks, the little sea horse will pop out of his father's body.
Why do leaves change color?
The reason why leaves change color is related to the chemical substance chlorophyll. When autumn comes, the days are shorter and the temperature is lower than that in summer, so the leaves stop producing chlorophyll, and the remaining nutrients are transported to the trunk and roots for storage. Leaves lack green chlorophyll and other chemical pigments appear at the same time, so we often see yellow and brown leaves.
Why are there fallen leaves?
It's fall here. Leaves evaporate more water than in summer, but roots absorb less water than in summer. In order to reduce the water loss of trees, stem cells began to form separation layers. When the nutrients leave the leaves completely, the separation layer separates the leaves from the trunk and leaves fall off.
Why do whales spray water?
A whale is a mammal, but its nose has no shell, and its nostrils grow on the top of its head. Living in water and breathing with the lungs can store a lot of air at a time, and you don't need to breathe on the surface often. But when it breathes to the surface, it breathes through its nose. When it breathes, the huge sound waves emitted by the sea water are caused by pressure.
How big is the Milky Way?
Many stellar systems combine to form a huge galaxy, and the galaxy where the solar system is located is called the Milky Way. The Milky Way is like a big discus, with a width of about 80,000 light years, a center thickness of about 1 0.2 million light years, and a total number of stars exceeding10,000.
Why can't you see the stars during the day?
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.
What celestial bodies are there in the solar system?
There are eight planets in the solar system. They are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. 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.
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.
What is thunder?
A: 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.
Why can planes fly into the sky?
A: An airplane has two wings. Just like the wings of a bird, it also 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.
Why is a bottle full of water not easy to break?
There are two identical glass bottles, one is empty, the other is full of water, and at the same time it falls to the ground from the same height. Which bottle breaks easily? Generally speaking, heavy bottles break easily. But when the bottle is filled with water, the water in the bottle has another function, which can reduce the deformation of the bottle and make it difficult to break. Most of the broken glass bottles are caused by deformation. When the empty bottle falls to the ground, the pressure is constantly exerted on the bottle, and the bottle is deformed from the outside to the inside and finally breaks. The bottle is full of water. Because water is incompressible, the deformation is reduced and the bottle is not easy to break. The bottle is filled with water, and then the cap is tightened, so it is more difficult to break.
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Common sense of China culture that primary school students should know.
Age appellation
Baby: a baby under one year old.
Childhood: refers to children aged 2-3.
Crying: refers to children (also called "total angle")
Cardamom: refers to a thirteen-year-old woman.
And logistics: refers to a fifteen-year-old woman.
Crown: refers to a twenty-year-old man (also known as "weak crown")
Thirty years old: refers to thirty years old.
There is no doubt about age: it means forty years old.
The year of know life: refers to 50 years old (also known as "knowing destiny" and "half a century old")
Sixty years old means sixty years old.
Seventy years old: It means seventy years old.
Eighty or ninety years old: refers to eighty or ninety years old.
Happy age: 100 years old
Ancient major festivals
January 1 ST: The first day of the first month, the year begins.
People's day: the seventh day of the first month, master.
Shangyuan: On the fifteenth day of the first month, lanterns are played, which is also called "Lantern Festival".
Social Day: Around the vernal equinox, sacrifices are made to pray for farming.
Cold food: two days before Tomb-Sweeping Day, three days without fire (Wu Zixu)
Qingming: Tomb sweeping and sacrifice in early April.
Dragon Boat Festival: On the fifth day of May, we eat zongzi and row a dragon boat (Qu Yuan).
Tanabata: On the seventh day of July, women seek cleverness (Cowherd and Weaver Girl).
Zhongyuan: July 15th, also called "Ghost Festival".
Mid-Autumn Festival: August 15th, homesick for enjoying the moon.
Chongyang: On the ninth day of September, climb the mountain and insert dogwood to avoid disaster.
Winter solstice: also called "solstice", the starting point of solar terms.
Twelfth lunar month: On the eighth day of twelfth lunar month, drink Laba porridge.
New Year's Eve: the last night of the year, the beginning of the old year and the beginning of the new year.
Wedding anniversary 1 year: paper wedding, cotton wedding, leather wedding, fruit wedding, wooden wedding, iron wedding, bronze wedding, ceramic wedding, willow wedding and aluminum wedding in the second year. /kloc-ivory marriage in 0/4 years,/kloc-crystal marriage in 0/5 years, porcelain marriage in 20 years, silver marriage in 25 years, pearl marriage in 30 years, coral wedding in 35 years, ruby marriage in 40 years, sapphire marriage in 45 years, golden marriage in 50 years, first place.
Imperial Examination Officer [after having obtained the township examination]: The applicants are named Juren, Xie Yuan and Exam; The enrollment was named "Gong Sheng", and the first names were "Huiyuan" and "palace examination"; The enrollees are called "Jinshi", the first one is the "champion", the second one is the "champion" and the third one is the "champion".
Hamlet, King Lear, Macbeth and Othello.
Poker role
Spades J: Attendant of Charles I, Hokkala.
J of hearts: Lahaiya, the court attendant of Charles VII.
J of clubs: Lancelot, a famous knight of King Arthur.
Box j: Roland, the attendant of Charles I.
Q of Spades: Athena, Wisdom and Sivir in ancient Greek mythology.
Q of hearts: Jules, German, wife of Charles I.
Club Q: Queen York of Lancaster, England.
Q: In the Old Testament, it was Joseph's sister, Queen Raquel.
Spades K: David, the father of King Solomon of Israel in 10 BC, was good at playing the harp.
King of hearts: Charles I, King scharmann of the Franks.
Club K: Alexander the Great of Macedonia, the earliest world of Go.
Box K: Julius Caesar, a famous Roman soldier and politician, became an autocratic ruler after the unification of Rome.