[Source: Science and Technology Network for Middle School Students | Time: 2006-4-1613:1:50] [Font: large, medium and small]

Every Sunday, I always finish the task of shoeshine given to me by my mother. Tell you, this is the source of my pocket money for a week! After getting the leather shoes covered with dust, I first wipe off the dust on the vamp, then apply shoe polish and wipe them carefully, and the leather shoes will become bright and beautiful. But why is this?

I found two pairs of old and new leather shoes of the same brand and style for comparative observation. I first touched the uppers of two pairs of leather shoes and found that the surface of the new shoes was much smoother than the old ones. Old leather shoes are coated with shoe polish. After careful polishing, it shines a lot, but it is still not as good as new leather shoes. Is there a relationship between the brightness of leather shoes and the smoothness of uppers?

I brought a pair of old leather shoes that were not polished, and the uppers were uneven under the magnifying glass. Then, I circled two rough areas A and B on the leather shoes. Carefully wipe area A with shoe polish, and area B without shoe polish as a blank control. I found that the surface of area A is obviously smoother after wiping, and it is more shiny than area B when placed in the sun. Why is there such a big difference between them?

I remember the teacher once said in science class that the wall surface of the theater is uneven, so that most of the sounds can be absorbed and the audience will not be disturbed by the echo. Similarly, light will be reflected on the surface of any object. If the plane is uneven, light will scatter in all directions. If this plane is smooth, then we can see the reflected light in a certain direction.

The surface of leather shoes is not absolutely smooth. If it is an old leather shoe, its surface is of course more uneven and can't reflect light in a certain direction, so it looks dull. There are some small particles in shoe polish, which can just be filled into the pits on the surface of leather shoes when shining shoes. If you wipe it with a cloth again, the shoe polish will be more uniform, the surface of leather shoes will become smooth and flat, and the reflective ability will be strengthened.

Through the experiment, I finally know the secret of shoes getting brighter and brighter!

My mother once told me such a riddle: "Zhuge Liang in Nanyang, sit tight." Arrange the eight diagrams and catch the flying generals. "This myth tells us that spiders only eat living things, but don't they eat dead things? This aroused my interest and I did the experiment.

I caught a little spider from the corner and put it in a box (with holes around it and glass on it for easy observation). Before the spider could weave a web, I picked up a dead bug and a dead fly and put them in front of the spider. The spider ignored them, then hit the box with her hand, and the spider crawled in other directions.

In order to find out whether spiders eat dead flies completely, the next day, I came to the box to observe and saw that dead insects and dead flies were still in their original places, but there was a net in the corner of the box, and the spider was lying quietly on the net. At this time, I thought: Is it because there is no net that the dead flies and insects didn't eat it yesterday? So I picked up the dead fly and gently put it on the net, but the spider still didn't move. Then, I gently touched the edge of the net with my pen. Gee, the spider seems to have a reaction and started to climb in a trembling direction. I took the pen back and the net stopped shaking. The signal was interrupted and stopped. Soon, the spider climbed to the center of the web again. I touched the dead fly's body on the net with the pen tip again, and the net began to vibrate, and spiders began to crawl here. I took back the nib again and the spider stopped. Like last time, after a while, the spider climbed to the center of the web again. Oh! I finally understand that spiders feel by the vibration of their webs and prey by weaving them. So, I recorded the experimental results.

In order to prove that spiders feel through the vibration of their webs, I did another experiment. Put the pen tip on the dead fly on the net and vibrate for a long time. The vibration of the web is getting bigger and bigger, and the spider seems to feel stronger and stronger. Spiders will come in a hurry. When a spider meets a fly, I will take back the pen tip, only to see that the spider's tail will soon spit out sticky silk to tie the fly, and then look at the spider's back, as if sucking the fly. Soon, there was a complete empty shell left on the Internet. This experiment proves that spiders eat moving insects.

Our secret group went to the library and bookstore to consult a lot of books about spiders. Among them, General Zoology wrote that spiders are carnivores, and their food is mostly insects or other arthropods. But your mouth has no upper jaw, so you don't swallow solid food directly, but suck it slowly. When insects and other animals come into contact with the net, they will struggle desperately on the net to make the net silk vibrate, so that spiders will find it soon. Spiders will crawl along the longitudinal silk to their prey, wrap the prey with spider silk and fix it on the net. First, the venom secreted by the poisonous gland in the claw limb is injected into the captured prey to kill it, then the digestive enzyme secreted by the midgut is injected into the captured tissue torn by the claw limb, which is quickly decomposed into juice, inhaled into the digestive tract, and finally eaten the remaining body shell. These fully prove that flying insects make the spider's web vibrate, and the web vibration will make it feel, and the spider will catch its prey if it feels. So it is confirmed that spiders only eat live animals, not dead insects.

Every Sunday, I always finish the task of shoeshine given to me by my mother. Tell you, this is the source of my pocket money for a week! After getting the leather shoes covered with dust, I first wipe off the dust on the vamp, then apply shoe polish and wipe them carefully, and the leather shoes will become bright and beautiful. But why is this?

I found two pairs of old and new leather shoes of the same brand and style for comparative observation. I first touched the uppers of two pairs of leather shoes and found that the surface of the new shoes was much smoother than the old ones. Old leather shoes are coated with shoe polish. After careful polishing, it shines a lot, but it is still not as good as new leather shoes. Is there a relationship between the brightness of leather shoes and the smoothness of uppers?

I brought a pair of old leather shoes that were not polished, and the uppers were uneven under the magnifying glass. Then, I circled two rough areas A and B on the leather shoes. Carefully wipe area A with shoe polish, and area B without shoe polish as a blank control. I found that the surface of area A is obviously smoother after wiping, and it is more shiny than area B when placed in the sun. Why is there such a big difference between them?

I remember the teacher once said in science class that the wall surface of the theater is uneven, so that most of the sounds can be absorbed and the audience will not be disturbed by the echo. Similarly, light will be reflected on the surface of any object. If the plane is uneven, light will scatter in all directions. If this plane is smooth, then we can see the reflected light in a certain direction.

The surface of leather shoes is not absolutely smooth. If it is an old leather shoe, its surface is of course more uneven and can't reflect light in a certain direction, so it looks dull. There are some small particles in shoe polish, which can just be filled into the pits on the surface of leather shoes when shining shoes. If you wipe it with a cloth again, the shoe polish will be more uniform, the surface of leather shoes will become smooth and flat, and the reflective ability will be strengthened.

Through the experiment, I finally know the secret of shoes getting brighter and brighter!

1. Small color projection needle

A magnetic needle is a compass. Compass is one of the four great inventions in China. In the present physics teaching, a small magnetic needle can be used to judge the direction of the magnetic field. However, it is very inconvenient to use magnetic needles sold in the market or investigated and dialed by higher authorities. When the teacher is doing the demonstration experiment of magnetic field direction, the students can't see clearly below, so the teacher has to take the instruments down and show them to the students one by one, which is very time-consuming. What shall we do? After trying their best, the students finally made a simple color projection magnetic needle, which can be used as a compass and projected on the projector, so that the whole class can see the direction of the magnetic field, which provides great convenience for teaching experiments. 、

Simple projection needle has simple structure and common materials. It is made of card pins, pins, plexiglass strips and transparent projection film materials. The manufacturing method is: put two steel needles on the two steel needles respectively, and pay attention to the balance of the two steel needles. Then cut the transparent film into sharp long pieces, stick it on the steel needle with 502, one at each end, pay attention to symmetry, and then paint it red and green respectively. So as to complete that upper part of the magnetic needle. Saw the plexiglass strip into a block, then grind it into a round base of the magnetic needle, and iron it in the middle of the round plexiglass. Please note that the pin should be perpendicular to the base. The inner groove of the small snap button is used as the bearing support hole for rotation. Put the bearing on the needle tip, so that the magnetic needle will rotate on the needle tip. The last one is to wipe the S pole of the bar magnet from the middle of the magnetic needle to the green side, and magnetize the small magnetic needle, that is, the N pole. So that the small magnetic needle is magnetized.

Put the self-made small magnetic needle on the projector, and you can see the direction of each point of the magnetic field at a glance from the curtain.

2. Why can clothes keep people warm?

First of all, you should ask yourself: Can clothes really keep people warm?

You know, it's not leather that keeps people warm. On the contrary, people keep fur coats warm. Right? You know a fur coat is not a stove. "What?" You will ask. "Is that man a stove?" Yes, man is a stove! We already know the food we eat-this is chopping wood, which burns in our bodies. At this time, we didn't see any sparks. We say it is burning only because we feel that there is heat in our body.

This heat needs to be protected. In order to prevent the heat in the house from spreading to the street, we built thick walls, installed double windows in winter, and wrapped blankets on the doors. We wear clothes for the same reason. Instead of letting our body's heat radiate to the indoor air or the street, we keep our clothes warm, which keeps our heat around our bodies. Of course, our clothes also give off heat, but it is much slower than our bodies.

3.[ Scientific Papers] Energy-saving street lamps

The Chinese nation has a fine tradition of thrift, and the people of China have maintained this good style since ancient times. This feature is also reflected in productive labor and daily life. We should always try our best to do everything well in the most economical way. It is because of this good idea that we know how to save energy. The energy problem is of extraordinary significance to a populous country like China. With the development of economy and the large-scale exploitation of resources, the problem of energy shortage has become more prominent, which has greatly affected the modernization of China. Up to now, our country still advocates thrift. In the major construction of Olympic venues, the state put forward the slogan of "running the Olympic Games frugally" according to the actual needs. On the 55th anniversary of the National Day this year, the slogan "Save the National Day" was put forward one after another. Our country is proceeding from the overall situation and achieving the diligent style from the aspect of energy conservation. Saving energy can reduce expenses, promote economic growth and protect the natural environment, which is also a prerequisite for taking the road of "sustainable development" and for our future generations.

At night in the city, there are dense and neat street lamps on both sides of the road, which looks like a dragon flying. Although this is a beautiful scenery, many times the lights of these street lamps are wasted because the road is empty for a large part of the time, especially in areas with underdeveloped economy and transportation. The huge waste of power resources has brought negative effects on the economy of these areas, which is not beneficial, but harmful. Then, is there an automatic control device that is convenient for pedestrians and vehicles to pass at night and saves energy?

Saving energy is actually to reduce energy loss as much as possible. On remote roads, the traffic flow is very small, and turning on street lamps for a long time, whether there are cars, no cars, pedestrians or no pedestrians, will cause great waste of energy. You shouldn't turn on all the road lights even if a car passes by. You should only turn on the street lights within the effective range of the vehicle, otherwise it will cause great losses! So do pedestrians walking on the road. Only turn on the street lamps within the corresponding range for pedestrians to meet the lighting needs. This problem can be compared with the common voice switch now. As long as someone walks in the stairwell and makes a sound, the light will light up when the vibration generated by the sound is transmitted to the voice control switch, and the light will only light up within the pedestrian's walking range and will not light up for a long time. From this, we can know that when vehicles and pedestrians pass on the expressway, don't they exert pressure on the pavement? If there is an inductor that can automatically control the switch under the pressure and control the lights on and off within the corresponding range, the purpose of energy saving will be achieved.

Then this sensor can not be controlled by air vibration generated by sound, but by road vibration generated by the impact and pressure of vehicles and pedestrians on the road. These two kinds of vibrations are different, otherwise it is a mistake, which may be the barking of animals. The noise outside the road will turn on the lights, and it will also fail to achieve the purpose of energy saving. If the noise from vehicles and pedestrians is very small, the lights will not light up? That's useless. It doesn't work at all. The driving of cars and the walking of pedestrians will naturally produce impact and pressure on the ground, which will make the road surface vibrate, so that the road surface vibration can be used to control the opening and closing of street lamps. If there is such a device, it can be installed in the light box of a street lamp, and each device is connected to the road surface with a metal bar. When the road surface is impacted and vibrated by pressure, the corresponding street lamps will light up, and the lights will light up where there are vehicles or pedestrians, and the vibration will stop, and the lights will automatically go out within a certain time limit. This device uses vibration and pressure to control street lamps, which can play a very good role in energy saving. Of course, in order to reduce the number of installed devices, such a device can control multiple street lamps, and multiple devices are connected in parallel in a circuit, that is, one device is installed at intervals, and then these devices are connected to the corresponding street lamps through wires. We might as well name it "vibration sensor" first. Let's first look at the working principle of the "vibration sensor": First, the metal bar is used to sense whether the road surface vibrates. When a car or pedestrian passes a certain road section and exerts pressure on the road surface to generate vibration, the metal bar transmits the vibration to the "vibration sensor", which is stimulated by the vibration and commands several street lamps it controls to turn on the switch. Vehicles and pedestrians continue to pass the next road section, and the "vibration sensor" of the next road section is also stimulated by vibration, which also lights up the corresponding street lamps, and so on. At the same time, the "vibration sensor" on the road section after vehicles and pedestrians passed by turned off the switch because it did not continue to receive the vibration information transmitted to it by the metal strip, so that the corresponding street lamps did not continue to emit light. But this kind of "vibration sensor" requires high sensitivity and can also identify the vibration source. For example, under special circumstances, lightning weather or high-decibel noise generated by factories will make the air vibrate violently, and it will also be transmitted to the "vibration sensor" through metal bars. The "vibration sensor" mistakenly thinks that the vibration comes from the road surface, which makes the street lamp shine. Therefore, we need to use science and technology to study and develop a novel. Huh? Don't say that. Apricot ζ ao is out of danger? Visit? Blow molding? So the sheath is charming? Hey? Scratches? Blow?

Well, as long as this "vibration sensor" is installed on the road with street lights, it doesn't need a lot of manpower to control the power supply, and all the work will be automatically controlled by the machine. We can imagine that there are cars or pedestrians passing by on the road, and the scene of street lamps flashing and going out for the second time is dazzling and overwhelming. Isn't evening a unique and beautiful scenery? At the same time of convenient transportation, the biggest advantage is that it saves energy greatly.

This kind of "vibration sensor" is designed to save energy. I hope this device can be applied to practice and play a great role. While developing the economy, we must not ignore the importance of energy conservation, save energy and take the road of sustainable development, which has become the common sense of mankind.

The importance of trees to human survival

Trees are indispensable things in our life. There are fewer and fewer trees now, all because of deforestation in the past. Now, the society is advocating: take care of trees and plant more trees! What are the benefits and importance of trees to people? What are the benefits of planting trees? In order to discuss these problems, I made in-depth observation and analysis.

Without trees, there is not enough oxygen and food, and there is no one. So trees are very important, full of benefits and harmless. Therefore, everyone should protect every tree and make contributions to environmental protection!

So, what are the benefits of trees? After investigation, I found that trees have five advantages:

1. Trees can regulate climate and keep ecological balance. Through photosynthesis, trees suck in carbon dioxide and spit out oxygen, and the air becomes clean and fresh. An acre of forest releases enough oxygen for 65 people to breathe.

2. Trees can prevent wind and fix sand, keep water and soil, and absorb all kinds of dust. An acre of forest can absorb 20-60 tons of dust a year.

3. Forests can reduce noise pollution. A 40-meter-wide forest belt can reduce noise 10- 15 decibels.

The secretions of trees can kill bacteria. There are 34,000 bacteria per cubic meter of air in the open space, while there are only 3,400 bacteria in the forest.

Trees growing in cities themselves can green our environment and form beautiful scenic lines;

Leaves can interact with sunlight, absorb carbon dioxide, release oxygen, purify the air and give people the oxygen necessary for breathing.

Planting trees has many advantages: it can purify the air, beautify the environment and green the motherland. It can also make oxygen in the carbon dioxide exhaled by people for people to absorb and breathe. If a large number of trees are not planted, the oxygen on the earth will be difficult to meet the needs of human beings and all kinds of creatures.

Afforestation can also reduce noise. Noise pollution has caused great harm to human life, study, work and rest, and can be said to be people's "enemy". Therefore, we should pay more attention to afforestation. Noise can also lead to hearing loss, deafness and stupidity, as well as heart, blood pressure and nerve abnormalities in long-term life. Even, it can make people die under long-term noise. In this way, afforestation can reduce noise by four or five times.

Afforestation not only has very important environmental benefits for human survival, but also has great economic benefits for human production and life. The unreasonable exploitation and utilization of natural resources by human beings is the main reason for ecological imbalance. Deforestation, deforestation, overgrazing, etc. It will destroy forests and grasslands, cause soil erosion and land desertification, and make sandstorms occur frequently. Unreasonable development and occupation of land make the cultivated land area decrease day by day.

Afforestation plays an important role in maintaining ecological balance, with the functions of producing oxygen, purifying air, conserving water, conserving soil and water, regulating climate, preventing wind and fixing sand, and eliminating noise. Now that we know so many benefits of afforestation, we should consciously fulfill the obligation of afforestation and lay the foundation for creating our beautiful home.

In order to contribute to the country, we primary school students can also help! Establish environmental awareness and protect our garden. (1) On campus, you can actively participate in the activities of creating a "green campus" and make necessary knowledge reserves for participating in and carrying out broader environmental protection actions; (2) Around the family and community, do some activities that we can do, such as planting flowers and trees, improving environmental sanitation, creating a beautiful living environment, protecting birds, saving water, recycling used batteries, not using disposable chopsticks, and promoting environmental protection knowledge. (3) Participate in and promote community environmental protection, pay attention to and actively participate in environmental protection actions, and drive more people to participate in environmental protection actions.

Through a series of investigations, I know that trees have many benefits and are very important for human survival. Everyone should plant trees to make our future more beautiful and rich!

Change the weather artificially

During the rainy season, I often hear guns rumbling in my hometown, which is to increase rain and prevent hail. In fact, it can also eliminate the rain.

After a long drought, there was rain, and a few guns went up, which immediately brought a timely rain to farmers; Hail is coming, and a few bombardments will make the grapes everywhere no longer chaotic and the grains will not be harvested; Yichun city, Heilongjiang province, continued to artificially increase rainfall to help forest areas extinguish fires; The Olympic Games will also adopt the method of eliminating rain to control the rainfall time.

So how do people affect the weather? Different clouds, different regions, different purposes and different methods.

When the clouds in the air can't have enough precipitation, dry ice, salt or calcium chloride, silver iodide, etc. You can sow seeds in the cloud by plane, rocket, etc. , can enhance artificial precipitation. Coolant, such as dry ice, makes the temperature in the cloud drop significantly, and makes tiny water droplets and ice crystals increase rapidly, forcing them to drop and form precipitation; A coagulant with strong hygroscopicity, such as salt, makes cloud droplets grow into raindrops and fall down; Crystallizers such as silver iodide can produce a large number of artificial ice cores, which can participate in the microphysical process of cloud precipitation under suitable conditions, so that more water vapor and cloud droplets can be transformed into precipitation. There are also powerful shock waves produced by bombarding clouds with soil cannons and soil arrows, which make cloud droplets collide with each other and merge into raindrops to land.

Artificial precipitation enhancement can be divided into "precipitation in advance" and "precipitation suppression". Among them, "early precipitation" refers to artificial precipitation enhancement in the windward side and surrounding areas of the reserve, and the temporal and spatial distribution of rainfall is adjusted so that it does not rain or light rain in the reserve. "Suppression of precipitation" refers to excessive sowing of liquid nitrogen and silver iodide to disperse clouds and weaken precipitation.

Artificial hail suppression means that when the hail cloud appears, it is bombarded with anti-aircraft guns or special soil guns and rockets, and the powerful shock wave generated by explosive explosion makes the hail in the cloud collide with each other, and the big hail breaks into small hail, and the small hail falls and melts into raindrops; Or under the action of shock wave, supercooled water droplets in the cloud (the temperature is below 0℃ and unfrozen raindrops) become ice crystals (supercooled water droplets freeze rapidly when shaken), thus changing the state of ice water, destroying the conditions of hail occurrence, making ice crystals in the cloud fall instead of hail, and achieving the purpose of preventing hail disasters.

Qinhuangdao 10 rockets, 2 rockets from lulong county. In addition, there are 20 anti-hail Sanqi anti-aircraft guns distributed in counties and districts, and there are 2 guns in lulong county.

With the rainy season in Qin city, the meteorological department of Qin city has carried out more than 50 rocket precipitation enhancement operations this year and fired more than 300 rockets; Anti-aircraft guns have been engaged in hail suppression operations for nearly 20 times and fired nearly 600 hail suppression bombs. In Huyuan Village, Caigezhuang, Beidaihe, Duanjiadian, Shanhaiguan and Changli, Mazhuang in Anshan Town, Xiazhai and Mu Jing Township in lulong county, and Guo Chang Village, Shimenzhai, Dashantou, Shuangling and Qinglong in Funing County, more than 40 operating points have been set up to carry out irregular hail suppression and precipitation enhancement operations.

Due to the failure to deploy the attached parachute during the launching of the GRP rocket for rain enhancement and hail suppression, it fell rapidly from a height of 600 meters and finally landed on the roof of a farmhouse in Funing, smashing a big hole. Therefore, the meteorological department appealed that if the people near the job site found the parachute of the rocket and found the wreckage of the rocket and shell with the words of artificial precipitation enhancement or artificial hail suppression, they should not disassemble it themselves and contact the local meteorological department in time to avoid accidents.

You can see outsiders without opening the door.

Someone knocks at the door or rings the doorbell, but you can only hear the sound but can't see anyone. If you open the door hastily, you will sometimes get into trouble. For the sake of safety, some houses have installed building intercom and TV monitoring equipment on their doors, so people outside can be seen without opening the door.

Building intercom and TV monitoring equipment consists of two parts, which are installed in the door and the door respectively. The part installed outside the door has a camera and a dedicated speaker. The camera is equipped with a photoelectric replacement lens, which can convert the scene image into corresponding electrical signals for output. The speaker is dual-purpose and designed to have dual functions of sending and receiving calls. The components installed on the door are TV monitor and telephone. The TV monitor can also use the existing TV set at home. Outdoor and indoor equipment shall be connected by cables.

When someone knocks at the door, the camera will record the image of the person and transmit it to the TV monitor in the door through the cable. In this way, people's images will appear on the monitor screen. At this time, people inside and outside the door can talk and communicate through the phone and speakers, thus accurately distinguishing people outside the door.

Building intercom and TV monitoring equipment can be installed on a single door, or on the entrance and exit doors of whole houses, office buildings and institutions with hundreds of rooms. According to the numbers of rooms in the building, buttons with corresponding numbers are installed outside the main entrance, and unified management is carried out after networking through the computer center. When someone comes outside the main door, just press the button in a room, and the computer will send the image and sound signal of the visitor to this room, so that the owner can distinguish it after contacting. If the host agrees to let people in, the computer will give instructions to open the main entrance to let people in. The computer can also record the time when people enter the door for verification, which plays a better role in security.

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