I myself am going to take a day off, and the unit suddenly has an emergency, and I am busy until now.

The first and second sections of this popular science article by Manager Mei Lezhi are being rewritten, and the third chapter will be sent first.

Section 3 Gravity - Buoyancy

Walking on the earth, you can feel the influence of gravity, for example, climbing a mountain is more tiring than walking on a flat road. However, the person who consciously thought about and analyzed this question was the Englishman Newton. Perhaps others have analyzed it before Newton, but no documentation has been found. Newton discovered that objects on Earth that lack support always fall on the ground, while the Moon is always hanging in the air, and the reason for this is that the Earth is attractive to any object, which we usually call gravity. And the moon has been moving away from the earth, and the earth is attracting the moon, and the two are just in balance. If the Moon had moved away a little more, the Moon would have disappeared without a trace. If the attraction of the Earth were greater, the Moon would plunge headlong into the embrace of the Earth. But there is no need to marvel at our luck, those satellites that are far from the trend and the attraction are not balanced, long gone. Only those who have reached equilibrium can wait until we appear.

Gravity allows the atmosphere to exist and the oceans to form. Water has weight, and since most of our bodies are water, we are roughly equivalent to a humanoid water bladder. The atmosphere also has weight, and this weight is pressed on us, which is atmospheric pressure.

Swimming or walking around in the water is a struggle compared to running on the ground. Running on the ground, on the other hand, is actually done in the atmosphere, but the difference in sensation is so great because the atmosphere is much thinner than water. Of course, if you run fast, you can feel the strength of the oncoming wind increasing.

Atmosphere:

The thickness of the atmosphere we live in can be up to 2,000 kilometers, but in fact, more than 10 kilometers from the ground is very thin. (On Earth, the height of the ground changes dramatically, and using the sea surface as a basic indicator of height can ensure that the number is uniform.) So the altitude behind is based on sea level, which is called altitude. More than 100 km, it can be completely ignored. For what we can actually touch, 10 kilometers from the ground, named the troposphere, the atmospheric phenomena that we see, such as wind, rain, thunder, and so on, all happen here. Within the troposphere, the average temperature is decreasing as the altitude increases. From 10 km to 50 km, is the stratosphere. The air here is thin and almost devoid of moisture, and the temperature is constant in areas at the same altitude, maintaining minus 55 degrees Celsius at an altitude of 10 km. As the altitude increases, the temperature increases. After the altitude rises to 30 km, the temperature rises to about 0 degrees. Today's airliners maintain stratospheric flight.

This hundreds of kilometers of atmospheric pressure on us is the atmospheric pressure we normally bear, which is defined as 1 atmosphere. Why didn't such a thick atmosphere crush us? We have the pressure inside us that is just out of balance with the atmospheric pressure outside, so we're fine. If the internal and external pressures are out of balance, something will go wrong. Now space technology has made it possible to go into space, where the atmosphere can be completely ignored. In this way, there is no external equilibrium in the internal pressure, and all the gas in the lungs is lost, and the gas in the abdominal cavity will be extremely inflated. When astronauts repair spacecraft in space, they wear thick spacesuits to ensure the balance of external pressure in the human body, provide air to breathe, maintain body temperature, and so on. On Jupiter, there is also a thick atmosphere, and the attraction of Jupiter is much greater than that of Earth, so the atmospheric pressure there is much greater than that of Earth, and we will be flattened there.

Nowadays, tourism is popular, and people living along the coast travel to the plateau and often have altitude sickness. This is not due to the difference between the internal and external pressures, as the internal and external pressures of the body slowly enter a state of equilibrium. Rather, it is caused by the fact that as the altitude increases, the atmosphere gradually becomes thinner, and the supply of oxygen needed by the human body is insufficient. In addition, the altitude increases, and the temperature of the atmosphere decreases slowly. The average temperature of the plateau decreases, and the temperature difference between day and night increases, which also contributes to physical discomfort. A better solution is to do physical exercise some time before the trip, mainly to enhance the heart and lungs, such as swimming.

Observe:

1What if you experience changes in atmospheric pressure at different altitudes? When taking the train, if you pass through the plateau (high altitude) from the plain (low altitude), or reach the plateau. If you stay quiet or sleep for a long time, you will notice tinnitus or ear pain, and you will hear sounds that are louder than you actually are. This is because of the imbalance between the pressure of the enclosed space of the inner ear and the atmospheric pressure outside. This can also be the case when flying in. How to fix it? A few deep yawns allow the inner ear to exchange air with the outside, restoring pressure balance. If you're lucky, you can hear the air flow in and out of your inner ear, but it's not pleasant.

2. How to experience the difference in altitude and the difference in atmospheric thinness? People who live at low altitudes, after arriving at high altitudes, will spontaneously take deep breaths to compensate for the lack of oxygen supply due to the thin atmosphere. Usually people take deep breaths occasionally, and at this time they take deep breaths throughout the whole time. The premise is that the cardiopulmonary function is normal enough, otherwise you can only stay with the oxygen tank or go home

(This chapter is not finished, please turn the page). Similarly, after sitting for a long time, the breathing is always in a shallow breathing state, and the oxygen supply is insufficient. At this time, yawning and stretching are all spontaneous actions of oxygen. When the oxygen supply is insufficient for a long time, the body will adjust to reduce the need for oxygen and enter a dormant state. The same effect can be achieved with an increase in carbon dioxide levels. So when you enter an enclosed space, cave, etc., and find yourself sleepy, this is a danger signal, and leave quickly, otherwise you won't leave.

3If you have the opportunity to take a plane, you can see from the observation window that at any time, the sky is clear, and those thunderbolts are under the plane. At this point, you're in the stratosphere. If you notice clouds around the plane, it must be that the plane is not high enough.

4 In some areas, warm and moist air is blown towards the mountains, and as the height of the mountains increases, the temperature drops, and the water vapor in the air condenses into water and falls to the ground in the form of rain. This is the rain that forms on the ground. Yucheng in China has Ya'an, Sichuan and Keelung, Taiwan. The rain city of the world is Girapunzi in India, where it can rain for several years in a row. It rains due to the terrain. In other places, the air crosses the mountains into the valleys, where the terrain compresses and the temperature increases rapidly as the altitude decreases. However, the water vapor in the air does not increase, the air appears dry, and the higher the temperature increases, the drier it becomes. Foehn is formed. For example, Sun Valley in Derong, Sichuan, and Silicon Valley in California, USA. Observe the nearby area and look for terrain rain and foehn winds. This is a very common phenomenon in itself, and when you go out to travel, you can estimate the direction of the wind by observing the difference in vegetation on both sides of the mountain. If there is basically no difference in vegetation on both sides of the mountain, what does it mean?

5 The Hawaiian Islands, before the arrival of Austronesian languages, were home to a large number of birds, whose nests were built on land. After the arrival of humans, there were mass extinctions. The ancestors of the Hawaiian goose were the Canadian goose, which was blown to Hawaii by the wind during migration. Birds usually migrate long distances and reach the top of the troposphere. The troposphere is 8 km in the polar region and 13,000 km in the equatorial region. That's why these birds are blown off the rails.

6 World War I, the German company Krupp created the "Paris Cannon" with a range of 120 km, and shells could reach an altitude of 32 km. Why does the cannon have such a long range?

Water:

There is pressure in the atmosphere, and so does water. However, the thinning of the atmosphere is uneven, and the total weight of the atmosphere above 10 kilometers accounts for only a quarter of the total weight of the atmosphere. The atmosphere itself is very lightweight, and in the end 100 kilometers thick atmosphere and 10 meters thick water have the same effect.

How do you measure the difference between water and air in terms of manufacturing pressure? We introduce density, which is the weight in the same volume. When using density, it is common to have a volume at a specific value. For example, 1 cubic meter is a square with a side length and height of 1 meter. Discuss the weight of 1 cubic meter of air and water, and this weight value is the density of air and water. The density of water is 1,000 kilograms for 1 cubic meter, and the density of the densest air in the atmosphere is 12 kilograms for 1 cubic meter. Because the density of water is much greater than that of air, and the atmosphere is not uniform, in the end 10 meters of water is equivalent to 100 kilometers of atmosphere.

The deepest part of the ocean is the Mariana Trench, which reaches more than 10 kilometers, and the effect of this pressure is not comparable to the effect of 10 kilometers of the atmosphere, which is now 1,000 times the atmospheric pressure. Astronauts in space need to balance 1 atmosphere. At the deepest point of the seabed, there is a balance of 1,000 atmospheres. So exploring the ocean is more difficult than space.

In the pool or in the river, you will feel lighter and less need leg strength support. What's going on here?

Observe the two figures on the left and right above. The cyan part on the left is water, and the green cross part is also water. The cyan part on the right is water, and the orange cross part is an object. The green and orange parts of the left and right images have exactly the same shape. Let's start with the image on the left. The water in the cyan part remains in shape because the green part is filled with water. If the green part of the water disappears, the shape of the water in the cyan part will change, and the water surface will be lowered. Looking at the water in the cyan part of the image on the left and right, there is no difference in the shape of the two parts of water, which means that the orange part of the object in the right image has the same effect on the cyan part of the water as the green part of the water on the left part of the water. Otherwise, there will be a difference in the cyan part on both sides. Now look at the image on the left, the green part of the water remains in the middle position and does not move. According to Newton's observations, this part of the water is supported, otherwise it will sink to the bottom. And the force of this support is exactly the same as the weight of the water in the green part. For the figure on the right, the cyan part does not know what the orange part is, but only knows that the effect of the orange part on the cyan part is equivalent to the effect of the orange part being filled with water, so the effect of the cyan part on the orange part is to produce a supporting force, which is equal to the weight of water in the orange part. Now this support force is named buoyancy. Now that we change all the water to gasoline, alcohol, or some other liquid, the above analysis remains the same. That is, the magnitude of buoyancy (or support) is equal to the volume of liquid occupied by an item

(This chapter is not finished, please turn the page) corresponding to the weight of the liquid. Archimedes is the earliest in the record.

The main component of our body is water, which is not easily compressed. If it's air, we can't dive. Even if we use some means to dive and dive to 10 meters, we will be crushed to half of our original volume.

Under normal circumstances, air is everywhere, and if you want to eliminate atmospheric pressure, you need to eliminate it completely. There is no gas, liquid, or other substance in a certain space, which we call a vacuum. For example, in space, it can be called a vacuum, and this vacuum is cleaner than the vacuum we create on the ground. The 100-kilometer-thick atmospheric equivalent is a 10-meter-high column of water, which is also equivalent to a 076-meter-high column of mercury. Because the density of mercury is 10/076 = 134 times that of water. As shown in the picture on the right, take a 1 meter long glass thick tube, one end of which is closed and the other end is open. Fill with mercury, plug the opening and put it into the mercury pool, release the plug, the orange part of the mercury pool surface bears atmospheric pressure, and the pink part bears the mercury pressure in the glass tube, when the two are the same, the mercury surface remains balanced. That is, the atmosphere at a height of 100 kilometers and the column of mercury at a height of 076 meters produce the same pressure. The part of the glass tube that exceeds 076 meters is the vacuum. There is actually a small amount of mercury vapor in it.

Ponder:

1 Now we replace the liquid with a gas, that is, does the air have buoyancy on the object in it?

2 Birds fly in the air and airplanes fly in the air, is it buoyancy that plays a role?

3. In the early years, manual pumping machines could be seen in rural areas, and some water should be poured into the rubber piston on it to seal it before use. So how many meters can the well water be pumped high?

4 people squatted for a long time and suddenly stood up, why did they get black and dizzy in front of their eyes?

5 to question 4, giraffe is 55 meters tall, what situation may pose a threat to its life?

Stress and buoyancy that arise in life:

1 water system, fountain

2. Flush toilet tank (buoyancy combined with lever to achieve automatic predestined water measurement, water pressure to achieve flushing)

3. Pumps

4. Soup of rice noodles across the bridge

5. Blood pressure monitor

6 hole lights

7 Cruises in the park

On Earth, any object is attracted by the Earth, so gravity is omnipresent. We live in the atmosphere, and the objects around us are subject to the buoyancy of the atmosphere. However, the air density is small, the buoyancy is very small, and in most cases it can be ignored. When some objects are large, buoyancy is not negligible.

Ancient Applications:

Boats are tools that influence the course of human civilization. Roads and transportation have always been the main factors restricting the exchange and development of civilizations. Before the development of modern machinery and chemical industry, water transportation was the most cost-effective means of transportation. 4,000 years ago, the ancient Greeks sailed ships and colonized the Mediterranean and Black Sea regions. Austronesian people who conquered the Indian and Pacific oceans also had to use boats. In places where there is a high demand for transportation, humans dig canals to communicate with waterways. For example, the Ling Canal, the Beijing-Hangzhou Grand Canal, the Kiel Canal, the Panama Canal, and the Suez Canal. The ship's float depends on buoyancy, while the forward power can be human power (the Greek trireme), wind power (Chinese hard sails, Arabian soft sails), mechanical power (steam engine Fulton), and nuclear power (Nautilus).

Modern applications:

1 balloon, including hot air balloon and hydrogen balloon. You can take people into the sky and see the world from a new perspective. In the days when the aircraft was immature, the balloon could be used for reconnaissance (artillery calibration), air transport (Count Zeppelin). In the days when space technology was not mature, balloons could reach the top of the stratosphere for astronomical observations.

2. Dig up the oil and inject high-pressure hot water into the oil well, which can make the oil spray out automatically. Like an artesian well, the internal pressure itself is high enough to overcome the corresponding pressure of the liquid rising to the surface. Extracting water in deep wells relies on the strong pressure of the water pump to overcome the gravity of the water itself. The method of mining water-soluble ore (rock salt) or hot melt ore (sulfur) is similar.

Observe:

1 Cigarettes are harmful to the body, but many people smoke them. Observe the process of smoking, see how the smoke enters the body, and pay attention to standing upwind to avoid being harmed.

2. In the infusion system of the hospital, the general medicine bottle is hung at a relatively high position, the middle is a buffer zone to regulate the flow, and the lowest position is the infusion needle, which is pierced into the blood vessel. When the height of the buffer is inadvertently lowered, blood is found to flow backwards into the infusion tube.

3. Water cannon pumping and hospital blood pumping are all using the principle of vacuum. Observe the manufacturing process of these vacuums.

(End of chapter)