Lead: We can compare the physical concept to a "system" with abstract appearance and complex connotation. Physical quantity is only the expression of the corresponding physical concept with the same name, and the physical concept has many other qualitative properties besides the nature of quantity. The following is my paper on the difference between physical concepts and physical quantities. Let's have a look.

In the published literature, there are many articles about the teaching of physical concepts, but in these published literature, many authors do not distinguish physical concepts and physical quantities well, confusing the boundaries between them, especially the physical concepts and physical quantities with the same name, which are often expressed as "quantitative physical concepts, that is, physical quantities" or "physical quantities are quantitative physical concepts".

In fact, there are essential differences between physical concepts and physical quantities: physical concepts are the premise of physics teaching papers and the basis of physical quantities, and physical quantities are subordinate to the corresponding physical concepts of the same name. Without physical concept, there is no physical quantity; Physical quantities usually have corresponding physical concepts with the same name, but physical concepts do not necessarily have corresponding physical quantities with the same name. Even though they have the same name, there are many differences between them. Physical concepts have richer meanings than physical quantities. The following is explained from two aspects.

1, the difference between generalized physical concepts and physical quantities

1. 1 has different definitions.

Physical concept is a generalization and abstract reflection of the same characteristics and essential attributes of a physical phenomenon in the human brain, and it is a thinking form that abstracts and summarizes physical phenomena and physical processes. The concept of physics is no longer an individual physical phenomenon, nor a specific physical process or physical state, but an abstraction and generalization of physical objects, physical processes and physical states with essential attributes in the physical world, so it is called "concept".

Quantity is the concrete representation and measurement of things in numerical value. Physical quantity is a quantity that measures the properties of matter or describes the motion state of an object and its changing process in physics. For physical quantities with units, they must be described by numbers and units at the same time, otherwise they cannot produce any physical meaning.

Because of different definitions, their meanings are naturally different. Physical concepts and physical quantities describe physical phenomena, physical facts or physical processes from different angles.

1.2 was introduced for different purposes.

Generally speaking, as long as the essential attributes and characteristics of physical phenomena are abstracted and summarized, the physical concept is formed, which is a knowledge unit formed by the unique combination of characteristics. Physical concepts can be divided into two categories according to their essential attributes and the same characteristics: one is qualitative and prescriptive concepts, such as mechanical motion, simple harmonic motion, interference and polarization. The other is the concept with both qualitative and quantitative provisions, such as speed, acceleration, electric field strength, resistance, electromotive force and so on.

For the second concept, in addition to expressing its qualitative attributes, it is also necessary to clearly express its quantitative attributes. How to express it? This urges people to measure and express their abstract objects with concrete numerical values, so that physical quantities can be introduced, which have the same name as the corresponding physical concepts. It can be seen that the introduction of physical quantities should be based on the established physical concepts of the same name, and its purpose is only to quantify the quantitative attributes of the physical concepts of the same name, so physical quantities are subordinate to physical concepts. Physical quantities usually have corresponding physical concepts with the same name, but physical concepts do not necessarily have corresponding physical quantities with the same name, and the scope of physical concepts is wider than physical quantities.

Of course, because quantity itself contains the double meanings of number and degree, as the introduction of each physical quantity, it also gives quantitative expression and measurement to the abstract generalization object of the corresponding physical concept, which of course makes the corresponding physical concept more scientific, and physical quantity is a necessary supplement and quantification to the physical concept.

1.3 has different functions.

Physical concepts are the basis of physical laws and theories, because physical laws reveal the mutual relations and constraints between physical concepts. For example, if students don't know the concepts of force, mass and acceleration, they can't master and understand Newton's second law, let alone apply it correctly. It can be said that without a series of concepts as the basis, it is impossible to form a physical system. For another example, without a series of concepts such as circuit, current, voltage, resistance, magnetic induction intensity and electromagnetic induction, it is impossible to form an electromagnetic system; Without a series of concepts such as light source, light, real image and virtual image, it is impossible to form an optical system.

Therefore, physical concepts are the basic elements of physics, and the learning of physical concepts is at the core of the whole physical learning.

Physical quantities give meaning to the corresponding physical concept size. Under certain conditions, mathematical operations can be performed between physical quantities, which makes it possible to define new physical quantities. Because each physical quantity has a corresponding symbol, the physical expression is more concise and beautiful, and the quantitative expression of physical laws makes physics a quantitative discipline, which makes the conclusions of physics can be strictly tested at any time, which is conducive to human understanding of nature and grasping the laws. The combination of qualitative expression of physical concepts and laws with accurate mathematical quantitative expression constitutes one of the outstanding characteristics of physics.

1.4 classification is different.

Physical quantities can be divided into basic physical quantities and derived physical quantities, but physical concepts are only basic concepts in a broad sense, and there is no basic concept.

1960 1 1 International Metrology Conference 1960 In June, the international system of units was established, referred to as SI system for short. In the international system of units, seven physical quantities are generally selected as basic physical quantities (whose units correspond to basic units), and the rest are derived physical quantities, and the corresponding units are derived units. The derived physical quantity is defined by two or more other physical quantities and needs to be expressed by a certain physical formula (mathematical expression).

However, although physical concepts are only basic concepts in a broad sense, there is no expression of basic concepts, but there are levels (note: this paper does not explain other classification methods of concepts). Concepts may be the relationship between upper-level concepts and lower-level concepts, or parallel relationships, or inclusion relationships. Only by clarifying the hierarchical relationship between concepts can we better understand concepts, which can be done by drawing concept maps. For example, if energy is regarded as an upper concept, its potential energy, kinetic energy, internal energy and so on are its lower concepts, and potential energy includes more specific concepts such as gravitational potential energy, electric potential energy and molecular potential energy. After understanding the level of physical concepts, we can correctly distinguish the laws that are easily confused, such as conservation of energy and conservation of mechanical energy, and students will have no problems or fewer problems when applying these laws.

2. The difference between physical concepts and physical quantities with the same name.

Physical quantities and physical concepts sometimes have exactly the same names and correspond to each other. Physical quantities and corresponding physical concepts are consistent in expressing and reflecting objects and corresponding in appearance. However, they are essentially different in physical meaning and meaning, which determines that they have obvious anisotropy in definition methods and functions, which is also the most confusing place for teachers.

For example, force is a physical concept and a physical quantity with the same name. Force, as a physical quantity, is defined as the force required for an object with 1 kg to obtain an acceleration of 1 m/s2, that is,1n; Modern physics also defines force as the rate of change of momentum of an object; Force is a vector; Usually expressed as pulling force F=8 N, and the direction is east; Force is not a basic physical quantity and so on. As a physical concept, force is defined as the action of objects on objects; In addition to the properties of the above physical quantities, there are other characteristics: force has materiality and reciprocity; It has three elements: size, direction and action point; There are also specific forces such as gravity, elasticity, friction and electric field force; It has instantaneous effect, time accumulation effect and space accumulation effect, and the concept has richer connotation and extension.

For another example, work is an important concept in high school, and it has a corresponding physical quantity with the same name. As a physical quantity, its definition is W=Fscosθ, which can be understood as zero work, positive work and negative work; Work is related to the frame of reference; This formula is suitable for constant force, if it is variable force, it should be treated accordingly; Work is scalar; Its unit is joule, the sum of force and work is the combined work, and so on. But if we take work as a physical concept, it is not enough to understand the above aspects! For the concept of work, students can only understand why the product of force and displacement should be used to define work after learning the function relation or kinetic energy theorem. Only by learning the law of conservation of mechanical energy, the first law of thermodynamics and the law of conservation of energy can students truly understand the essence of the concept of work: work is a measure of energy transformation, and all processes of doing work are processes of energy transformation.

For another example, resistance is both a concept and a physical quantity. As a physical quantity, resistance is defined as R=UI, which provides an important method to measure resistance. As a concept, what role does resistance play in the circuit besides size? What determines the resistance? How did the nature of resistance come into being? ..... Many other concepts with the same name have similar characteristics.

It can be seen that the physical concept of the same name is more complicated than the corresponding physical quantity, involving a wider range, and contains other rich information besides the information of the corresponding physical quantity.

With the help of physical quantities, physical laws can be presented in the form of physical formulas (mathematical expressions). On the surface, these physical formulas only involve physical quantities, but in fact they are the interrelations and constraints of physical concepts. Only by understanding physical concepts can we master these physical formulas and laws. Therefore, remembering physical formulas is a necessary condition for learning physics well, but it is not enough. If we ignore the understanding of physical concepts and only pay attention to the study of physical quantities, we will fall into the wrong understanding that "physics is only memorizing formulas", and students will also have the situation that "formulas are memorized and they fail in the exam".

In short, through the above comparison, we can see that there are many differences between physical concepts and physical quantities, and they are different physical terms. Compared with physical quantities, it can be said that physical concepts are superior, more abstract and contain more information. Physical quantity is only the expression of the corresponding physical concept with the same name, and the physical concept has many other qualitative properties besides the nature of quantity.

We can compare the physical concept to a "system" with abstract appearance and complex connotation, which includes the purpose (or background), definition, physical meaning, relationship with other concepts and other properties. If the concept has quantitative attributes, there are corresponding physical quantities with the same name.

Knowing the difference between them, teachers will not simplify concept teaching to physical quantity teaching, let alone to formula teaching, which will naturally help students learn physical concepts, not only know why, but also better grasp physical concepts as a whole and in essence.

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