1, reference system

For other objects selected in advance as a reference to describe the motion of the object, all physical quantities related to the motion, such as the position and speed of the object under study, are relative to the object, while the values of the related physical quantities of the object selected as a reference system are zero.

Any application of physical laws and description of physical phenomena must be marked with the corresponding frame of reference, otherwise it is meaningless. General relativity tells us that the laws of physics are equal to all reference systems.

2. Coordinate system

Coordinate system is a frame based on number axis and a mathematical abstraction of reference system. Common coordinate systems are rectangular coordinate system, spherical coordinate system and cylindrical coordinate system.