1. Concept: The pressure of the atmosphere on the object immersed in it is called atmospheric pressure, which is generally expressed by p0. Note: There is a difference between "atmospheric pressure" and "atmospheric pressure" (or partial pressure). For example, the air pressure in a pressure cooker refers to the pressure of some gases. The pressure cooker is called atmospheric pressure outside. 2. Reason: Because air is gravity and has fluidity. 3. The existence of atmospheric pressure-the experiment proves that it is a famous experiment in history-the Madeborg Hemisphere Experiment. Small experiments-the experiment of covering a cup, the experiment of swallowing eggs in a bottle, and the simulation experiment in a leather cup in Madeborg. 4. Experimental measurement of atmospheric pressure: Torricelli experiment. (1) Experimental process: A glass tube with a length of about 1m and a closed end is filled with mercury, and the nozzle is blocked, and then the mercury level in the tube drops a little, but it does not drop. At this time, the height difference of mercury column inside and outside the tube is about 760 mm. (2) Principle analysis: In the tube, the mercury level in the tube is about 760 mm.. Because the liquid does not move, the liquid sheet is subjected to a top-down pressure balance, that is, the upward atmospheric pressure = the pressure generated by the mercury column. (3) Conclusion: Atmospheric pressure P0 = 760mmhg = 76cmhg =1.01*105pa (its value changes with the change of external atmospheric pressure) (4) Description: Before the experiment, a mercury is poured into the glass tube, and if it is not filled, the measurement result will be very small. B. If mercury is replaced by water in this experiment, the length of the glass tube needs to be 10.3 m C, and the glass tube needs to be slightly raised or lowered. If the height difference between the inside and outside of the tube is constant, the glass tube will tilt, the height will be constant and the length will become longer. D if the outside atmospheric pressure is H cmHg, please write the following information. Pressure of sealing gas (the liquid in the tube is mercury). h cmhg(h+h)cmhg(h-h)cmhg(h-h)cmhg(h+h)cmhg(h-h)cmhg(h-h)cmhg(h-h)。 CmHg E standard atmospheric pressure: the atmospheric pressure supporting 76cm Hg is called standard atmospheric pressure. 1 standard atmospheric pressure = 760mmhg = 76cmhg = 1 .01*105pa2 standard atmospheric pressure =2.02* 105Pa, which can support the water column height of about 20.6m 5 and atmospheric pressure: (/kloc-) Atmospheric pressure decreases with the increase of altitude, and its value is related to the changes of location, weather and season. Generally speaking, the air pressure in sunny days is higher than that in cloudy days, and the air pressure in winter is higher than that in summer. (2) Changes in atmospheric pressure. For every rise of 10 meter, the atmospheric pressure drops by about 100 Pa 6. Measuring tool: Definition: The instrument for measuring atmospheric pressure is called barometer. Classification: Mercury barometer and aneroid barometer Description: If the mercury barometer is tilted, the measurement result will become larger. The scale on the dial of the aneroid barometer is changed to height. This aneroid barometer becomes an altimeter for mountain climbing. 7. Uses: piston pump and centrifugal pump. 8. Boiling point and pressure: Content: The boiling point of all liquids decreases when the air pressure decreases and increases when the air pressure increases. Application: pressure cooker, removing water from sugar juice. 9. Volume and pressure: Content: The smaller the volume, the greater the pressure. Answer: ① use a plastic straw to suck drinks from the bottle; ② Draw water for pens; ③ Use clothes hangers with suction cups; ④ People do inspiratory exercise.
2. Atmospheric pressure knowledge
Atmospheric pressure [knowledge]
Q: What factors are related to the change of atmospheric pressure? How did it change?
A: The change of atmospheric pressure is related to altitude. Atmospheric pressure is produced by gravity in the atmosphere. The higher the ground, the thinner the atmosphere, and the smaller the atmospheric pressure should be. However, because the air density related to the gravity received by the atmosphere varies unevenly with height, the atmospheric pressure decreases unevenly with height.
The change of atmospheric pressure is also related to the weather. At different times, the atmospheric pressure in the same place is not exactly the same. We know that the density of water vapor is less than that of air. When there is more water vapor in the air, the air density will become smaller and the atmospheric pressure will also decrease. Generally speaking, the air pressure in rainy days is smaller than that in sunny days, and it is found that the sudden drop of air pressure in sunny days is a precursor to rain; However, after several days of continuous rain, it is found that the air pressure has become larger, and it can be expected that it will clear up soon. In addition, the change of atmospheric pressure is also related to temperature. Because the air density becomes smaller at high temperature, the atmospheric pressure is smaller at high temperature than at low temperature.
Q: What is the standard atmospheric pressure? How is its value obtained?
A: Atmospheric pressure is not fixed. In order to compare atmospheric pressure, at the 10th International Metrology Conference in 1954, scientists stipulated a "standard" for atmospheric pressure: at the sea level of latitude 45 and the temperature of 0℃, the pressure generated by a mercury column with a height of 760mm is called the standard atmospheric pressure. Since it is a "standard", we should pay attention to the accuracy of each physical quantity according to the formula of liquid pressure. According to relevant data, the density of mercury at 0℃ is 13.595* 103 kg/m3, and the g value at sea level at latitude 45 is 9.80672 N/kg. Therefore, it can be concluded that the pressure generated by a 760mm high mercury column is
P mercury = ρ mercury gh
=13.595 *103kg/m3 * 9.80672nn/kg * 0.76m.
= 1.0 1325 * 105 Pa。
This is the value of 1 standard atmospheric pressure.
3. It is better to have a question to find out the detailed knowledge of atmospheric pressure in junior high school physics.
1. Also known as "atmospheric pressure".
One of the important meteorological elements. Pressure caused by the weight of the atmosphere around the earth.
Its size is related to conditions such as height and temperature. It generally decreases with the increase of height.
For example, the atmospheric pressure on high mountains is much smaller than that on the ground. In the horizontal direction, the difference of atmospheric pressure leads to the flow of air.
2. Pressure unit. Short for "standard atmospheric pressure".
Actually, it's 760 torr (mmHg). For the convenience of engineering, 1 kg per square centimeter (=735.6 Torr) is defined as the unit of pressure, which is called "engineering atmospheric pressure" or "atmospheric pressure".
The earth is surrounded by thick air, which is called the atmosphere. Air can flow freely like water, and it is also influenced by gravity.
So there is pressure in all directions in the air, and this pressure is called atmospheric pressure. 1654, Gehrig made a famous experiment in Madeborg, Germany, which strongly proved the existence of atmospheric pressure and made people have a deep understanding of atmospheric pressure, but people still don't know how big it is.
1 1 years later, Italian scientist Torricelli filled an 80 cm long thin glass tube with mercury and put it in a sink filled with mercury. He found that the mercury in the glass tube dropped by about 4 cm, and then stopped falling. There is no air in this 4 cm space, it is a vacuum.
Torricelli deduced from this that the pressure of the atmosphere is equal to the length of the mercury column. Scientists accurately calculated the atmospheric pressure as1.03 *105pa1standard atmospheric pressure = 760mmhg = 76cmhg =1.013 *10, and quintic Pascal = 650.
With the development of science and technology, the standard atmospheric pressure and its changes have changed many times. At first, the atmospheric pressure at sea level of 0℃ and latitude of 45 in sunny days was defined as standard atmospheric pressure, which was equivalent to about 76 cm Hg.
Later, it was found that the air pressure value under this condition was unstable and changed under the influence of wind, temperature and other conditions. Therefore, the height of 76 cm Hg is defined as the standard atmospheric pressure.
However, it was later found that the pressure value of 76 cm Hg was also unstable, and the density of mercury changed under the influence of temperature. The value of g also varies with latitude. An instrument for measuring atmospheric pressure is called a barometer.
In order to ensure that the standard atmospheric pressure is a constant value, 1954, the resolution of the 10th International Metrology Conference stipulates that the standard atmospheric pressure value is 1 standard atmospheric pressure =1kloc-0/325 Newton/square meter atmospheric pressure. The relationship between temperature, humidity and atmospheric pressure tells us: "The change of atmospheric pressure is closely related to the weather. Generally speaking, the air pressure in sunny days is higher than that in cloudy days, and the air pressure in winter is higher than that in summer. " It is often difficult for teachers to explain this narrative clearly. In my opinion, this problem can be attributed to the relationship between temperature, humidity and atmospheric pressure. Let's talk about my own preliminary understanding. What we usually call the atmosphere is the whole air layer around the earth. Besides nitrogen, oxygen and carbon dioxide, it also contains water vapor and dust. We call air with less steam (i.e. low humidity) dry air and air with more steam (i.e. high humidity) wet air. Don't think that "dry" things must be lighter than "wet" things. In fact, the molecular weight of dry air is 28.966, while that of water vapor is 18.066. The density of dry air is also greater than that of water vapor. The density of water vapor is only about 62% of that of dry air. It should be said that because the atmosphere is in the open space around the earth, there is no specific boundary to limit its movement range, which makes it different from the gas in a closed container. For a closed container filled with air, as long as the gas in the container is not saturated, when we input water vapor into the container, the pressure of the gas will inevitably increase, but the atmosphere will not. When the atmospheric humidity in a certain area increases due to natural factors or human factors, the molecules of "wet air" (including air molecules and water vapor molecules) in this area will inevitably spread to the surrounding areas. In this way, the content of "dry air" in the atmosphere in this area will be less than that in the surrounding areas. The water vapor content is higher than that in surrounding areas. This is just like when cottonseed is mixed with soybeans, the density of the mixture is lower than that of soybeans, so the density of wet air in this area is lower than that of dry air in other areas. In this way, the weight of the air column per unit area in this area is lower than that of the same air column in other dry air areas, which tells us that with the increase of air humidity, the atmospheric pressure decreases. As far as cloudy days and sunny days are concerned, the air humidity on cloudy days is actually higher than that on sunny days, so the air pressure on cloudy days is lower than that on sunny days. We know that the "collision" of gas molecules is the fundamental cause of gas pressure. Therefore, it can also explain the problem that atmospheric pressure changes with air humidity. According to the basic theory of gas molecular motion, the average velocity of gas molecules: the average momentum of gas molecules (only considering its size) can be seen from this. The average momentum of gas molecules with large average mass is also large (some literature ① says: "The average speed of dry air is also greater than that of humid air", which is incorrect). For dry air and wet air under the same conditions, the molecular density and average mass of gas molecules in dry air are greater than those in wet air, and the average momentum of dry air molecules is also greater than that in wet air. Therefore, the pressure of dry air with low humidity is greater than that of humid air with high humidity. When we heat a closed container filled with air, its pressure will definitely increase. For the atmosphere, things are different. When the atmospheric temperature in a certain area rises due to some factors, it will inevitably lead to the expansion of air volume, and air molecules will inevitably spread around. When the temperature is high, gas molecules will certainly move faster. This will become a factor to promote the increase of pressure. On the other hand, with the increase of temperature, gas molecules will diffuse around, and the number of gas molecules in this area will decrease, thus forming a factor to promote pressure reduction. The actual situation is the result of the interaction of the above two opposing factors. As for which of these two factors plays a major role, we might as well look at the actual situation of air pressure changing with temperature on the mainland and the ocean. We say that the temperature ratio of the mainland in summer.
4. Physical stress knowledge points in the second day of junior high school
Pressure 1. Pressure P: The pressure per unit area of an object is called pressure.
Pressure F: the force acting vertically on the surface of an object, in N ... The function of pressure is expressed by pressure, which is related to the pressure and the stressed area.
Pressure unit: n/m2; Scientific name: Pascal (Pa) formula: F=PS S: stress area, the common part of contact between two objects; Unit: square meters. Methods of changing pressure: ① reducing pressure or increasing stress area can reduce pressure; ② Increasing the pressure or decreasing the stress area can increase the pressure.
1. liquid internal pressure: measure the liquid internal pressure: use a liquid manometer (u-tube manometer). Reason: Because the liquid has gravity, it exerts pressure on the bottom of the container; Due to the fluidity of the liquid, pressure is generated on the wall of the device.
Law: ① At the same depth, the pressure in all directions is equal; ② The greater the depth, the greater the pressure; ③ Different liquids at the same depth, the higher the liquid density, the greater the pressure. [Depth h, the vertical height from the liquid surface to a certain point of the liquid.
] formula: p = p = P=ρgh h: unit: meter; ρ: kg/m3; G=9.8 N/kg. 13. Atmospheric pressure: gravity produces atmospheric pressure, which proves the existence of atmospheric pressure and is very large. It was the Madeborg Hemisphere Experiment and Torricelli (an Italian scientist) who measured the atmospheric pressure.
After the Torricelli tube is tilted, the height of the mercury column remains unchanged and the length becomes longer. 1 standard atmospheric pressure =76 cm Hg height =1.01*105pa =10.336mh. Instruments for measuring atmospheric pressure: barometer (mercury barometer, box barometer).
The law of atmospheric pressure changing with altitude: the higher the altitude, the smaller the pressure, that is, the lower the boiling point with the elevation.
5. What is the knowledge of pneumatic system?
On the meteorological map, the air mass marked with the word "high" has a higher ground pressure than the surrounding air mass. Low-pressure air masses exist in the cracks where air masses rub and mix with each other (remember, "high" and "low" are relative words similar to "hot" and "cold"). Generally speaking, air masses are not easy to mix with each other. When air masses with great density differences meet, the low pressure area between them usually develops into an extremely unstable area, which makes the transition between air masses become intense and forms a narrow rain belt, which is called the front.
High pressure and low pressure are controlled by high-altitude jet, and the formation of jet begins with high pressure and low pressure. On the surface of the earth, due to the Coriolis effect, the air moves relatively slowly and moves in a circle.
Huge semi-permanent low-pressure air mass and high-pressure air mass generate and guide the moving air pressure system. In a certain area, their influence on the weather is dominant, and their position and intensity change with the seasons. These air pressure systems were located in July, which was the rainy season in India. However, in June+10, 5438, a low-pressure area named "Aleutian" moved along the coast of Alaska and disappeared in summer, which triggered the Asian storm again and moved it to the Pacific Ocean, affecting North America. Similarly, the storm in North America moved and strengthened over the subtropical Atlantic Ocean, forming a low pressure in Iceland (Icelandic low pressure); Re-enter Europe. In this case, all the physical factors that affect the weather-water vapor, air pressure and air mass-are playing a role at the same time, causing great influence.
6. A little knowledge of physics
I'm sorry.
It looks like that. .. it's really hard.
.. embarrassed, embarrassed. In addition, contact in advance will cultivate your interest in learning ... these are junior high school students.
You will see. .. 1. A moving bicycle will stop after braking. What is the reason why the bike stopped? Answer: The friction between the moving bicycle wheel and the ground is rolling friction. After braking, the wheel is not easy to rotate, and the friction between the wheel and the ground becomes sliding. Sliding friction is much greater than rolling friction, so the bike will stop.
2, knowledge points: when measuring the length, we must estimate the next smallest scale. 3. Knowledge point: The height of the mercury column is the vertical distance from the upper surface of the mercury column in the glass tube to the mercury surface in the mercury tank. Therefore, when the glass tube is tilted, the length of the mercury column becomes larger, but the height remains the same.
4. An object moves in a straight line at a uniform speed on two horizontal planes with the same length but different roughness. The work done on the smooth section is W 1, and the work done on the rough section is W2. Find the relationship between W 1 and W2. Answer: W 1=W2 5. A small ball was placed on the smooth floor of the carriage. When the frame is subjected to a horizontal force F to the right, the frame accelerates from standstill. What is the movement of the ball on the ground during the movement? Answer: Still.
6. Two solid cylinders A and B are placed on the horizontal ground, and their pressure on the ground is equal (the bottom and height of A are smaller than that of B), so who has the greater density and gravity? Answer: A university. A small glass.
7. This scale measures the length of an object three times. 50CM, find the minimum scale value of this scale.
Answer: 0. 1CM 8. Knowledge point: evaporation only occurs on the surface of liquid, while boiling occurs both on the surface and inside. Evaporation is mild and boiling is intense. Evaporation can occur at any temperature, but boiling can only occur when it reaches a certain temperature. The temperature of evaporation itself and its surroundings decreases, and the boiling temperature remains unchanged. 9. Knowledge points: temperature-internal energy (certain) internal energy-temperature (not necessarily) internal energy-heat (not necessarily) internal energy (certain) temperature and heat are not necessarily 10. Knowledge points: Characteristics of power stroke: spark plug ignition, piston moving down, rotating shaft moving left, no air intake, no exhaust.
1 1, knowledge point: convex lens: when the object distance is within a focal length, the object distance becomes smaller, the image distance becomes smaller, and the image becomes smaller. When the object distance is greater than a focal length, the object distance increases, the image distance decreases and the image becomes smaller.
When the object distance is a focal length, no imaging is performed. 12. In the parallel circuit, as long as one more resistor is connected in parallel, the total resistance will decrease regardless of the size.
In series circuit, if a resistor is connected in series, regardless of its size, the total resistance will inevitably increase. 13. How to study the relationship between conductor resistance and conductor length with two resistance wires with the same length and different thickness? Answer: Use a resistance wire to fix one end of the wire, and the other end slides on the resistance wire to compare the resistance.
14, a person standing on a dry wooden bench, holding the live and zero wires in both hands, measuring his hands and skin with a pencil. The neon lights are shining, but this person is very nice. What is the reason? Answer: Someone has disconnected the zero line. 15. I saw fish flying in the sky and birds swimming in the water somewhere. What is the reason? Answer: Fish is a virtual image formed by light refraction, and birds are a real image formed by light reflection.
16. What sports can astronauts do under the condition of complete weightlessness? Answer: For example, exercise with a spring dynamometer. Running and pull-ups on the treadmill are not allowed.
17. Are the gravity of the car and the supporting force of the ground on the car interactive or balanced? Answer: balance force. 18, knowledge point: the connector is a container with only an upper opening and a connected bottom.
Principle: When there is only one liquid in the communication device and it does not flow, the liquid level of each container is horizontal. 19. When doing the Torricelli experiment, the measured atmospheric pressure is smaller than the true value. Why? A: There is a small amount of air mixed in the glass tube.
20. A container with a thick bottom and a thin top is filled with water. The pressure of water on the ground of the container is 15N. Then, put a wax block weighing 2N in the container, and the wax block will float, so that water will not overflow the container. What is the relationship between the pressure of container ground water and the size of 17N? Answer: greater than 17N. 2 1. When an ice cube is put into isothermal water, its gravity is greater than its buoyancy. How does the water level change when the ice melts completely? Answer: Up.
22. Knowledge point: Doing work must meet the requirements: a strong force acts on the object, and the object passes a distance along the direction of the force. 23. Someone wants to lift a 5N object1m. What did he do the least? 1, unarmed 2, movable pulley 3, inclined plane 4, crown block? Answer: unarmed.
24. What mechanical energy does a naturally elongated spring have? Answer: No. 25. Scene: Yunnan Crossing the Bridge Rice Noodles.
Find physical phenomena and explain them. Answer: 1 does not emit hot air: oil slows down the evaporation of water; 2 forming oil film: the density of oil is smaller than that of air.
3. The meat is cooked: there is heat transfer between the soup and the meat. 26. Knowledge point: Doing work and heat transfer are equivalent in increasing the internal energy of an object.
27. Xiaogang took a beautiful underwater photo with his camera. After the water was drained, Xiaogang did not move. Should he stretch the camera forward or backward? Answer: backward. 28. What happens when a fly stops in front of the camera lens to take pictures? Answer: There are no flies, but it will be darker.
29. Xiaogang wants to verify whether his rubber ball is elastic or Xiaoming's. Can he? Answer: If you drop two balls at the same height, the rebound force is high and the elasticity is good. 30. What is the difference between inserting an iron core and a steel core in an electrified bobbin? Answer: Iron can be demagnetized immediately after power failure, but steel can't.
3 1, electromagnetic waves are mainly used for? A: Disseminate information. 32. Does nuclear energy come from the sun? Answer: No.
A car (gasoline) and a tractor broke down on the expressway. After inspection, the battery is broken and cannot be started. At this time, someone asked, what car can run after pushing them? Answer: Tractor. 34. Knowledge points: The geomagnetic south pole is near the geographical north pole, and the geomagnetic north pole is near the geographical south pole.
35. A wooden block A floats on the water and an iron block B is placed on it. Both blocks of wood and iron are above the water. The volume of wood blocks immersed is V 1. Take the iron from A and put it in the water. The displacement of wood blocks and iron blocks is V2. It is known that V 1-V2=4 cubic decimeters, and the volume of A is 8 cubic decimeters. Answer: 40N 36. Pull an object with a bottom area of 200 square centimeters 100N on a horizontal plane. What is the resultant force on the object? What is the ground pressure? Answer: 0. 3000 pa.
37. Be a Conservative party member.
7. Physical tips
Question 1: Why did jiaozi sink when he was first poured into the pot?
* Question 2: Why does jiaozi float when cooking, and only jiaozi floats when cooking?
* Question 3: Why did jiaozi sink into the bottom of the pot after it cooled down?
Okay, can you answer that? Let's take a look at the mystery!
It turns out that with the heating of the stove, the water and jiaozi in the pot are heating up slowly. Objects will expand when heated, and jiaozi and water are no exception. But the degree of thermal expansion of different objects is different: some expand quickly, and some expand slowly. Jiaozi expands faster than water, so their volume can easily increase a lot. (Cooked jiaozi is generally full, much bigger than raw jiaozi. However, the weight of jiaozi did not increase. After the volume increased, the weight per unit volume, that is, the density decreased. According to Archimedes principle, we can know that the buoyancy of an object immersed in a liquid is equal to the weight of the same volume of liquid. After jiaozi is cooked, the stuffing and skin of dumplings are fully expanded. At this time, the density of jiaozi is less than that of water, and the weight of jiaozi with the same volume is less than that of water with the same volume. According to Archimedes principle, the buoyancy of jiaozi immersed in water is equal to the weight of the same volume of water. So the buoyancy of jiaozi is greater than its own weight, and jiaozi floats. Therefore, jiaozi can only float if it is cooked, that is, the dumpling stuffing and dumpling skin are fully expanded. Eat jiaozi float, of course, there will be no worries.
Why did jiaozi sink when it was a little cooler after it floated? A rapidly expanding object will contract rapidly. When water cools, jiaozi shrinks much faster than water. In this way, after jiaozi contracts, the weight per unit volume increases and the buoyancy of water decreases. The reduced buoyancy was no longer enough to make jiaozi, whose weight per unit volume increased, float, so jiaozi sank to the bottom of the pot again.
You see, there are so many reasons for the ups and downs in jiaozi! To explain these truths, we need to learn more about science and culture. Readers, let's study hard together!