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In physics, physical quantities are values that describe the fundamental properties or states of matter or phenomena, such as length, mass, time, etc. And in order to describe and calculate these physical quantities more precisely, we introduced composite units and symbols. This article will use the various physical quantities listed in the table as examples to explore their combined units, symbols, and corresponding numerical meanings, with the aim of helping readers better understand the nature of physical quantities and their interrelationships. I. Area: square meters (m2). Area refers to the size of the two-dimensional space occupied by an object, and it is usually measured in square meters (m2). The square meter is a unit of area that is the square of a length unit, where m represents meter, one of the fundamental units in the International System of Units. When we say that the area of an object is 2 square meters, it means that the object occupies a rectangular space with dimensions of 2 meters by 1 meter, or 1 meter by 2 meters (or any other combination of side lengths whose product is 2). II. Volume: cubic meters (m3). Volume refers to the amount of three-dimensional space occupied by an object, and it is usually measured in cubic meters (m3). Cubic meter is a unit of volume that indicates an object occupies a cubic space of 1 meter × 1 meter × 1 meter. When we say that the volume of an object is 3 cubic meters, it means that this object occupies the space of three such cubes. III. Speed: meters per second (m/s). Speed is a physical quantity that describes how fast an object is moving, and it is usually measured in meters per second (m/s). This unit indicates that the distance an object moves per second is 1 meter. Speed is a vector, having both magnitude and direction. When we say that an object’s speed is 2 meters per second, it means that the object moves a distance of 2 meters in one second in a certain direction. IV. Acceleration: meters per second squared (m/s2). Acceleration is a physical quantity that describes the rate of change of an object’s velocity, and it is typically measured in meters per second squared (m/s2). This unit indicates that the change in an object’s velocity per second is 1 meter per second. Acceleration is also a vector, with magnitude and direction. When we say that the acceleration of an object is 3 meters per second squared, it means that the object’s velocity increases by 3 meters per second each second. V. Wavenumber: The wavenumber per meter (m⁻1) is a physical quantity that describes the reciprocal of the wavelength in wave phenomena, and it is typically measured in units of per meter (m⁻1). This unit indicates the number of waves per meter of length. Wavenumber is a scalar, having only a magnitude and no direction. In wave phenomena, the greater the wavenumber, the more dense the waves are ； The smaller the wavenumber, the sparser the waves. VI. Density: kilograms per cubic meter (kg/m3). Density is a physical quantity that describes the mass of a substance per unit volume, and it is usually expressed in units of kilograms per cubic meter (kg/m3). This unit indicates that the mass contained in each cubic meter of volume is 1 kilogram. Density is an inherent property of a substance, related to its type and state. Different substances have different densities, and the density of the same substance can also vary in different states. VII. Current density: Ampere per square meter (A/m2). Current density is a physical quantity that describes the amount of current flowing through a conductor per unit area, and it is typically measured in units of amperes per square meter (A/m2). This unit indicates that the current flowing per square meter is 1 ampere. Current density is one of the important parameters describing a conductor’s electrical conductivity, and it is related to the material of the conductor, its cross-sectional area, and the magnitude of the current flowing through it. VIII. Magnetic field strength: Ampere per meter (A/m). Magnetic field strength is a physical quantity that describes the intensity and direction of a magnetic field, and it is typically measured in units of amperes per meter (A/m). This unit indicates the strength of the magnetic field per meter of length. Magnetic field strength is a vector, with both magnitude and direction. In a magnetic field, the greater the magnetic intensity, the stronger the magnetic field ； The lower the magnetic field strength, the weaker the magnetic field. IX. Concentration of a substance: moles per cubic meter (mol/m3). The concentration of a substance is a physical quantity that describes the amount of solute present in a solution, and it is typically expressed in units of moles per cubic meter (mol/m3). This unit indicates that the number of moles of solute per cubic meter of volume is 1 mole. The concentration of a substance is one of the important parameters that describe the composition of a solution; it is related to the type of solute, the volume of the solution, as well as the mass or amount of substance of the solute. X. Specific volume: cubic meters per kilogram (m3/kg). Specific volume is a physical quantity that describes the volume occupied by a unit mass of a substance, and it is typically measured in cubic meters per kilogram (m3/kg). This unit indicates that the volume per kilogram of mass is 1 cubic meter. Specific volume is one of the inherent properties of a substance, and it is related to the type and state of the substance. Different substances have different specific volumes ； The specific volume of the same substance can also vary in different states. XI. Luminous intensity: Luminous intensity in candela per square meter (cd/m2) is a physical quantity that describes a light source’s ability to emit light over a unit area, and it is typically measured in candela per square meter (cd/m2). This unit indicates that the luminous intensity of the light source per square meter is 1 candela. Luminous intensity is one of the important parameters describing the brightness of a light source, and it is related to the type of light source, its power, and its luminous efficiency.