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Air refers to the mixture of gases in the earth's atmosphere, for which air belongs to the mixture, which is mainly composed of nitrogen, oxygen, noble gases (helium, neon, argon, krypton, xenon, radon), carbon dioxide and other substances (such as water vapor, impurities, etc.). Among them, the volume fraction of nitrogen is about 78%, the volume fraction of oxygen is about 21%, the volume fraction of rare gases (helium, neon, argon, krypton, xenon, radon) is about, the volume fraction of carbon dioxide is about, and the volume fraction of other substances (such as water vapor, impurities, etc.) is about. The composition of air is not fixed, and as the altitude changes, the air pressure changes, and the proportion of air composition also changes.
But for a long time, it was believed that air was a single substance, until later the French scientist Lavoisier first came to the conclusion that air is composed of oxygen and nitrogen through experiments. At the end of the 19th century, scientists discovered through a large number of experiments that there were rare gases such as helium, argon, and xenon in the air.
The second question is not very clear, but if I were to contact your first question, I guess you are confirming the existence of air, or the density of air.
The above answer is from Encyclopedia.
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There is such an experiment in the first volume of science in the fourth grade of the Sujiao version, I think: 1. The purpose of the experiment is to test whether the remaining gas supports combustion. 2. If it supports combustion, it will definitely consume the gas inside, and the water surface in the bottle will rise; If burning is not supported, the water surface in the bottle remains the same.
3. Therefore, if it is not added to the same height, you cannot know whether the water surface in the bottle has changed.
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Because the air in the bottle is compressed back to the cover, the air pressure is greater than the atmospheric pressure outside, so the water surface in the bottle cannot reach the high dispersion degree outside, which means that the air inside is compressed and leaked, so the water cannot be squeezed in.
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The air inside the bottle on the right expands by heat, so the pressure on the water surface inside the bottle drops. At the same time, the boiling point of the water rises due to the increase in the pressure inside the bottle, and when the water in the sink boils, the water in the bottle on the right does not reach the boiling point, and it cannot boil because it can no longer absorb heat. Hope to adopt.
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When the water is heated, it produces water vapor, and the air pressure of the bottle on the right increases, and the water level drops. An increase in air pressure will increase the boiling point of water, and the air pressure outside the bottle will not change, so the outside water will boil first.
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Water boiling is the process of vaporization, and the water must continue to absorb heat to boil after reaching 100 degrees, while only the water at the bottom of the beaker can continue to absorb heat after reaching 100 degrees, so the water in bottle A will not boil. As for acetylene, first of all, the air pressure in the bottle is higher than that of the outside, so the boiling point of the water inside is higher than that of the outside, and secondly, it should be the previous reason. D should be chosen
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Water vapor is also one of the air components; Carbon dioxide can also be combined with water to form carbonic acid.
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If the weight of the water in the bottle is g, the area of the bottle mouth is s, then the pressure of the cavity calendar is g s, and the pressure of the water in the sink on the bottle mouth can also be calculated.
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The clump of water in the bottle must not be more than 10m high, right? The water in the bottle falls downward due to gravity, so the space in the bottle will become larger, but the air is constant, so the pressure becomes smaller. The outside atmospheric pressure is greater than the atmospheric pressure inside the bottle, so the water is jacked up and does not flow out.
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The air pressure in the bottle cancels out the atmospheric pressure outside, causing the water in the bottle to be incapable of being pressed to the outside world.
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The atmospheric pressure in the bottle is smaller than that of the outside world, so the atmospheric pressure from the outside presses the water up.
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1) The red phosphorus was insufficient, and the oxygen was not consumed by the whole jujube rolling bucket, so the result was small; Opening the water stop clamp before cooling down is also equivalent to the oxygen is not fully consumed.
2) The air tightness of the device is not good, and the grinding gas of the oxygen bench in the device is consumed, but there is gas entering the device, so it is equivalent to that there is still oxygen that is not consumed, so the result is small;
3) Open the spring clamp before cooling to room temperature, so that the volume of water entering the bottle is reduced, so the answer is: 1) the red phosphorus is insufficient, and the oxygen is not fully consumed;
2) The sealing of the device is not good;
3) Open the spring clamp before it has cooled to room temperature
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The water inside the bottle will flow out until the water surface inside and outside the bottle is level. Because the bottom of the bottle is opened, the air reaches the water surface at the bottom of the bottle, at this time, consider the pressure of the water at a certain point on the bottle mouth, first, the pressure generated by the gravity of the water column in the bottle = PGH. Second, the pressure of the air passing through the sink on the water inside the bottle, and third, the pressure of the air through the hole in the bottom of the bottle on the water.
The second and third are exactly the same because the pressure is the same as the atmospheric pressure. So the pressure on the water is the pressure generated by gravity, and in the direction of downward, the water will flow into the sink until the water surface inside and outside the bottle are level. At this time, the height of the water column is h=0, so PGH=0, the pressure disappears, the water stops flowing outward, and the water surface inside and outside the bottle is level.
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There will be no change in the water in the bottle, because the air pressure inside the bottle is 0, and the outside is one atmosphere, and the atmospheric pressure holds up the water, so it will not flow out.
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The water will flow down until all the water in the cup flows into the sink, because there is no atmospheric pressure difference between the water in the cup and the water in the cup, and the water will flow naturally down because there is no force to balance gravity.
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The water will flow out until the water in the bottle is level with the water in the sink.
Same reason as above.
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