Junior high school physics: What do you know about the phenomenon of material changes in life?

Junior high school physics: What do you know about the phenomenon of material changes in life?

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1. Read proverb and explain the change of material changes

1. Snow falls into the mountains, frost drops the plain.

Answer: In the snowy days, the temperature of the mountain is lower than the flat on the bottom of the mountain, and the snow from the mountains is not easy to melt. Therefore, the same snow, there are more high mountains than flat. Frost is the result of condensation on the water vapor on the ground. The water vapor on the surface of the mountain on the surface of the mountain is more than the mountains.

2. Sweat water tanks, don't need to carry a burden (water tank wears skirts, it will rain in the sky).

Answer: Due to the evaporation of the water in the cylinder, the temperature below the water surface is lower than the temperature of the air. The water vapor in the air encounters a liquefied phenomenon on the outer surface of a low temperature cylinder, and the water droplets are attached to the outside of the water tank. Due to the small water vapor content in the air on a sunny day, although the water vapor will also liquefy the surface outside the water tank, the trace liquefaction quickly evaporates again, and water drops cannot be formed. If the air is humid, the water evaporates very slowly. The liquefaction on the outside of the water tank is greater than vaporization, and there will be water drops. The content of water vapor in the air is large, and the possibility of rainfall is high. Of course, there is no need to pick water.

3. Do not sound boiling water, and the sound is not open.

Answer: Because the bubbles in the water rise when the water is boiled, the faster the bubbles will rise. The louder the sound of the air bubble, the rising the bubbles is related to the temperature difference between the water and the water on the bottom of the kettle. quick. When boiling water, the temperature of the water at the bottom of the pot is higher, the surface of the surface is low, the temperature difference is large, and the bubbles rise quickly, so "noise water does not open." When the water is boiling, the water at the bottom of the pot is basically equal to the water on the surface, and the bubbles in the water rise slowly, so "boiling water does not sound".

4. Frozen three feet, not a day cold.

Answer: Frozen is the solidification of water. The temperature of the water is abnormal expansion between 0 ° C and 4 ° C, that is, heat shrinking and swelling. In winter, when the temperature drops, the temperature of the upper river water is low and the density is large, so it is necessary to sink. The temperature of the water at the bottom of the river is high and the density is small. When the temperature of the entire river drops to 4 ° C, the convection stops. When the temperature continues to decline, the temperature of the upper river water continues to decline, and the temperature of the bottom of the river still remains 4 ° C. When the temperature of the upper layer drops to 0 ° C and continues to heat up, the river surface starts to freeze. Since then, because water and ice are hot and bad conductors, smooth and bright ice surface can prevent radiation, so the three methods of heat transfer are not easy to perform. The ice requires a long time, so there is a saying that "frozen three feet, not a day's cold".

5. It is not cold at snow and cold snow.

Answer: Snow is formed by the solidification of water vapor in the air or small water droplets. Because the coagulation and solidification are the heat control process, it feels not cold, and the snow melting is the process of heat absorption, so it feels cold.

6. Cold before frost, cold after snow.

Answer: The formation of frost is the process of condensation, and Ninghua is a heat -heat process, so the temperature before the frost should be very low, and the water vapor in the air can heat up and condense the cream. Or a large amount of heat should be absorbed during the sublimation process, so the outdoor temperature will be very low after snowing.

Second, thermal phenomenon in the kitchen

1. After the water in the kettle is boiled, how is the "white qi" seen at the pot of the pot?

Answer: Water vapor is formed by cold liquefaction.

2. After the water in the winter kettle is boiled, why can you see "white gas" at a certain distance at the pot mouth, but the place that is close to the pot mouth does not see "white gas"?

Answer: "White Qi" is formed by cold liquefaction when water vapor is cold. The temperature near the pot mouth is high, and the water vapor cannot be liquefied, so it cannot be seen. Small water droplets, that is, the "white qi" that I see.

3. Why is the pot burning with the iron pot welded in the tin, and it is not broken when the pot is burned.

Answer: When boiling water, keep the boiling point unchanged after boiling. Under the atmosphere of 1 standard, it can only reach 100 ° C. The melting point of the tin is 213.9 ° C. At that time, the temperature of the pot continued to rise, and it quickly reached the melting point of the tin. The weld was melted and the pot burned out.

4. When you get a little cold water with the ripe buns that have just come out, why don't you feel hot?

Answer: When the cold water encounters hot steamed buns, it quickly vaporizes, forming a layer of water vapor between the hands and the steamed buns, and the water vapor is a bad conductor of heat.

5. The dumplings will not become yellow zoom in the water, no matter how you cook it, why will it be frying in the oil to become yellow zoom?

Answer: The boiling point of oil is much higher than the boiling point of water.

6. The water will explode in a hot oil pan, but the oil falls into the hot water pot but it will not explode. Why?

Answer: When the water falls in the hot oil pan, the temperature in the pot has already exceeded the boiling point of the water. The water is immediately vaporized into water vapor, the volume is expanded rapidly, and the water is heavier than the oil. Caused a severe vibration, made a sound and explosion, and splashed oil flowers; when the oil fell into the boiling water pot, the temperature of the boiling water in the pot was lower than the boiling point of the oil, and the oil drifted on the water. There will be no explosion.

7. 100 ° C water vapor is scalded than 100 ° C. Why?

Answer: The water vapor at 100 ° C is scalded, because the water vapor at 100 ° C has a liquefied and heat -draining process than the water at 100 ° C. 8. After scald, it is better to use 0 ℃ water or at 0 ℃. Why?

Answer: The cold compress of 0 ° C is better, because the ice at 0 ° C has a melting process than the water of 0 ° C.

9. The oil boiled oil when fried food is often more serious than the boiled water splashing to the body. Why?

Answer: The burning oil is more serious, because the boiling point of the oil is much higher than the boiling point of the water.

10. A drop of water of the same size, dripped into the hot pot and dripped into the hot red pot. It turned out that the water dripped into a hot pot with a lower temperature, but the water was dried first. Why?

答：锅热得发红温度过高，滴入的水迅速蒸发，水蒸气将水滴托起，使水滴与锅接触的面积减小，蒸发减慢；而滴入热锅里的水在流动， The surface area of ​​contact with the pot increases and evaporates, so it is done first.

11. "Yang Tangzhi Boiling" refers to the soup burned in the pot and pour it back. Please explain the reasons for the physical knowledge you have learned.

Answer: "Yang Tang stops boiling" refers to the soup burned in the pot and pour it back. It does not stop heating, but temporarily stops the boiling; Stopping heating is to stop boiling.

Third, the material change in poetry

1. Shanglian "Ice water in the cup, the ice temperature of the water is not descending"; Xialian: "Water ice in the plate, the ice water temperature does not rise", what kind of material changes contain, and why is there such a phenomenon?

Answer: "Ice water in the cup, the ice temperature of the water is not descending" -Coloniating, heat out of the heat when solidification, and the temperature remains unchanged; When the heat is absorbed, the temperature remains unchanged.

2. Lushan is famous for its beautiful scenery. The Tang Dynasty poet Li Bai wrote in the poem "Wang Lushan Waterfall", "Rizhao incense furnace has purple smoke, and watch the waterfall hanging in the front of the front. Nine days. " Please explain the formation of "smoke" from the perspective of physics.

Answer: "Smoke" is a small droplet formed by water vapor liquefaction.

Fourth, material changes in nature

Please use the knowledge you learned to explain how the following natural phenomena are formed, and explain whether it absorbs heat or heat up.

1. Rain: Water vapor is formed by cold liquefaction.

2. Dew: Water vapor encounters cold liquefaction.

3. Mist: Water vapor is formed by cold liquefaction.

4. Hail: Water vapor encounters cold liquefaction to form small water droplets. Small water beads encounter cold coagulation (heat -heating) into small ice hockey. The small ice hockey is melted into water and then combined with small ice hockey.

5. Ice: Water solidification and insulation formation.

6. Snow: The water vapor directly condenses the formation of heat.

7. Frost: The water vapor directly condenses the formation of heat.

8. Window flowers (occurring on the surface of the window): The water vapor directly condenses the heat and heats up.

9. Misty: The water vapor directly condenses (solidification) is formed.

5. Explain the reasons for the formation of "white qi" in the following phenomena

1. "White Qi" exhaled in the mouth of the people's mouth: The water vapor liquefied in the population of the population forms a small water ball.

2. "White Qi" emerging from the kettle mouth: The water vapor in the kettle is liquefied to form a small water droplet.

3. When opening the beer bottle, the "white gas" appeared at the mouth of the bottle: the water vapor in the air forms a small water bead.

4. When opening the refrigerator door, the "white gas" appears near the refrigerator door: water vapor in the air forms small water droplets.

5. The "white gas" around the cream from the refrigerator: The water vapor in the air forms a small water droplet.

6. The heat phenomenon around you

1. Frozen clothes can also be dried in an environment below 0 ° C: sublimation (heat absorption)

2. In the wind, when swimming, it will feel particularly cold after swimming: vaporization (heat absorption)

3. In winter, when the students wearing glasses walk from the warm room to the cold outdoor, small water droplets will appear on the lens: water vapor encounters cold liquefaction (inspiration)

4. When swimming in summer, I do n’t feel cold in the water, but feel cold after going ashore: evaporate (heat absorption)

5. The inner wall of the long -term light bulb turns black: tungsten wire is sublimated (heat absorption) and then condensed (indoor)

6. Use a long time of light bulb filament to thinner: tungsten wire sublimation (heat absorption)

7. The eggs taken out of the refrigerator are wet first and then dried: the water vapor in the air encounters cold liquefaction (heat -heating) into small water droplets, and then vaporizes (heat absorption) into water vapor.

8. After taking a hot bath in the bathroom, the glass mirror of the indoor becomes blurred. After a period of time, the mirror surface becomes clear again: the water vapor in the air is cold liquefaction (drain) into a small water droplet , Then vaporize (heat -absorbing) into water vapor.

9. The camphor ball in the closet will become smaller and smaller: sublimation (heat absorption)

10. Wipe alcohol to feel cool on the skin: evaporate (heat absorption)

11. Dentist uses a small mirror used to observe the patient's teeth. It should be placed on the fire to bake it into the patient's mouth: in order to prevent the cold mirror from being placed in the population. Essence

12. Now there is a product called "solid fresh agent". It is placed in toilets, cars, and restaurants to effectively fresh air and prevent colds. hot)

13. In the summer, rural families without refrigerators, in order to prevent the meals from becoming the taste, often put the food into the washbasin, and then float the washbasin in the water cylinder: the water evaporates heat and heats the cooling effect.

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