Damping refers to the gradual reduction of the vibration amplitude caused by external effects and/or inherent reasons of the system in any vibration system, and Quantitative characterization of this feature. In electricity, it is almost the meaning of response time. In mechanical physics, the energy of the system is reduced-damping vibration is not caused by "resistance". In terms of mechanical vibration, one is caused by friction resistance, reduce the mechanical energy of the system and convert it to the internal energy. This damping is called the Friction Damping. The other is that the system causes the vibration of the surrounding particle, so that the system energy gradually emits to the surrounding area, the energy of a wave. This damping is called radiation damping. The friction takes a stable time! Time when the pointer multimeter remains stable! In mechanical systems, linear viscous damping is the most common damping model. The size of the damping force r is directly proportional to the speed of the moving particle. In the opposite direction, r =-C, and C is the viscous damping coefficient. The numerical value must be determined by the vibration test. Because the Mathematical Solution of Linear Systems is simple, in engineering, other types of damping are often converted into equivalent viscous damping according to their principle of equal energy loss in a cycle. The motion of an object changes with the size of the damping coefficient of the system. For example, in a vibration system with a degree of freedom, [973-01] is called the critical damping factor. Formula is the mass of the particle, and K is the stiffness of the spring. The actual ratio of viscous damping coefficient C to critical damping coefficient C is called damping ratio. <1 is called underdamping, and the object undergoes logarithm attenuation vibration.> 1 is called Over Damping, and the object returns to the equilibrium position slowly without vibration. Underdamping has little impact on the system's inherent frequency value, but the amplitude of the free vibration degrades rapidly. Damping can also significantly reduce the amplitude of forced vibration in the vicinity of the resonance zone, while damping far from the resonance zone has little impact on the amplitude. The new large damping material and squeeze oil film bearing have a significant damping effect. In some cases, viscous damping does not fully reflect the actual situation of energy dissipation in mechanical systems. Therefore, when studying mechanical vibration, models such as delayed damping, proportional damping, and nonlinear damping are also established. The behavior of a system behavior system is determined by the two parameters defined in the above summary: natural frequency ω N and damping ratio ε. In particular, the quadratic equation about gamma at the end of the above section determines the qualitative behavior of the system, whether it has a pair of mutually exclusive real numbers, a pair of duplicated real numbers, or a pair of bounded virtual numbers. The solution of critical damping is a one-to-multiple-root solution when the ε = 1. the damping form of the system is called critical damping. In real life, many room or bathroom doors in the building are equipped with a torsion spring that is automatically closed, and are equipped with a damping hinge, so that the damping of the door is close to the critical damping, in this way, when people close the door or the door is blown by the wind, it will not make too much sound. When the excess damping value is greater than 1, the solution is a pair of different real roots. In this case, the system's damping form is called the excess damping. When the damping hinge installed on the automatic door enables the door to have over-damping, it takes a longer time to automatically close the door.