Junior High School Physics: List of Knowledge of "Fever and Energy" in the first grade of junior high school, it is recommended to save!

Junior High School Physics: List of Knowledge of "Fever and Energy" in the first grade of junior high school, it is recommended to save!

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1. Molecular heat exercise:

1. Material is composed of molecules. If the molecule is regarded as a ball type, its diameter is 10-10m.

2. The molecules of all objects are constantly doing irregular exercise

① diffusion: When different substances are in contact with each other, they enter each other.

② Discounting phenomenon: There is a gap between A molecules. The B molecules are constantly doing irregular movements.

③ The purpose of placing nitric dioxide in the device in the textbook is: preventing the proliferation of nitric oxide is mistaken for gravity. Experimental phenomenon: Two bottles of gases are mixed together to become uniform. Conclusion: Gas molecules are constantly moving.

④ Solid, liquid, and gas can diffuse, and the diffusion speed is related to temperature.

⑤ The molecular movement is distinguished from the object movement: diffusion, evaporation, etc. are the result of molecular movement, while flying dust, liquid and gas convection are the result of object movement.

3. There is interactive gravitational and exclusion between molecules.

① When the distance between the molecule D = the balance between the between the molecule, the gravity = the exclusion force.

② D, the gravity

③D ＞ R, gravity> exclusion force, gravity played the main role. The solid is difficult to be pulled, the pen is written, and the glue sticky things are because of the gravity between molecules.

④ When D> 10R, the force between the molecules is very weak, but it can be ignored.

The reason why the mirror cannot be re -reunited is that the distance between the mirror block is much greater than the range of the force between the molecule, and the mirror cannot be combined by the force between the molecule.

Second, internal energy:

1. Internal energy: The sum of all molecules inside the object to do irregular movements and molecular potential energy is called the internal energy of the object.

2. In any case, there is an internal energy: Since the parts inside the object continue to move between the molecules, the internal energy is unconditional. Whether it is high -temperature iron or cold ice cubes.

3. Factors affecting the size of the object: ① Temperature: The higher the temperature, the higher the temperature when the quality, the same material, and the state. ② Quality: When the temperature, material, and state of the object are the same, the greater the quality of the object, the greater the internal energy of the object. ③ Materials: When the temperature, quality and state are the same, the material of the object is different, and the internal energy of the object may be different. ④ The state of existence: When the temperature and material quality of the object is the same, when the state of the object is different, the internal energy of the object may be different.

4. Internal energy is different from mechanical energy:

Mechanical energy is a macro, which is the energy that objects as an overall movement. Its size is related to mechanical movement

Internal energy is micro, which is the sum of the energy of all molecules inside the object. The size of the interior is related to the speed and slow movement of molecules and molecular effects. This random movement is the movement of molecules in objects, not the overall movement of objects.

5. Thermal movement: The irregular movements of a large number of molecules inside the object are called heat motion.

The higher the temperature, the faster. The higher the temperature, the greater the speed of the molecular irregular movement.

Third, the change of internal energy:

1. External performance that can be changed:

The temperature of objects increases (decreased) -Expressing (decrease) in objects.

The state of the object changes (melting, vaporization, sublimation) -The can change internal.

Conversely, it cannot be said that internal changes are inevitable to cause temperature changes. (Because there are many factors in the internal energy changes, it is determined)

2. Methods to change the internal energy: work and heat transfer.

A. Make work to change the internal energy of the object:

① The work can change the internal energy: the ability to make the object can increase. Objects can be reduced to the outside.

② The essence of changing the internal energy is the mutual conversion of internal energy and other forms of energy

③ If you only change the internal energy through the work, you can change the size of the energy in the amount of work. (W = △ E)

④ Explanation example: Figure 15.2-5 A see that cotton is burned. This is because the piston compressed air work, which increases the air in the air and increases the temperature to reaches the cotton burning point to burn cotton. Drilling wood: Make the woods rubbing each other, and the people do the wood to make it, increase its internal can increase, the temperature increases, and the burning point of the wood is burned. Figure 15.2-5 When I saw that when the plug jumped, there was a mist appearing in the container. This is because the air in the bottle pushed the plug to do the bottle plug. The inside could be reduced and the temperature was reduced, so that the water vapor liquefied into a small water droplet.

B. Thermal transmission can change the internal energy of the object.

① The phenomenon of heat transfer is the phenomenon that heat from high temperature to low -temperature objects or from the high temperature part of the same object to the low temperature part.

② The condition of the heat transfer is the temperature difference. The transmission method is: conduction, convection and radiation. The heat transfer is internal energy (heat), not temperature.

③ During the heat transmission process, the object absorbs heat, the temperature increases, and the internal energy increases; the inspiration temperature decreases, and the internal energy can be reduced.

④ During the heat transfer process, the amount of energy passed is called calories, and the unit of calories is scorched ears. The essence of heat transfer is the transfer of internal energy.

C. The difference between work and heat transfer changes: Since the effects that can be generated in the internal can be changed, it is equivalent to saying that work and heat transfer changes in the object. However, the essence of work and heat transfer changes in the essence of energy. The form of the former can change, and the form of the latter can remain unchanged. D, temperature, heat, internal energy difference:

△ Temperature: indicates the degree of hot and cold of objects.

Rise temperature - → Internal can increase

Not necessarily heat. Such as: drilling wood to get fire, friction and heat.

△ heat: It is a process.

The absorption of heat does not necessarily heat up. Such as: crystal melting,

Internal energy does not necessarily increase. Such as: absorbing calories all work, and internal energy may remain unchanged.

△ Internal energy: It is a status amount

Internal capacity is not necessarily heating. Such as: crystal melting, boiling water.

Not necessarily heat. Such as: drilling wood to get fire, friction and heat

☆ Point out the meaning of "heat" in the following physical nouns:

The "heat" in heat transfer refers to: "heat" in heat and heat refers to: temperature

The "heat" in thermal expansion refers to: "heat" in temperature friction of raw heat refers to: internal energy (thermal energy)

Fourth, calories:

1. Comparison of heat capacity: ⑴ Definition: The temperature of a certain material temperature of the unit quality increases (reduced) 1 ° C (released) during 1 ° C.

物 Physical significance: It means the physical quantity of an object's ability to absorb heat or holding heat.

(3) The heating capacity is a characteristic of the material. The size is related to the type and state of the object, which has nothing to do with quality, volume, temperature, density, heat absorption, shape, etc.

The heat capacity of 4 water is 4.2 × 103J (kg · ℃) indicate: the heat of 1kg of water increase (decrease) 1 ℃ absorbing (released) is 4.2 × 103J

、 Water often adjusts temperature, heating, cooling agent, and heat dissipation because the water is larger than the heat capacity

2. Calculating formula: ＝ suction = CM (T0), ｑ = CM (T0 -T)

3. Thermal equilibrium equation: regardless of heat loss ｑ = ｑ 放

Fifth, the use of internal energy, hot machine

(1) Internal acquisition -the combustion of fuel

Fuel combustion: Chemical energy can be transformed into internal energy.

(2) Hot value

1. Definition: The calories completely burned by 1kg of fuel are called the heat value of this fuel.

2. Unit: J/KG

3. Understanding of heat value:

① For the concept of heat value, we must pay attention to understanding the three keywords "1kg", "certain fuel", and "completely burning". 1kg is for the quality of fuel. If the quality of the fuel is not 1kg, then the calories that the fuel is completely burned is not a thermal value. Some kind of fuel: explain that thermal value is related to the type of fuel. Complete combustion: It means that it must be completely burned, otherwise the transformation of 1kg fuel chemistry to internal energy is not the value determined by the thermal value.

② The thermal value reflects a combustion characteristics of a certain substance, and at the same time reflects the ability of chemical can be transformed into an internal energy in different fuel combustion, that is, it is a characteristic of the fuel itself. The type of type is related to the shape, quality, and volume of fuel.

3. Formula: Q = mq (Q is the heat value).

In actual, the q suction = q is used to put CM (t-t0) = ηqm ′ combined problem.

4. The thermal value of alcohol is 3.0 × 107J/kg, which indicates that 1kg of alcohol is completely burned and released is 3.0 × 107J.

The thermal value of the gas is 3.9 × 107J/m3, which indicates that the calories completely burned by 1m3 gas are 3.9 × 107J.

5. Rockets are commonly used for liquid hydrogen for fuel because: the thermal value of liquid hydrogen is large, and small volume is easy to store and transport

6. The efficiency of the stove:

① Definition: The ratio of calories and fuels that the stove effectively uses is completely burned.

② Formula: q = q effective/ q total = cm (t-t0)/ qm ′

(3) Utilization of Nengneng

1. The use of internal energy:

⑴ Use the internal energy to heat; from the perspective of energy, this is the process of internal energy.

⑵ Use internal energy to do work; from a capacity point of view, this is the transformation of internal energy into mechanical energy.

2. Heat: Definition: The installation of the combustion of fuel.

Can transform: Internal energy is transformed into mechanical energy

Steaming machine -internal combustion engine -jet engine

3. Internal combustion engine: Move the fuel to the internal combustion of the machine, convert it into a machine that can work in the internal capacity and use internal capacity to work. It mainly includes gasoline and diesel engines.

4. The approximate working process of internal combustion engines: Each working cycle of internal combustion engines is divided into four stages: aspiration, compression stroke, work, and exhaust stroke. In these four stages, the inhalation of the breath, the compression stroke, and the exhaust stroke are done by the inertia of the flywheel, and the effort is the only way to do the external work in the internal combustion engine, which is transformed from internal energy to mechanical energy. In addition, the compression stroke transforms mechanical energy into internal energy.

5. The efficiency of the thermal machine: The ratio of the energy used to do the energy and the energy of the entire combustion is called the efficiency of the hot machine.

Formula: = = W is useful/ q total = w useful/ qm

The way to improve the efficiency of thermal machine: fully burn the fuel to reduce the lubrication and reduce friction between various heat loss.

6. Comparison of gasoline and diesel engines:

6. The law of energy conservation

1. There are various forms of energy in nature. Although we have not studied systematically, we have also understood in daily life. For example Chemical energy, etc. 2. Under certain conditions, various forms of energy can be transformed and transferred to each other (listing the examples of students familiar with, explaining the transformation and transfer of various forms of energy). During the heat transfer process, the internal energy of high -temperature objects can be transferred to low -temperature objects. Sports A steel balls hit the still steel ball, and the mechanical energy of A ball is transferred to B ball. The energy form has not changed in this transfer process.

3. The transformation of energy in nature is also common. Children's slippery ladders are transformed into internal energy due to friction; in the phenomenon of gas expansion and work, internal energy is transformed into mechanical energy; in hydropower, water mechanical energy can be converted into electrical energy; Energy, transform into electrical energy; in nuclear power plants, nuclear energy is transformed into electrical energy; when current is transmitted to the electric heater, the electrical energy is converted into internal energy;

4. Energy Conservation Law: Energy will neither eliminate nor creative students. It will only be converted from one form to other forms, or from one object to another The total amount remains unchanged.

The law of energy transformation and conservation is one of the most common and important laws in nature.

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