We see stars shining, not because the stars change their brightness, but because the atmosphere blocks them.
There is an atmosphere between us and the stars. When starlight passes through the atmosphere, they will be affected by the density and thickness of the atmosphere. The atmosphere is not absolutely transparent, and its transparency will vary according to the density. Therefore, if we look at the stars on the ground through it, you will see that the stars seem to be flashing again.
2. Why do people yawn?
When we feel tired, our bodies have produced a lot of carbon dioxide. When carbon dioxide is in excess, it is important to increase the oxygen needed for body balance. Because these residual carbon dioxide will affect the function of our body activities, then the body will send out a protective reaction, so we yawn.
Yawning is a deep breathing action, which makes us breathe in more oxygen and release more carbon dioxide than usual, and it also has the effect of eliminating fatigue.
3. Why can snakes walk without feet?
Snakes have many scales on their bodies, which is the outermost layer of their body armor. Scales are not only used to protect the body, but also can be their "feet"
When a snake crawls forward, its body will be S-shaped. And every scale outside the S-shape will tilt, helping the snake move forward and catch the uneven road. The proportion of muscles is in harmony with the snake, and it can push the body forward when crawling, so the snake can move without legs!
4. Why do sunflowers always bloom towards the sun?
The place under the stem of sunflower chrysanthemum contains a substance called "plant growth hormone". This material has the function of accelerating reproduction, but it has the property of repelling optical rotation, and when it encounters light, it will move to the backlight side.
Therefore, when the sun rises, the sunflower's stem will immediately hide to the side against the light, and the whole plant looks bent in the direction of the sun.
5. Why does a person's hair turn white when he is old?
There is a substance called "melanin" in our hair. The more melanin, the darker the hair color. Melanin * * * is gone, and yellow or white hair will come out. When human beings reach old age, various functions of the body will gradually decline, and the formation of pigment will be less and less, so the hair will gradually turn white!
6. Why do fireflies glow?
Fireflies glow because there is a luminous device at the end of their abdomen, which is filled with some luminous phosphorus-containing luminescent enzymes, so fireflies can emit flashing lights.
Fireflies shine for purposes other than illumination, as well as mating, warning, trapping and so on. This is also a communication tool for them. Different kinds of fireflies emit light in different ways, with different frequencies and colors. They like to convey different information.
7. Why do you giggle when you are hungry?
When she is hungry, she will be called rolling. That's because the food is digested quickly before eating. Although her stomach is empty, she will keep secreting gastric juice. At this time, the contraction of the stomach will gradually expand, and the liquid and gas inside will come out and produce a rolling sound.
Don't put up with the embarrassment of cooing next time! Because this is a normal physiological action.
8. Why don't ostriches fly?
Very big ostriches, but they don't fly overhead, ah! This is not because their wings don't work, but because their feathers are too soft and their wings are too full to fly. In addition, the ostrich's muscles are developed and its sternum is flattened, which is of no help in flight.
Ostriches live in Africa. Because they have lived in desert areas for a long time, their bodies have gradually evolved into what they are now in order to adapt to the environment.
9. Why aren't perishable food and canned food in it?
Lunch meat, black bean shad, tomato sauce, canned beans. They are delicious food, and they can be stored for a long time without going bad easily. This is because canned food is sealed and bacteria can't enter.
When people make canned food, they will exhaust all the air in the canned food and then seal it. In the absence of air, even if some bacteria in food are not polluted, they can't survive or reproduce!
10. Why do newborn babies keep crying?
When you make all kinds of newborn babies cry, it's not because they are unhappy, but because they are the first people to take a big breath of air!
When babies leave their mother's body at birth, the first breath they breathe will rise to their throats, which will violently hit the vocal cords, make them vibrate, and then make a sound similar to crying.
1 1. Why does the lizard's tail keep bouncing off behind it?
In order to protect themselves, many soups are convenient for camouflage to deceive the public; However, when some lizards are attacked, their tails will be broken due to severe muscle contraction. Based on the broken tail, some nerves are still alive, and it will continue to bounce, thus distracting the enemy to escape. Don't think that your life is over like this. In fact, in just a few months, your tail will grow back and continue to live.
12. Why is the squirrel's tail so big?
Don't relax the mouse's tail! The squirrel jumps on the tree, and its tail plays a very useful role. It can keep the squirrel in the tree balanced when jumping and avoid falling. In addition, this kind of tail is obviously better in winter, which plays a protective role. It is convenient and practical to wind tightly around the squirrel.
13. Why can't a person have one or three thumbs?
Most people have five fingers, and the length of fingers is different. However, no one noticed that except the thumb, all other fingers have three, but only two thumbs? It turns out that this is in line with the meaning of the other four sessions. If it is three, then the thumb will appear powerless, and it can't carry heavy objects; If there is only one finger, it is not easy to grasp things with the other four fingers!
14. Why don't I scratch myself instead of feeling itchy?
Just like someone scratching their own itch, we will feel itchy and keep laughing; However, when scratching ourselves, we not only don't laugh, but also don't feel itchy. Because our minds are ready, the brain will send out the message that there is no danger, and the nerves have relaxed, so they won't laugh and feel itchy!
15. Why are most seawater blue and green?
Looking at the sea, it is also found that the sea water is blue and green in many places. However, when you pick up the water, you can only see it as transparent and colorless as the old water. It turns out that the sea itself is not much different from the water we contact daily, and it is transparent. The green we see is actually a phenomenon produced by the ability of water to absorb light. Only green water can be absorbed and reflected; As the water gets deeper and deeper, the green light is absorbed and the sea looks blue.
16. Why do you get goose bumps?
There are fine hairs on our skin, and there are erect pore muscles under each hair. When we are stimulated by nerves (such as anger, fear, cold, etc. ), the body temperature will drop, and the vertical hair muscles will contract, which will make the hair stand up and form goose bumps. In addition to insulation, such a physiological body system will make animals more capable of scaring enemies than they actually look.
17. Hippocampus when father was born?
Almost all animals' offspring are also bred by females, but the hippocampus is different. It is born by males. There is an incubator bag like kangaroo's "baby bag" in the abdomen of the male hippocampus, and the female hippocampus routes the male hippocampus into the incubator bag. After the male hippocampus assumes the responsibility of reproduction, after about three weeks, all the hippocampus will pop out of the father's body.
18. Why did the leaves change color?
Leaves change color because of its inherent chemical-chlorophyll. When autumn comes, the daytime is shorter than summer, but the temperature is relatively low, and the leaves stop producing chlorophyll, so the remaining nutrients are transported to the trunk and roots for storage. Green leaves show other chemical pigments without chlorophyll, so we can see more colors, such as yellow and brown leaves.
19. Why are there leaves?
Autumn is the time of ing, and the water evaporated on the leaves is more than that in summer, but the water absorption of the roots is less than that in summer. In order to reduce the water loss of trees, stem cells began to form a separation layer, which completely separated nutrients from the leaves. The separation layer separated the leaves from the trunk and the leaves fell off.
20. Why do whales spray water?
The whale is one of the mammals, but it has no nose, and its nose grows on its head. It lives in water and breathes with its lungs, which can save a lot of air at one time and does not need to go to the water surface for ventilation often. However, when it comes out for air, it will be used for nasal breathing, and the splash outside the body is made by huge pressure waves when breathing.