What conversion methods are used in junior high school physics?

Equivalent substitution method, control variable method.

equivalent substitution, etc.

Transformation method: For some invisible and intangible material or physical problems, we often have to put aside the things themselves, and understand things by observing and studying their explicit characteristics, phenomena or effects in nature, which is called transformation method in physics. It is a commonly used scientific method to help us understand abstract physical phenomena such as:

When we understand and study the theory that molecules are moving irregularly without stopping, because molecules are microscopic and cannot be directly seen with the naked eye, we can recognize and understand them through diffusion phenomena that can be directly observed or felt; The current cannot be seen or touched, and we can judge its existence by the effects of various currents; The magnetic field cannot be seen or touched, and we can judge its existence by the pointing or deflection of the small magnetic needle and the effect of some other magnetic fields; In the same way, when studying whether an object is electrified, we cannot directly see whether the object is electrified, but we can judge whether the object is charged by observing the opening and closing of the tin foil on the electroscope; When studying the presence of air and atmospheric pressure, we can prove the existence of air and atmospheric pressure by feeling the flow of air and various applications of atmospheric pressure in real life.

By the way, many instruments are manufactured using the conversion method. For example, a thermometer is made by converting the temperature that cannot be seen or touched into the rise and fall of the liquid column. A manometer is created by converting the invisible and untouchable liquid pressure into the height difference between the two liquid levels.

There are also analogy methods, transformation methods, and ideal experimental methods.

1. Measure the volume of irregular stones

The volume of the stone is converted into the volume of the water drained for measurement.

2. Experiment to measure the length of the curve.

The length of the curve is converted into the length of the thin cotton thread for measurement.

3. Measuring sliding friction experiments.

The friction force is converted into the measurement of the tensile force.

4. Measure the diameter of the coin.

The diameter of the coin is converted into the length of the scale for measurement.

5. Experiments in the presence of magnetic fields.

The existence of a magnetic field is proved by the effect of a magnetic field.

6. Experiments on the factors of electric heat, current and resistance.

The amount of electric heat is converted into the height of the liquid column and measured.

The measurement accuracy can be improved by using the conversion method to convert unmeasurable quantities into measurable quantities, and also to convert unmeasurable quantities into measurable quantities.

For example, the story of Cao Chong's elephant weighing in ancient China is to convert the mass of an elephant that cannot be directly weighed into the mass of a measurable stone, which contains the ideological method of conversion method; The use of Archimedes' principle to measure the volume of irregular objects is to convert the volume that is not easy to measure into buoyancy that is easy to measure, which improves the measurement accuracy.

In addition, the moment of inertia of the rigid body is measured by measuring the period of the three-line pendulum, and the moment of inertia of the rigid body is measured by the falling time or angular acceleration of the rotation by the falling body method.

Due to the many interrelated relationships and effects between different physical quantities, there are different conversion measurement methods, which is the most groundbreaking aspect of physical experiments. The transformation of measurement methods has made the physical experimental methods more closely related to the development of various disciplines, and has penetrated into various disciplines.

Conversion measurement methods can be broadly divided into parametric conversion method and energy conversion method.

1. The application of "transformation method" in acoustics: we know that the loudness of the sound emitted by the sound emitter is related to the amplitude of the object, but sometimes the amplitude of some objects such as tables, gongs and drums is not easy to observe directly with the naked eye, at this time, we can put a small mass paper ball on the table, gongs and other vibrating objects, so that the amplitude of the table that is difficult to see is converted into the amplitude of the paper ball that is easy to see, and the amplitude of the paper ball reflects the amplitude of the table. This allows you to know the loudness of the sound emitted when the table vibrates.

2. The application of "conversion method" in thermalism: we know that in order to compare the calorific value of two fuels, it is to compare the amount of heat released when two fuels of equal mass are completely combusted, and the amount of heat released cannot be directly measured with measuring tools, so we convert the amount of heat released when the fuel is completely burned into the amount of water of the same mass to heat up, and the temperature of the water can be directly measured with a thermometer. In this way, we can use a thermometer to measure how much the temperature of the water of the same mass changes, so as to compare the calorific value of different fuels.

3. The application of "transformation method" in mechanics: because the effect of pressure, that is, the size of the pressure, cannot be directly observed with the naked eye, we can transform the pressure generated by the object to the degree of hand pain, the size of the sponge deformation, the depth of the yellow sand sagging, etc., so that the pressure generated by the object can be directly reflected; And when we study the kinetic energy of the motion of the object, we can convert the kinetic energy of the object into the amount of work done by the object on the external object (such as the wooden block), and the more work done by the moving object on the wooden block, the greater the kinetic energy of the moving object

4. The application of "conversion method" in electricity: when we study the resistance of conductors, we connect different conductors to both ends of the same power supply, and use the ammeter to see the current in the circuit, so as to know the size of the resistance of different conductors, and the larger the current in the circuit, the smaller the conductor's resistance to the current (i.e., resistance); In addition, when we study Joule's law, because the heat generated by the current flowing through the conductor cannot be perceived by the hand, and there is also the risk of the hand being burned, the new curriculum reform textbook grasps the characteristic that the matchstick will be ignited only when it reaches a certain ignition point, and the amount of heat generated by the current flowing through the conductor is converted into who ignites the matchstick first, which means that the current flowing through the conductor produces more heat first. Of course, when studying Joule's law, it is also possible to convert the amount of heat generated by the current flowing through the conductor to the heating of water of the same mass, and observe the temperature change of the water with a thermometer to know how much heat is generated by the current flowing through the conductor.

1. Comparing the current can be converted to observing the brightness and darkness of the bulb.

2. Comparing the magnetic strength of the electromagnet can be converted into observing the number of pins attracted by the electromagnet.

3. Joule's law experiment, compare how much exothermic can be converted into observing the temperature of kerosene.

The so-called "conversion method" mainly refers to the transformation of invisible and inconspicuous phenomena into visible and easily visible phenomena under the premise of ensuring the same effect; There are many ways to turn unfamiliar, complex questions into familiar, simple ones.

Measuring instruments: stopwatch, ammeter, voltmeter, resistance meter, spring dynamometer, barometer, micro piezometer, thermometer, tray balance, energy meter, electric pen ......

There are many more examples: the Magdeburg hemispheric experiment proves the existence of atmospheric pressure; The appearance of fog can prove that the air contains water vapor; The formation of shadows can prove that light travels in a straight line; The phenomenon of a lunar eclipse proves that the moon is not a source of light; The Oersted experiment proves the existence of a magnetic field around an electric current; The compass compass north proves the existence of a geomagnetic field; The phenomenon of diffusion proves that molecules move randomly; The lead block experiment can prove that there is a gravitational force between molecules; The fact that a moving object can do work externally proves that it has energy; The magnetic strength of the electromagnet can be shown by the number of electromagnets attracting iron nails; It can be explained by the bounce of the ping pong ball caused by the tuning fork that everything is vibrating, and so on, and if it is not enough, you can ask again.

Examples of the use of transformation methods in physics:

1. When judging whether there is current in the circuit, you can determine whether the bulb in the circuit emits light.

2. When it is necessary to prove whether there is water vapor in the air, prove the existence of water vapor in the air by observing the appearance of fog.

3. Observing the process of shadow formation, we can know that light travels in a straight line.

4. Molecules cannot be seen or touched, and if you want to study molecules, you can study it through diffusion phenomena.

5. The movement of the magnetic field cannot be seen or touched, and when judging whether the magnetic field exists, use a small magnetic needle to see if it rotates to determine.

6. If you want to prove the existence of the geomagnetic field, the compass compass can prove the existence of the geomagnetic field.

Difference Between Middle School Physics and High School Physics:

1. The depth of knowledge is different.

The main purpose of learning physics knowledge in junior high school physics is to use physics knowledge to explain various phenomena in life, and to use physics knowledge to analyze the causes of various problems, so as to find out the methods and measures to solve related problems.

In high school physics, to deepen the understanding of important physics knowledge, some will move from qualitative discussion to quantitative calculation, such as the relationship between force and motion, the concept of kinetic energy, electromagnetic induction, nuclear energy, etc.

2. The scope of knowledge is different.

Middle school physics includes electricity, mechanics, levers, power, heat, etc.

In high school physics, it is necessary to expand the scope of physics knowledge and learn many new contents that have not been learned in junior high school, such as the synthesis and decomposition of forces, Newton's law of universal gravitation, the theorem of momentum, the law of conservation of momentum, and the nature of light.

There are several experiments using the conversion method in junior high school physics.

Measure the volume of irregular stones. Replace the volume of the stone with the volume of boiling water and measure it. Experiment to measure the length of the curve.

The length of the curve is converted into the length of the thin cotton thread and measured. Tests on the measurement of sliding to search for friction. The friction force is converted into the measurement of the tensile force.

Experiment to measure the diameter of a coin. The diameter of the coin is converted into the length of the scale for measurement. Experiments in the presence of magnetic fields.

The existence of a magnetic field is proved by the effect of a magnetic field. Experiments to study the factors of electric heat and electric current and resistance. The amount of electric heat is converted into the height of the liquid column and measured.

Experiments to study what factors are related to electrical work. The amount of electrical work is converted into the height of the weight rise and measured.

There are several experiments using the conversion method in junior high school physics.

Measure the volume of irregular stones. The imitation age of the stone body is converted into the volume of drained water for measurement. An experiment to measure the length of the curve of the branch coat.

The length of the curve is converted into the length of the thin cotton thread for measurement. Experiments in measuring sliding friction. The friction force is converted into the measurement of the tensile force.

Experiment to measure the diameter of a coin. The diameter of the coin is converted into the length of the scale for measurement. Experiments in the presence of magnetic fields.

The existence of a magnetic field is proved by the effect of a magnetic field. Research and research chamber to study the factors of electric heat, electric current, and resistance. The amount of electric heat is converted into the height of the liquid column and measured.

Experiments to study what factors are related to electrical work. The amount of electrical work is converted into the height of the weight rise and measured.

Conversion method: In physics, for some invisible and intangible phenomena or physical quantities that are not easy to measure directly, some very intuitive phenomena are usually used to understand or easily measurable physical quantities are measured by interconnection, and this method of studying the problem is called the conversion method.

So-called"Conversion method"Under the premise of ensuring the same effect, the invisible and inconspicuous phenomena are converted into visible and easily visible phenomena; Transform unfamiliar and complex questions into familiar, simple ones; A method of converting physical quantities that are difficult to measure or accurate into physical quantities that can be measured or accurate. This method has been applied in many places in junior high school physics in the study of conceptual laws and experiments.

Application of pulley bridge:

Measuring instruments: stopwatch, ammeter, voltmeter, resistance meter, spring dynamometer, barometer, micro piezometer, thermometer, energy meter, electric pen.

Physical experiments: the causes of sound, the characteristics of liquid pressure, the factors that affect how much electric heat is generated by conductors, and the effect of pressure.