20-word question and answer on scientific knowledge

1. Little scientific knowledge is about 20 words. 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.

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. Moreover, every scale outside the S-shape will be inclined 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. 20 words in the fourth grade of scientific common sense

The mystery of automatic rotation

Thinking: Why do cartons full of water rotate?

Materials: empty milk box, nails, 60 cm long rope, sink, water.

Operation:

1. Punch five holes in the empty milk box with nails.

2. One hole is in the middle of the top of the carton, and the other four holes are in the lower left corner of the four sides of the carton.

3. Tie a rope about 60 cm long on the top hole.

4, put the carton on the plate, open the carton mouth, quickly fill the carton with water.

5. Lift the rope at the top of the carton by hand, and the carton rotates clockwise.

Description: the water flow produces equal and opposite forces, and all four corners of the carton are pushed by this force. As this force acts on the lower left corner of each side, the carton rotates clockwise.

Create:

1. If a hole is punched in the center of each side, how will the carton rotate?

2. If the hole is located in the lower right corner of each side, which direction will the carton rotate?

Boat and paddle

Thinking: Have you ever seen boating? Rowing by yourself? Do you know why the ship is moving on the water?

Materials: scissors 1, cardboard 1, rubber band 1, washbasin and water 1 basin.

Process:

1. Cut the cardboard into about 12cm * 8cm long.

2. One end of the bow is cut into a sharp shape, and the other end is cut out of the center of the stern by about 5 cm.

3. Cut a piece of cardboard about 3cm * 5cm to make ship pulp.

4. Tie a rubber band at the stern and tie an oar.

5. Turn the cardboard paddle counterclockwise and tighten the rubber band, and the boat will move forward.

6. If you turn the cardboard paddle clockwise to tighten the rubber band, the boat will move backwards.

Description:

1, the rubber band twists in different directions, but the ship's direction is just the opposite.

2. The power of paper boat movement comes from the energy of rubber band torsion.

About 4.20 words of scientific knowledge. Thank you.

Why does scientific sorbet get angry? The reason why sorbet bubbles is because there is a lot of invisible water vapor in the outside air. When encountering a very cold straight sorbet, it will liquefy into droplets and surround the sorbet when it gets 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 exposed to light, it will go to the backlight side, and the cells on the backlight side will multiply rapidly, so the backlight side will grow faster than the light side, which will bend the sunflower to the light side. 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.

5.20 Mathematical knowledge of words

People call 12345679 "Leak 8". This "number without 8" has many surprising characteristics, such as multiplying by multiples of 9, and the product is actually composed of the same number. People call this "uniform". For example:

12345679*9= 1 1 1 1 1 1 1 1 1

12345679* 18=222222222

12345679*27=333333333

……

12345679*8 1=999999999

These are all 0 times to 9 times of 65438+9.

And 99, 108, 1 17 to 17 1. Finally, the answer is:

12345679*99= 122222222 1

12345679* 108= 1333333332

12345679* 1 17= 1444444443

… …

12345679* 17 1=2 1 1 1 1 1 1 109

It is also a "uniform"

6. 20 words of science stories

Lewis carroll, whose real name is Charles Lutwidge Dodgson (1832~ 1898), is a mathematician. He has been a mathematics lecturer for a long time in the famous Christian College of Oxford University, and has published several mathematical works. Because of his severe stuttering, he is not good at making friends with people, but he has a wide range of interests, and he is quite accomplished in novels, poems and logic. He is also an excellent child photographer.

Alice in Wonderland was inspired by Carol. She wrote a story for her friend's daughter Alice and gave her own illustrations. Later, with the encouragement of friends, Carol revised, expanded and polished the manuscript, which was officially published in 1865. The story is about a little girl named Alice who chased a rabbit in her dream and fell into a rabbit hole. She started a long and thrilling journey until she finally clashed with the queen and king of poker and let out a loud cry. With magical fantasy, witty humor and lofty poetry, this fairy tale broke through the rigid formula of moral preaching in traditional children's literature in western Europe, and has since been translated into many languages and traveled all over the world.

Carol later wrote a companion piece called "What did Alice find there through the mirror", which was very popular because of Alice in Wonderland. Besides, Carol also wrote some poems, such as Snake Hunting and Jabberwocky.

7. Small knowledge of science and technology (about 50 words)

Meteor Meteor is a stone body in which cosmic meteors outside the earth leave their original orbit or are scattered on the earth into fragments. It is a precious and rare physical specimen for human beings to directly understand the stars in the solar system, which is of great collection value.

According to the observation of Canadian scientists in 10, more than 20 tons of meteorites landed on the earth every year, about 20 thousand pieces. Because most meteorites fall in sparsely populated areas such as oceans, weeds, forests and mountains, only dozens of meteorites are found and collected every year, and the number is very small.

Meteorite, when not falling into the earth's atmosphere, is a kind of stone, iron or a mixture of stone and iron floating in outer space. If it falls into the atmosphere, it will become a meteorite that we usually see falling to the ground without being burned by the atmosphere. Simply put, the so-called meteorite is the debris left by a tiny asteroid "hitting the earth". China is the first country to find meteorites in the world. It was in the Neolithic Age, and then it was recorded in writing until the end of the 20th century. There are many names marked by "meteorite", such as "Meteor Mountain" and "Meteor Lake".

Meteorites are generally divided into three categories according to composition, namely iron meteorites, also known as meteorites. Generally, the content of iron and nickel is above 95, including 80-95 iron and 5-20 nickel.

The density is 8 to 8.5. Other components may include sulfides, diamonds, rare earth elements and silicates.

Iron meteorites account for about 3 of the total number of meteorites. The world No.3 iron meteorite was discovered in Qinghe, Xinjiang, China at the end of 19, with a size of 2.42* 1.85* 1.37 and a weight of about 30 tons.

This meteorite contains 88.67% iron and 9.27% nickel. It contains many kinds of minerals that are not found on the earth, such as pyrite, zeolite and other cosmic minerals.

Supernova Sometimes, looking up at the starry sky, you may be surprised to find that there is a bright star in a certain star area that you have never seen before! However, after only a few months or even days, it gradually disappeared. This "strange" star is called a nova or supernova.

In ancient times, it was also called "guest star", which means "visiting star". Novas and supernovae are a kind of variable stars.

When people saw them suddenly appear, they once thought they were just newborn stars, so they were named "new stars". In fact, they are not only newborn stars, on the contrary, they are dying old stars.

In fact, they are exploding red giants. We have mentioned more than once that when a star enters old age, its center will shrink inward, while its outer shell will expand outward, forming a red giant.

The red giant star is very unstable, and one day it will explode violently, throwing its shell out and revealing the white dwarf or neutron star hidden in the center. In the Big Bang, the star will lose most of its mass and release huge energy at the same time.

In this way, in just a few days, its luminosity may increase by hundreds of thousands of times. Such stars are called "new stars". If the explosion of a star is more violent, its luminosity can even be increased by more than100000 times. Such a star is called a supernova.

The intensity of supernova explosions is unbelievable. It is said that the energy it pours out in a few days is equivalent to the energy emitted by a young star in hundreds of millions of years, so that it looks as bright as the whole galaxy! The explosion of nova or supernova is an important part of celestial evolution.

It is the glorious funeral of old stars and the promoter of new stars. The explosion of supernovae may trigger the birth of countless stars in nearby nebulae.

On the other hand, the ashes of nova and supernova explosions are also important materials for the formation of other celestial bodies. For example, many material elements on our planet today come from stars that have long since disappeared.

The volume of the sun is 6.5438+0.3 million times that of the earth, and it is the central celestial body of the solar system. An ordinary star in the milky way galaxy.

The average distance from the earth 1.496 million kilometers, the diameter 1.390 million kilometers, and the average density 1.409g/cm? 3. The mass is 1.989 * 10 33g, the surface temperature is 5770 Kelvin, and the center temperature is 15 million Kelvin. From inside to outside, there are the nuclear reaction area of the sun, the troposphere of the sun and the atmosphere of the sun.

Thermonuclear reactions continue in its central region, and the energy generated is emitted into space by radiation. One of the 2.2 billion energies radiates to the earth and becomes the main source of light and heat on the earth.

The sun is an ordinary star, and it has spent about half of its main sequence career on the Herro diagram. It is a hot gas (strictly speaking, plasma) ball with a mass of 1989 100 billion tons (about 330,000 times the mass of the earth) and a diameter of1392,000 kilometers (about 109 times the diameter of the earth).

Its average density is 1.4 times that of water, but this average density implies a wide density range, from the ultra-high density core to the thin outer layer. As a stellar sun, its overall appearance is luminosity of 38.3 billion watts and absolute magnitude of 4.8. It is a yellow G2 dwarf with an effective temperature of 5800 Kelvin.

The average distance between the sun and the earth around it is 149597870km(499.005 light seconds or 1 astronomical unit). By mass, its material composition is 7 1% hydrogen, 26% helium and a small amount of heavy elements.

The angular diameter of the circular surface of the sun in the sky is 32 minutes, which is very close to the angular diameter of the moon as seen from the earth. This is a wonderful coincidence (the diameter of the sun is about 400 times that of the moon, and the distance from us is just 400 times that of the earth and the moon), which makes the eclipse look particularly spectacular. Because the sun is much closer to us than other stars, its apparent magnitude reaches -26.8, making it the brightest celestial body on earth.

The sun rotates once every 25.4 days (average period; The equator rotates faster than high latitudes) and revolves around the center of the Milky Way every 200 million years. The sun is slightly flattened due to its rotation, which is 0.00 1% different from the perfect sphere, which is equivalent to a difference of 6km between the equatorial radius and the polar radius (the earth is 2 1km, the moon is 9km, Jupiter is 9000km, and Saturn is 5500km).

Although the difference is small, it is important to measure this flatness, because any slightly larger flatness (even 0.005%) will change the influence of solar gravity on Mercury's orbit, making the test of general relativity based on Mercury's perihelion precession unreliable. You think it's too long. You can cut a little from the middle.